fix: correct token/cost double-counting in usage tracker

Remove the StepUsageEvent handler from subscribeSDKEvents. It was
calling UpdateUsage() for every individual tool-calling step as it
streamed, then updateUsageFromTurnResult() called UpdateUsage() again
with TotalUsage (fantasy's own aggregate of all steps). A turn with N
tool calls was counting every token N+1 times.

Fix updateUsageFromTurnResult to use a single, clean code path:
- UpdateUsage() called exactly once per turn using TotalUsage
- SetContextTokens() uses FinalUsage.InputTokens only (not +OutputTokens)
  since input tokens of the last call = actual context window fill;
  output tokens are the response length, not context occupancy
- Estimate fallback no longer early-returns before SetContextTokens

Verified with opencode/kimi-k2.5: cost accumulates linearly across
simple and multi-step tool-calling turns with no double-counting.
anthropic/claude-sonnet-4-6 correctly shows $0.00 for OAuth sessions.

.agents/skills/btca-cli/SKILL.md

@@ -1,64 +0,0 @@
----
-name: btca-cli
-description: Operate the btca CLI for local resources and source-first answers. Use when setting up btca in a project, connecting a provider, adding or managing resources, and asking questions via btca commands. Invoke this skill when the user says "use btca" or needs to do more detailed research on a specific library or framework.
----
-
-# btca CLI
-
-`btca` is a source-first research CLI. It hydrates resources (git, local, npm) into searchable context, then answers questions grounded in those sources. Use configured resources for ongoing work, or one-off anonymous resources directly in `btca ask`.
-
-Full CLI reference: https://docs.btca.dev/guides/cli-reference
-
-Add resources:
-
-```bash
-# Git resource
-btca add -n svelte-dev https://github.com/sveltejs/svelte.dev
-
-# Local directory
-btca add -n my-docs -t local /absolute/path/to/docs
-
-# npm package
-btca add npm:@types/node@22.10.1 -n node-types -t npm
-```
-
-Verify resources:
-
-```bash
-btca resources
-```
-
-Ask a question:
-
-```bash
-btca ask -r svelte-dev -q "How do I define remote functions?"
-```
-
-## Common Tasks
-
-- Ask with multiple resources:
-
-```bash
-btca ask -r react -r typescript -q "How do I type useState?"
-```
-
-- Ask with anonymous one-off resources (not saved to config):
-
-```bash
-# One-off git repo
-btca ask -r https://github.com/sveltejs/svelte -q "Where is the implementation of writable stores?"
-
-# One-off npm package
-btca ask -r npm:react@19.0.0 -q "How is useTransition exported?"
-```
-
-## Config Overview
-
-- Config lives in `btca.config.jsonc` (project) and `~/.config/btca/btca.config.jsonc` (global).
-- Project config overrides global and controls provider/model and resources.
-
-## Troubleshooting
-
-- "No resources configured": add resources with `btca add ...` and re-run `btca resources`.
-- "Provider not connected": run `btca connect` and follow the prompts.
-- "Unknown resource": use `btca resources` for configured names, or pass a valid HTTPS git URL / `npm:<package>` as an anonymous one-off in `btca ask`.

.agents/skills/btca-cli/agents/openai.yaml

@@ -1,3 +0,0 @@
-interface:
-  display_name: "BTCA CLI"
-  short_description: "Help with BTCA CLI setup and usage workflows"

.github/workflows/pages.yml

@@ -0,0 +1,32 @@
+name: Build and Deploy Docs to GitHub Pages
+
+on:
+  push:
+    branches: [master]
+  workflow_dispatch:
+
+jobs:
+  build-and-deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v4
+
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v1
+        with:
+          bun-version: latest
+
+      - name: Install Dependencies
+        working-directory: ./www
+        run: bun install
+
+      - name: Build
+        working-directory: ./www
+        run: bun run build
+
+      - name: Deploy to GitHub Pages
+        uses: JamesIves/github-pages-deploy-action@v4
+        with:
+          folder: www/out
+          branch: gh-pages

.gitignore

@@ -1,14 +1,16 @@
 .aider*
 .task/
 .env
-.kit/
+.kit/*
+!.kit/extensions/
 aidocs/
 *.log
 /kit
 .idea
-test/
 build/
 dist/
 contribute/output/
 CONTEXT.md
 output/
+.agents/
+skills-lock.json

.kit/extensions/go-edit-lint.go

@@ -0,0 +1,228 @@
+//go:build ignore
+
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"kit/ext"
+)
+
+const (
+	diagnosticsTimeout = 20 * time.Second
+	maxOutputBytes     = 12_000
+)
+
+type toolPathInput struct {
+	Path string `json:"path"`
+}
+
+type lintResult struct {
+	Output string
+	Err    error
+}
+
+func Init(api ext.API) {
+	api.OnSessionStart(func(_ ext.SessionStartEvent, ctx ext.Context) {
+		ctx.Print("go-edit-lint extension loaded - will run gopls and golangci-lint on Go file edits")
+	})
+
+	api.OnToolResult(func(e ext.ToolResultEvent, ctx ext.Context) *ext.ToolResultResult {
+		if e.IsError || !isEditOrWrite(e.ToolName) {
+			return nil
+		}
+
+		absPath, ok := resolveGoFilePath(e.Input, ctx.CWD)
+		if !ok {
+			return nil
+		}
+
+		report := runGoDiagnostics(ctx.CWD, absPath)
+		
+		// Check if there are issues and add explicit prompt for the LLM to react
+		goplsIssues, lintIssues := countIssues(report)
+		hasIssues := goplsIssues > 0 || lintIssues > 0
+		
+		var enhanced string
+		if hasIssues {
+			enhanced = e.Content + "\n\n" + report + "\n\n⚠️ DIAGNOSTICS FOUND: Please review the issues above and fix them before proceeding."
+		} else {
+			enhanced = e.Content + "\n\n" + report
+		}
+
+		// Show TUI message block for diagnostics visibility (only if there are issues)
+		if hasIssues {
+			var msgLines []string
+			msgLines = append(msgLines, fmt.Sprintf("File: %s", filepath.Base(absPath)))
+			if goplsIssues > 0 {
+				msgLines = append(msgLines, fmt.Sprintf("gopls: %d issue(s)", goplsIssues))
+			}
+			if lintIssues > 0 {
+				msgLines = append(msgLines, fmt.Sprintf("golangci-lint: %d issue(s)", lintIssues))
+			}
+			msgLines = append(msgLines, "", "⚠️ Please fix these issues before proceeding.")
+
+			borderColor := "#f9e2af" // yellow
+			if goplsIssues > 0 && lintIssues > 0 {
+				borderColor = "#f38ba8" // red
+			}
+
+			ctx.PrintBlock(ext.PrintBlockOpts{
+				Text:        strings.Join(msgLines, "\n"),
+				BorderColor: borderColor,
+				Subtitle:    "go-edit-lint",
+			})
+		}
+
+		return &ext.ToolResultResult{Content: &enhanced}
+	})
+}
+
+func isEditOrWrite(toolName string) bool {
+	return strings.EqualFold(toolName, "edit") || strings.EqualFold(toolName, "write")
+}
+
+func resolveGoFilePath(inputJSON, cwd string) (string, bool) {
+	var args toolPathInput
+	if err := json.Unmarshal([]byte(inputJSON), &args); err != nil || args.Path == "" {
+		return "", false
+	}
+
+	absPath := args.Path
+	if !filepath.IsAbs(absPath) {
+		absPath = filepath.Join(cwd, absPath)
+	}
+
+	if strings.ToLower(filepath.Ext(absPath)) != ".go" {
+		return "", false
+	}
+
+	return absPath, true
+}
+
+func runGoDiagnostics(cwd, absPath string) string {
+	gopls := runGopls(cwd, absPath)
+	lint := runGolangCILint(cwd, "./...")
+
+	return fmt.Sprintf(
+		"<go_diagnostics file=%q>\n[gopls]\n%s\n\n[golangci-lint]\n%s\n</go_diagnostics>",
+		filepath.Base(absPath),
+		formatToolResult(gopls, "No diagnostics."),
+		formatToolResult(lint, "No lint issues."),
+	)
+}
+
+func runGopls(cwd, absPath string) lintResult {
+	ctx, cancel := context.WithTimeout(context.Background(), diagnosticsTimeout)
+	defer cancel()
+
+	cmd := exec.CommandContext(ctx, "gopls", "check", absPath)
+	cmd.Dir = cwd
+	out, err := cmd.CombinedOutput()
+
+	if ctx.Err() == context.DeadlineExceeded {
+		return lintResult{Err: fmt.Errorf("timed out after %s", diagnosticsTimeout)}
+	}
+
+	if err != nil {
+		return lintResult{Output: truncate(string(out), maxOutputBytes), Err: fmt.Errorf("failed to run gopls check: %w", err)}
+	}
+
+	return lintResult{Output: truncate(string(out), maxOutputBytes)}
+}
+
+func runGolangCILint(cwd, target string) lintResult {
+	ctx, cancel := context.WithTimeout(context.Background(), diagnosticsTimeout)
+	defer cancel()
+
+	args := []string{
+		"run",
+		target,
+		"--show-stats=false",
+		"--output.text.path", "stdout",
+		"--output.text.colors=false",
+		"--output.text.print-issued-lines=false",
+	}
+	cmd := exec.CommandContext(ctx, "golangci-lint", args...)
+	cmd.Dir = cwd
+	out, err := cmd.CombinedOutput()
+
+	if ctx.Err() == context.DeadlineExceeded {
+		return lintResult{Err: fmt.Errorf("timed out after %s", diagnosticsTimeout)}
+	}
+
+	trimmed := truncate(string(out), maxOutputBytes)
+	if err == nil {
+		return lintResult{Output: trimmed}
+	}
+
+	exitErr, ok := err.(*exec.ExitError)
+	if ok && exitErr.ExitCode() == 1 {
+		return lintResult{Output: trimmed}
+	}
+
+	return lintResult{Output: trimmed, Err: fmt.Errorf("failed to run golangci-lint: %w", err)}
+}
+
+func formatToolResult(res lintResult, emptyFallback string) string {
+	var lines []string
+	if res.Err != nil {
+		lines = append(lines, "ERROR: "+res.Err.Error())
+	}
+	out := strings.TrimSpace(res.Output)
+	if out == "" {
+		if res.Err == nil {
+			lines = append(lines, emptyFallback)
+		}
+	} else {
+		lines = append(lines, out)
+	}
+	if len(lines) == 0 {
+		return emptyFallback
+	}
+	return strings.Join(lines, "\n")
+}
+
+func truncate(s string, max int) string {
+	if len(s) <= max {
+		return s
+	}
+	return s[:max] + "\n... output truncated ..."
+}
+
+func countIssues(report string) (goplsCount, lintCount int) {
+	// Extract gopls section
+	goplsStart := strings.Index(report, "[gopls]")
+	lintStart := strings.Index(report, "[golangci-lint]")
+	endTag := strings.Index(report, "</go_diagnostics>")
+
+	if goplsStart != -1 && lintStart != -1 {
+		goplsSection := report[goplsStart:lintStart]
+		// Count non-empty lines excluding the header and "No diagnostics." message
+		for _, line := range strings.Split(goplsSection, "\n") {
+			line = strings.TrimSpace(line)
+			if line != "" && line != "[gopls]" && line != "No diagnostics." {
+				goplsCount++
+			}
+		}
+	}
+
+	if lintStart != -1 && endTag != -1 {
+		lintSection := report[lintStart:endTag]
+		// Count non-empty lines excluding the header and "No lint issues." message
+		for _, line := range strings.Split(lintSection, "\n") {
+			line = strings.TrimSpace(line)
+			if line != "" && line != "[golangci-lint]" && line != "No lint issues." {
+				lintCount++
+			}
+		}
+	}
+
+	return goplsCount, lintCount
+}

.kit/extensions/subagent-monitor.go

@@ -0,0 +1,304 @@
+//go:build ignore
+
+// subagent-monitor — live horizontal widget strip for spawned subagents
+//
+// Subscribes to subagents spawned by the main Kit agent and displays a
+// single widget just above the input box. Each subagent occupies one column
+// in a side-by-side horizontal layout. Columns show scrolling real-time
+// output as the subagent works. When a subagent finishes its column is
+// removed automatically.
+//
+// Yaegi-safe design notes:
+// - No sync.Mutex (Yaegi has reflection issues with sync primitives)
+// - No channels in maps (Yaegi panics on range over map[string]chan)
+// - All ctx.* calls guarded with nil checks
+// - Simple data structures only
+package main
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"kit/ext"
+)
+
+// ---------------------------------------------------------------------------
+// Per-subagent state
+// ---------------------------------------------------------------------------
+
+type submonEntry struct {
+	id      int
+	callID  string
+	task    string
+	lines   []string
+	started time.Time
+	elapsed time.Duration
+}
+
+const (
+	submonColWidth = 34 // visible character width per column
+	submonMaxLines = 5  // scrolling output lines per column
+	submonColGap   = 2  // spaces between columns
+)
+
+// ---------------------------------------------------------------------------
+// Package-level state - all simple types
+// ---------------------------------------------------------------------------
+
+var (
+	submonCtx     ext.Context
+	submonHasCtx  bool
+	submonEntries []*submonEntry
+	submonNextID  int
+)
+
+func submonInit() {
+	submonEntries = nil
+	submonNextID = 1
+}
+
+// ---------------------------------------------------------------------------
+// String helpers
+// ---------------------------------------------------------------------------
+
+func submonPad(s string, w int) string {
+	r := []rune(s)
+	if len(r) >= w {
+		return string(r[:w])
+	}
+	return s + strings.Repeat(" ", w-len(r))
+}
+
+func submonTrunc(s string, w int) string {
+	r := []rune(s)
+	if len(r) <= w {
+		return s
+	}
+	if w <= 1 {
+		return "…"
+	}
+	return string(r[:w-1]) + "…"
+}
+
+// ---------------------------------------------------------------------------
+// Widget rendering
+// ---------------------------------------------------------------------------
+
+func submonRenderColumn(e *submonEntry) []string {
+	var rows []string
+
+	// Calculate elapsed time on-demand to avoid race conditions with ticker
+	elapsed := e.elapsed
+	if elapsed == 0 && !e.started.IsZero() {
+		elapsed = time.Since(e.started)
+	}
+	secs := int(elapsed.Seconds())
+	timeStr := fmt.Sprintf("%ds", secs)
+	taskMax := submonColWidth - len(timeStr) - 3
+	taskPart := submonTrunc(e.task, taskMax)
+	header := fmt.Sprintf("#%d %s  %s", e.id, taskPart, timeStr)
+	rows = append(rows, submonPad(header, submonColWidth))
+
+	display := e.lines
+	if len(display) > submonMaxLines {
+		display = display[len(display)-submonMaxLines:]
+	}
+	for _, l := range display {
+		rows = append(rows, submonPad("  "+submonTrunc(l, submonColWidth-2), submonColWidth))
+	}
+	for len(rows) < submonMaxLines+1 {
+		if len(rows) == 1 && len(e.lines) == 0 {
+			rows = append(rows, submonPad("  waiting…", submonColWidth))
+		} else {
+			rows = append(rows, strings.Repeat(" ", submonColWidth))
+		}
+	}
+	return rows
+}
+
+func submonBuildWidget() string {
+	if len(submonEntries) == 0 {
+		return ""
+	}
+
+	numCols := len(submonEntries)
+	numRows := submonMaxLines + 1
+	cols := make([][]string, numCols)
+	for i, e := range submonEntries {
+		rows := submonRenderColumn(e)
+		col := make([]string, numRows)
+		for j := 0; j < numRows; j++ {
+			if j < len(rows) {
+				col[j] = rows[j]
+			} else {
+				col[j] = strings.Repeat(" ", submonColWidth)
+			}
+		}
+		cols[i] = col
+	}
+
+	gap := strings.Repeat(" ", submonColGap)
+	var sb strings.Builder
+	for row := 0; row < numRows; row++ {
+		for ci := range cols {
+			if ci > 0 {
+				sb.WriteString(gap)
+			}
+			sb.WriteString(cols[ci][row])
+		}
+		if row < numRows-1 {
+			sb.WriteString("\n")
+		}
+	}
+	return sb.String()
+}
+
+func submonPushWidget() {
+	if !submonHasCtx {
+		return
+	}
+	if submonCtx.SetWidget == nil {
+		return
+	}
+
+	text := submonBuildWidget()
+	if len(submonEntries) == 0 {
+		if submonCtx.RemoveWidget != nil {
+			submonCtx.RemoveWidget("submon")
+		}
+		return
+	}
+	submonCtx.SetWidget(ext.WidgetConfig{
+		ID:        "submon",
+		Placement: ext.WidgetAbove,
+		Content:   ext.WidgetContent{Text: text},
+		Style:     ext.WidgetStyle{BorderColor: "#89b4fa"},
+		Priority:  0,
+	})
+}
+
+func submonAppendLine(e *submonEntry, line string) {
+	line = strings.TrimRight(line, "\r\n")
+	if strings.TrimSpace(line) == "" {
+		return
+	}
+	e.lines = append(e.lines, line)
+}
+
+// ---------------------------------------------------------------------------
+// Init
+// ---------------------------------------------------------------------------
+
+func Init(api ext.API) {
+	submonInit()
+
+	api.OnSessionStart(func(_ ext.SessionStartEvent, ctx ext.Context) {
+		submonCtx = ctx
+		submonHasCtx = true
+		submonInit()
+		if ctx.RemoveWidget != nil {
+			ctx.RemoveWidget("submon")
+		}
+	})
+
+	api.OnAgentEnd(func(_ ext.AgentEndEvent, ctx ext.Context) {
+		submonCtx = ctx
+		submonHasCtx = true
+	})
+
+	// ── SubagentStart ────────────────────────────────────────────────────────
+	api.OnSubagentStart(func(e ext.SubagentStartEvent, ctx ext.Context) {
+		submonCtx = ctx
+		submonHasCtx = true
+
+		id := submonNextID
+		submonNextID++
+		entry := &submonEntry{
+			id:      id,
+			callID:  e.ToolCallID,
+			task:    e.Task,
+			started: time.Now(),
+		}
+		submonEntries = append(submonEntries, entry)
+
+		submonPushWidget()
+	})
+
+	// ── SubagentChunk ────────────────────────────────────────────────────────
+	api.OnSubagentChunk(func(e ext.SubagentChunkEvent, ctx ext.Context) {
+		submonCtx = ctx
+		submonHasCtx = true
+
+		var entry *submonEntry
+		for _, en := range submonEntries {
+			if en.callID == e.ToolCallID {
+				entry = en
+				break
+			}
+		}
+		if entry == nil {
+			return
+		}
+
+		switch e.ChunkType {
+		case "text":
+			for _, line := range strings.Split(e.Content, "\n") {
+				submonAppendLine(entry, line)
+			}
+		case "tool_call":
+			submonAppendLine(entry, "→ "+e.ToolName)
+		case "tool_execution_start":
+			submonAppendLine(entry, "⚙ "+e.ToolName)
+		case "tool_result":
+			if e.IsError {
+				submonAppendLine(entry, "✗ "+e.ToolName)
+			} else {
+				submonAppendLine(entry, "✓ "+e.ToolName)
+			}
+		}
+
+		submonPushWidget()
+	})
+
+	// ── SubagentEnd ──────────────────────────────────────────────────────────
+	api.OnSubagentEnd(func(e ext.SubagentEndEvent, ctx ext.Context) {
+		submonCtx = ctx
+		submonHasCtx = true
+
+		var entry *submonEntry
+		for _, en := range submonEntries {
+			if en.callID == e.ToolCallID {
+				entry = en
+				break
+			}
+		}
+		if entry != nil {
+			entry.elapsed = time.Since(entry.started)
+			if e.ErrorMsg != "" {
+				submonAppendLine(entry, "✗ "+submonTrunc(e.ErrorMsg, submonColWidth-2))
+			}
+		}
+
+		submonPushWidget()
+
+		// Remove the entry immediately (no goroutine to avoid races)
+		newEntries := submonEntries[:0]
+		for _, en := range submonEntries {
+			if en.callID != e.ToolCallID {
+				newEntries = append(newEntries, en)
+			}
+		}
+		submonEntries = newEntries
+		submonPushWidget()
+	})
+
+	// ── SessionShutdown ──────────────────────────────────────────────────────
+	api.OnSessionShutdown(func(_ ext.SessionShutdownEvent, ctx ext.Context) {
+		submonInit()
+		// Guard ctx access - may be nil during shutdown
+		if ctx.RemoveWidget != nil {
+			ctx.RemoveWidget("submon")
+		}
+	})
+}

AGENTS.md

@@ -83,9 +83,9 @@ tmux kill-session -t kittest              # cleanup
 ### Non-Interactive Kit (Subprocess Spawning)
 Extensions can spawn Kit as a subprocess for sub-agent patterns:
 ```bash
-kit --prompt "question" --quiet --no-session --no-extensions --system-prompt /path/to/prompt.txt --model provider/model
+kit --quiet --no-session --no-extensions --system-prompt /path/to/prompt.txt --model provider/model "question"
 ```
-Key flags: `--quiet` (stdout only, no TUI), `--no-session` (ephemeral), `--no-extensions` (prevent recursive loading), `--system-prompt` (string or file path).
+Positional args are the prompt. `@file` args attach file content. Key flags: `--quiet` (stdout only, no TUI), `--no-session` (ephemeral), `--no-extensions` (prevent recursive loading), `--system-prompt` (string or file path).
 
 ## External Repo Research
 - **ALWAYS use `btca`** to search external repos (e.g. iteratr, other reference codebases)

README.md

@@ -13,4 +13,769 @@
 
 # KIT (Knowledge Inference Tool)
 
-TBD
+A powerful, extensible AI coding agent CLI with multi-provider support, built-in tools, and a rich extension system.
+
+## Features
+
+- **Multi-Provider LLM Support**: Anthropic, OpenAI, Google Gemini, Ollama, Azure OpenAI, AWS Bedrock, OpenRouter, and more
+- **Built-in Core Tools**: bash, read, write, edit, grep, find, ls, spawn_subagent - no MCP overhead
+- **MCP Integration**: Connect external MCP servers for expanded capabilities
+- **Extension System**: Write custom tools, commands, widgets, and UI modifications in Go
+- **Theming**: 22 built-in color themes (KITT, Catppuccin, Dracula, Nord, etc.) with runtime switching, persistence, and custom theme files
+- **Model Persistence**: Model and thinking level selections are automatically saved and restored across sessions
+- **Prompt Templates**: Create reusable prompt templates with shell-style argument substitution
+- **Interactive TUI**: Rich terminal interface powered by Bubble Tea with streaming, syntax highlighting, and custom rendering
+- **Session Management**: Tree-based conversation history with branching support
+- **Non-Interactive Mode**: Script-friendly positional args with JSON output
+- **ACP Server**: Run Kit as an [Agent Client Protocol](https://agentclientprotocol.com) agent over stdio
+- **Go SDK**: Embed Kit in your own applications
+
+## Installation
+
+### Using npm / bun / pnpm
+
+```bash
+npm install -g @mark3labs/kit
+# or
+bun install -g @mark3labs/kit
+# or
+pnpm install -g @mark3labs/kit
+```
+
+### Using Go
+
+```bash
+go install github.com/mark3labs/kit/cmd/kit@latest
+```
+
+### Building from source
+
+```bash
+git clone https://github.com/mark3labs/kit.git
+cd kit
+go build -o kit ./cmd/kit
+```
+
+## Quick Start
+
+### Basic Usage
+
+```bash
+# Start interactive session
+kit
+
+# Run a one-off prompt
+kit "List files in src/"
+
+# Attach files as context
+kit @main.go @test.go "Review these files"
+
+# Continue the most recent session
+kit --continue
+
+# Model and thinking level selections are automatically persisted
+# across sessions and restored on next launch
+
+# Use specific model
+kit --model anthropic/claude-sonnet-latest
+```
+
+### Non-Interactive Mode
+
+```bash
+# Get JSON output for scripting
+kit "Explain main.go" --json
+
+# Quiet mode (final response only)
+kit "Run tests" --quiet
+
+# Ephemeral mode (no session file)
+kit "Quick question" --no-session
+```
+
+### ACP Server Mode
+
+Kit can run as an [ACP (Agent Client Protocol)](https://agentclientprotocol.com) agent server, enabling ACP-compatible clients (such as [OpenCode](https://github.com/sst/opencode)) to drive Kit as a remote coding agent over stdio.
+
+```bash
+# Start Kit as an ACP server (communicates via JSON-RPC 2.0 on stdin/stdout)
+kit acp
+
+# With debug logging to stderr
+kit acp --debug
+```
+
+The ACP server exposes Kit's full capabilities — LLM execution, tool calls (bash, read, write, edit, grep, etc.), and session persistence — over the standard ACP protocol. Sessions are persisted to Kit's normal JSONL session files, so they can be resumed later.
+
+## Configuration
+
+Kit looks for configuration in the following locations (in order of priority):
+
+1. CLI flags
+2. Environment variables (with `KIT_` prefix)
+3. `./.kit.yml` / `./.kit.yaml` / `./.kit.json` (project-local)
+4. `~/.kit.yml` / `~/.kit.yaml` / `~/.kit.json` (global)
+
+### Basic Configuration
+
+Create `~/.kit.yml`:
+
+```yaml
+model: anthropic/claude-sonnet-latest
+max-tokens: 4096
+temperature: 0.7
+stream: true
+```
+
+### Environment Variables
+
+```bash
+export ANTHROPIC_API_KEY="sk-..."
+export OPENAI_API_KEY="sk-..."
+export KIT_MODEL="openai/gpt-4o"
+```
+
+### MCP Server Configuration
+
+Add external MCP servers to `.kit.yml`:
+
+```yaml
+mcpServers:
+  filesystem:
+    type: local
+    command: ["npx", "-y", "@modelcontextprotocol/server-filesystem", "/path/to/allowed"]
+    environment:
+      LOG_LEVEL: "info"
+    allowedTools: ["read_file", "write_file"]
+  
+  search:
+    type: remote
+    url: "https://mcp.example.com/search"
+```
+
+## CLI Reference
+
+### Global Flags
+
+```bash
+# Model and provider
+--model, -m              Model to use (provider/model format)
+--provider-api-key       API key for the provider
+--provider-url           Base URL for provider API
+--tls-skip-verify        Skip TLS certificate verification
+
+# Session management
+--session, -s            Open specific JSONL session file
+--continue, -c           Resume most recent session for current directory
+--resume, -r             Interactive session picker
+--no-session             Ephemeral mode, no persistence
+
+# Behavior (non-interactive: pass prompt as positional arg)
+--quiet                  Suppress all output (non-interactive only)
+--json                   Output response as JSON (non-interactive only)
+--no-exit                Enter interactive mode after prompt completes
+--max-steps              Maximum agent steps (0 for unlimited)
+--stream                 Enable streaming output (default: true)
+--compact                Enable compact output mode
+--auto-compact           Auto-compact conversation near context limit
+
+# Extensions
+--extension, -e          Load additional extension file(s) (repeatable)
+--no-extensions          Disable all extensions
+--prompt-template        Load a specific prompt template by name
+--no-prompt-templates    Disable prompt template loading
+
+# Generation parameters
+--max-tokens             Maximum tokens in response (default: 4096)
+--temperature            Randomness 0.0-1.0 (default: 0.7)
+--top-p                  Nucleus sampling 0.0-1.0 (default: 0.95)
+--top-k                  Limit top K tokens (default: 40)
+--stop-sequences         Custom stop sequences (comma-separated)
+--thinking-level         Extended thinking level: off, minimal, low, medium, high (default: off)
+
+# System
+--config                 Config file path (default: ~/.kit.yml)
+--system-prompt          System prompt text or file path
+--debug                  Enable debug logging
+```
+
+### Commands
+
+```bash
+# Authentication (for OAuth-enabled providers)
+kit auth login [provider]    # Start OAuth flow (e.g., anthropic)
+kit auth logout [provider]   # Remove credentials for provider
+kit auth status              # Check authentication status
+
+# Model database
+kit models [provider]        # List available models (optionally filter by provider)
+kit models --all             # Show all providers (not just Fantasy-compatible)
+kit update-models [source]   # Update model database (from models.dev, URL, file, or 'embedded')
+
+# Extension management
+kit extensions list          # List discovered extensions
+kit extensions validate      # Validate extension files
+kit extensions init          # Generate example extension template
+kit install <git-url>        # Install extensions from git repositories
+kit install -l <git-url>     # Install to project-local .kit/git/ directory
+kit install -u <git-url>     # Update an already-installed package
+kit install --uninstall <pkg> # Remove an installed package
+
+# Skills
+kit skill                    # Install the Kit extensions skill via skills.sh
+
+# ACP server
+kit acp                      # Start as ACP agent (stdio JSON-RPC)
+kit acp --debug              # With debug logging to stderr
+```
+
+## Themes
+
+Kit ships with 22 built-in color themes that control all UI elements. Switch at runtime:
+
+```
+/theme dracula
+/theme catppuccin
+/theme tokyonight
+```
+
+Theme selections are automatically saved and restored on next launch (stored in `~/.config/kit/preferences.yml`). This persistence also applies to **model** and **thinking level** selections — all are saved together and restored on startup.
+
+### Custom themes
+
+Drop a `.yml` file in `~/.config/kit/themes/` (user) or `.kit/themes/` (project):
+
+```yaml
+# ~/.config/kit/themes/my-theme.yml
+primary:
+  light: "#8839ef"
+  dark: "#cba6f7"
+success:
+  light: "#40a02b"
+  dark: "#a6e3a1"
+```
+
+Built-in themes: `kitt`, `catppuccin`, `dracula`, `tokyonight`, `nord`, `gruvbox`, `monokai`, `solarized`, `github`, `one-dark`, `rose-pine`, `ayu`, `material`, `everforest`, `kanagawa`, `amoled`, `synthwave`, `vesper`, `flexoki`, `matrix`, `vercel`, `zenburn`
+
+## Extension System
+
+Extensions are Go source files that run via Yaegi interpreter. They can add custom tools, slash commands, widgets, keyboard shortcuts, themes, and intercept lifecycle events.
+
+### Minimal Extension
+
+```go
+//go:build ignore
+
+package main
+
+import "kit/ext"
+
+func Init(api ext.API) {
+    api.OnSessionStart(func(_ ext.SessionStartEvent, ctx ext.Context) {
+        ctx.SetFooter(ext.HeaderFooterConfig{
+            Content: ext.WidgetContent{Text: "Custom Footer"},
+        })
+    })
+}
+```
+
+**Usage:**
+
+```bash
+kit -e examples/extensions/minimal.go
+```
+
+### Extension Capabilities
+
+**Lifecycle Events**: OnSessionStart, OnSessionShutdown, OnBeforeAgentStart, OnAgentStart, OnAgentEnd, OnToolCall, OnToolExecutionStart, OnToolOutput, OnToolExecutionEnd, OnToolResult, OnInput, OnMessageStart, OnMessageUpdate, OnMessageEnd, OnModelChange, OnContextPrepare, OnBeforeFork, OnBeforeSessionSwitch, OnBeforeCompact, OnCustomEvent, OnSubagentStart, OnSubagentChunk, OnSubagentEnd
+
+**Custom Components**:
+- **Tools**: Add new tools the LLM can invoke
+- **Commands**: Register slash commands (e.g., `/mycommand`)
+- **Options**: Register configurable extension options
+- **Widgets**: Persistent status displays above/below input
+- **Headers/Footers**: Persistent content above/below the conversation
+- **Status Bar**: Custom status bar entries
+- **Shortcuts**: Global keyboard shortcuts
+- **Overlays**: Modal dialogs with markdown content
+- **Tool Renderers**: Customize how tool calls display
+- **Message Renderers**: Custom rendering for assistant messages
+- **Editor Interceptors**: Handle key events and wrap rendering
+- **Interactive Prompts**: Select, confirm, input, and multi-select dialogs
+- **Subagents**: Spawn in-process child Kit instances
+- **LLM Completion**: Direct model calls via `Complete()`
+- **Themes**: Register and switch color themes via `RegisterTheme`, `SetTheme`, `ListThemes`
+- **Custom Events**: Inter-extension communication via `EmitCustomEvent`
+
+### Extension Examples
+
+See the `examples/extensions/` directory:
+
+- `minimal.go` - Clean UI with custom footer
+- `auto-commit.go` - Auto-commit on shutdown
+- `bookmark.go` - Bookmark conversations
+- `branded-output.go` - Branded output rendering
+- `compact-notify.go` - Notification on compaction
+- `confirm-destructive.go` - Confirm destructive operations
+- `context-inject.go` - Inject context into conversations
+- `custom-editor-demo.go` - Vim-like modal editor
+- `dev-reload.go` - Development live-reload
+- `header-footer-demo.go` - Custom headers and footers
+- `inline-bash.go` - Inline bash execution
+- `interactive-shell.go` - Interactive shell integration
+- `kit-kit.go` - Kit-in-Kit (sub-agent spawning)
+- `lsp-diagnostics.go` - LSP diagnostic integration
+- `notify.go` - Desktop notifications
+- `overlay-demo.go` - Modal dialogs
+- `permission-gate.go` - Permission gating for tools
+- `pirate.go` - Pirate-themed personality
+- `plan-mode.go` - Read-only planning mode
+- `project-rules.go` - Project-specific rules
+- `prompt-demo.go` - Interactive prompts (select/confirm/input)
+- `protected-paths.go` - Path protection for sensitive files
+- `subagent-widget.go` - Multi-agent orchestration with status widget
+- `subagent-test.go` - Subagent testing utilities
+- `summarize.go` - Conversation summarization
+- `tool-logger.go` - Log all tool calls
+- `neon-theme.go` - Custom theme registration and switching
+- `tool-renderer-demo.go` - Custom tool call rendering
+- `widget-status.go` - Persistent status widgets
+
+Also see `.kit/extensions/go-edit-lint.go` (in this repo) for a project-local extension example that runs gopls and golangci-lint on Go file edits.
+
+### Loading Extensions
+
+**Auto-discovery** (loads automatically):
+- `~/.config/kit/extensions/*.go` (global single files)
+- `~/.config/kit/extensions/*/main.go` (global subdirectory extensions)
+- `.kit/extensions/*.go` (project-local single files)
+- `.kit/extensions/*/main.go` (project-local subdirectory extensions)
+- `~/.local/share/kit/git/` (global git-installed packages)
+- `.kit/git/` (project-local git-installed packages)
+
+**Explicit loading**:
+```bash
+kit -e path/to/extension.go
+kit -e ext1.go -e ext2.go  # Multiple extensions
+```
+
+**Disable auto-load**:
+```bash
+kit --no-extensions
+```
+
+### Testing Extensions
+
+Kit provides a testing package to help you write unit tests for your extensions:
+
+```go
+package main
+
+import (
+    "testing"
+    "github.com/mark3labs/kit/pkg/extensions/test"
+    "github.com/mark3labs/kit/internal/extensions"
+)
+
+func TestMyExtension(t *testing.T) {
+    harness := test.New(t)
+    harness.LoadFile("my-ext.go")
+    
+    // Emit events and verify behavior
+    _, err := harness.Emit(extensions.SessionStartEvent{SessionID: "test"})
+    if err != nil {
+        t.Fatalf("unexpected error: %v", err)
+    }
+    
+    // Verify the extension printed something
+    test.AssertPrinted(t, harness, "session started")
+}
+```
+
+**Available assertions:**
+- `AssertBlocked()`, `AssertNotBlocked()` — Verify tool blocking
+- `AssertWidgetSet()`, `AssertWidgetText()` — Verify widget content
+- `AssertPrinted()`, `AssertPrintedContains()` — Verify output
+- `AssertToolRegistered()`, `AssertCommandRegistered()` — Verify registration
+
+See `examples/extensions/tool-logger_test.go` for a complete example with 14 test cases covering tool calls, input handling, and session lifecycle.
+
+### Prompt Templates
+
+Create reusable prompt templates with shell-style argument substitution. Templates are loaded from `~/.kit/prompts/*.md` and `.kit/prompts/*.md`.
+
+**Example template** (`~/.kit/prompts/review.md`):
+```markdown
+---
+description: Review code for issues
+---
+Review the following code for bugs and security issues.
+Focus on $1 specifically.
+```
+
+**Usage:**
+```
+/review error handling
+```
+
+**Argument placeholders:**
+- `$1`, `$2`, etc. — Individual arguments
+- `$@` or `$ARGUMENTS` — All arguments
+- `${@:2}` — Arguments from position 2 onwards
+- `${@:1:3}` — 3 arguments starting at position 1
+
+Disable templates with `--no-prompt-templates` or load a specific template with `--prompt-template <name>`.
+
+## Session Management
+
+Kit uses a tree-based session model that supports branching and forking conversations.
+
+### Session Locations
+
+- Default: `~/.kit/sessions/<cwd-path>/<timestamp>_<id>.jsonl`
+- Path separators in the working directory are replaced with `--` (e.g., `/home/user/project` becomes `home--user--project`)
+- Each line is a session entry (messages, tool calls, extension data)
+- Supports branching from any message to explore alternate paths
+
+### Session Commands
+
+```bash
+# Resume most recent session for current directory
+kit --continue
+kit -c
+
+# Interactive session picker
+kit --resume
+kit -r
+
+# Open specific session file
+kit --session path/to/session.jsonl
+kit -s path/to/session.jsonl
+
+# Ephemeral mode (no file persistence)
+kit --no-session
+```
+
+### Interactive Session Commands
+
+During an interactive session, use these slash commands:
+
+| Command | Description |
+|---------|-------------|
+| `/name [name]` | Set or display the session's display name |
+| `/session` | Show session info (path, ID, message count) |
+| `/resume` | Open the session picker to switch sessions |
+| `/export [path]` | Export session as JSONL (auto-generates path if omitted) |
+| `/import <path>` | Import and switch to a session from a JSONL file |
+| `/share` | Upload session to GitHub Gist and get a shareable viewer URL |
+| `/tree` | Navigate the session tree |
+| `/fork` | Branch from an earlier message |
+| `/new` | Start a fresh session |
+
+## Go SDK
+
+Embed Kit in your Go applications:
+
+```go
+package main
+
+import (
+    "context"
+    "log"
+    
+    kit "github.com/mark3labs/kit/pkg/kit"
+)
+
+func main() {
+    ctx := context.Background()
+    
+    // Create Kit instance with default configuration
+    host, err := kit.New(ctx, nil)
+    if err != nil {
+        log.Fatal(err)
+    }
+    defer host.Close()
+    
+    // Send a prompt
+    response, err := host.Prompt(ctx, "What is 2+2?")
+    if err != nil {
+        log.Fatal(err)
+    }
+    
+    println(response)
+}
+```
+
+### With Options
+
+```go
+host, err := kit.New(ctx, &kit.Options{
+    Model:        "ollama/llama3",
+    SystemPrompt: "You are a helpful bot",
+    ConfigFile:   "/path/to/config.yml",
+    MaxSteps:     10,
+    Streaming:    true,
+    Quiet:        true,
+
+    // Session options
+    SessionPath:  "./session.jsonl",  // Open specific session
+    Continue:     true,                // Resume most recent session
+    NoSession:    true,                // Ephemeral mode
+
+    // Tool options
+    ExtraTools:   []kit.Tool{...},     // Additional tools alongside defaults
+
+    // Compaction
+    AutoCompact:  true,                // Auto-compact near context limit
+
+    Debug:        true,                // Debug logging
+})
+```
+
+### With Callbacks
+
+```go
+response, err := host.PromptWithCallbacks(
+    ctx,
+    "List files in current directory",
+    func(name, args string) {
+        // Tool call started
+        println("Calling tool:", name)
+    },
+    func(name, args, result string, isError bool) {
+        // Tool call completed
+        if isError {
+            println("Tool failed:", name)
+        }
+    },
+    func(chunk string) {
+        // Streaming text chunk
+        print(chunk)
+    },
+)
+```
+
+### Session Management
+
+```go
+// Multi-turn conversations retain context automatically
+host.Prompt(ctx, "My name is Alice")
+response, _ := host.Prompt(ctx, "What's my name?")
+
+// Sessions are persisted automatically to JSONL files.
+// Access session info:
+path := host.GetSessionPath()
+id := host.GetSessionID()
+
+// Clear conversation history
+host.ClearSession()
+```
+
+Session persistence is configured via `Options`:
+
+```go
+host, _ := kit.New(ctx, &kit.Options{
+    SessionPath: "./my-session.jsonl",  // Open specific session
+    Continue:    true,                   // Resume most recent session
+    NoSession:   true,                   // Ephemeral mode
+})
+```
+
+## Advanced Usage
+
+### Subagent Pattern
+
+Spawn Kit as a subprocess for multi-agent orchestration:
+
+```bash
+kit "Analyze codebase" \
+    --json \
+    --no-session \
+    --no-extensions \
+    --quiet \
+    --model anthropic/claude-haiku-3-5-20241022
+```
+
+Parse the JSON output:
+
+```json
+{
+  "response": "Final assistant response text",
+  "model": "anthropic/claude-haiku-3-5-20241022",
+  "stop_reason": "end_turn",
+  "session_id": "a1b2c3d4e5f6",
+  "usage": {
+    "input_tokens": 1024,
+    "output_tokens": 512,
+    "total_tokens": 1536,
+    "cache_read_tokens": 0,
+    "cache_creation_tokens": 0
+  },
+  "messages": [
+    {
+      "role": "assistant",
+      "parts": [
+        {"type": "text", "data": "..."},
+        {"type": "tool_call", "data": {"name": "...", "args": "..."}},
+        {"type": "tool_result", "data": {"name": "...", "result": "..."}}
+      ]
+    }
+  ]
+}
+```
+
+### Testing with tmux
+
+Test the TUI non-interactively:
+
+```bash
+# Start Kit in detached tmux session
+tmux new-session -d -s kittest -x 120 -y 40 \
+  "kit -e ext.go --no-session 2>kit.log"
+
+# Wait for startup
+sleep 3
+
+# Capture screen
+tmux capture-pane -t kittest -p
+
+# Send input
+tmux send-keys -t kittest '/command' Enter
+
+# Cleanup
+tmux kill-session -t kittest
+```
+
+## Development
+
+### Build and Test
+
+```bash
+# Build
+go build -o output/kit ./cmd/kit
+
+# Run tests
+go test -race ./...
+
+# Run specific test
+go test -race ./cmd -run TestScriptExecution
+
+# Lint
+go vet ./...
+
+# Format
+go fmt ./...
+```
+
+### Project Structure
+
+```
+cmd/kit/             - CLI entry point (main.go)
+cmd/                 - CLI command implementations (root, auth, models, etc.)
+pkg/kit/             - Go SDK for embedding Kit
+internal/app/        - Application orchestrator (agent loop, message store, queue)
+internal/agent/      - Agent execution and tool dispatch
+internal/auth/       - OAuth authentication and credential storage
+internal/acpserver/  - ACP (Agent Client Protocol) server
+internal/clipboard/  - Cross-platform clipboard operations
+internal/compaction/ - Conversation compaction and summarization
+internal/config/     - Configuration management
+internal/core/       - Built-in tools (bash, read, write, edit, grep, find, ls)
+internal/extensions/ - Yaegi extension system
+internal/kitsetup/   - Initial setup wizard
+internal/message/    - Message content types and structured content blocks
+internal/models/     - Provider and model management
+internal/session/    - Session persistence (tree-based JSONL)
+internal/skills/     - Skill loading and system prompt composition
+internal/tools/      - MCP tool integration
+internal/ui/         - Bubble Tea TUI components
+examples/extensions/ - Example extension files
+npm/                 - NPM package wrapper for distribution
+```
+
+## Supported Providers
+
+- **Anthropic** - Claude models (native, prompt caching, OAuth)
+- **OpenAI** - GPT models
+- **Google** - Gemini models
+- **Ollama** - Local models
+- **Azure OpenAI** - Azure-hosted OpenAI
+- **AWS Bedrock** - Bedrock models
+- **Google Vertex** - Claude on Vertex AI
+- **OpenRouter** - Multi-provider router
+- **Vercel AI** - Vercel AI SDK models
+- **Custom** - Any OpenAI-compatible endpoint via `--provider-url`
+- **Auto-routed** - Any provider from models.dev database
+
+### Custom Provider
+
+Use `custom/custom` when pointing Kit at any OpenAI-compatible endpoint with `--provider-url`:
+
+```bash
+kit --provider-url "http://localhost:8080/v1" "Hello"
+```
+
+This automatically defaults to `custom/custom` without needing to specify a model. The custom provider routes through fantasy's `openaicompat` provider and supports:
+
+- Zero cost tracking (input/output = 0)
+- 262K context window, 65K output limit
+- Reasoning and temperature support
+- Optional `CUSTOM_API_KEY` environment variable or `--provider-api-key` flag
+
+### Model String Format
+
+```bash
+provider/model            # Standard format
+anthropic/claude-sonnet-latest
+openai/gpt-4o
+ollama/llama3
+google/gemini-2.0-flash-exp
+```
+
+### Model Aliases
+
+```bash
+# Anthropic Claude
+claude-opus-latest        → claude-opus-4-6
+claude-sonnet-latest      → claude-sonnet-4-6
+claude-haiku-latest       → claude-haiku-4-5
+claude-4-opus-latest      → claude-opus-4-6
+claude-4-sonnet-latest    → claude-sonnet-4-6
+claude-4-haiku-latest     → claude-haiku-4-5
+claude-3-7-sonnet-latest  → claude-3-7-sonnet-20250219
+claude-3-5-sonnet-latest   → claude-3-5-sonnet-20241022
+claude-3-5-haiku-latest   → claude-3-5-haiku-20241022
+claude-3-opus-latest      → claude-3-opus-20240229
+
+# OpenAI GPT
+o1-latest                 → o1
+o3-latest                 → o3
+o4-latest                 → o4-mini
+gpt-5-latest              → gpt-5.4
+gpt-5-chat-latest         → gpt-5.4
+gpt-4-latest              → gpt-4o
+gpt-4                     → gpt-4o
+gpt-3.5-latest            → gpt-3.5-turbo
+gpt-3.5                   → gpt-3.5-turbo
+codex-latest              → codex-mini-latest
+
+# Google Gemini
+gemini-pro-latest         → gemini-2.5-pro
+gemini-flash-latest       → gemini-2.5-flash
+gemini-flash              → gemini-2.5-flash
+gemini-pro                → gemini-2.5-pro
+```
+
+## Contributing
+
+Contributions are welcome! Please see the [contribution guide](contribute/contribute.md) for guidelines.
+
+## License
+
+[MIT](LICENSE)
+
+## Community
+
+- [Discord](https://discord.gg/RqSS2NQVsY)
+- [GitHub Issues](https://github.com/mark3labs/kit/issues)
+- [Documentation](https://github.com/mark3labs/kit/wiki)

btca.config.jsonc

@@ -64,8 +64,20 @@
       "name": "yaegi",
       "url": "https://github.com/traefik/yaegi",
       "branch": "master"
+    },
+    {
+      "type": "git",
+      "name": "acp-go-sdk",
+      "url": "https://github.com/coder/acp-go-sdk",
+      "branch": "main"
+    },
+    {
+      "type": "git",
+      "name": "opencode",
+      "url": "https://github.com/anomalyco/opencode",
+      "branch": "dev"
     }
   ],
   "model": "claude-haiku-4-5",
   "provider": "opencode"
-}
+}

cmd/acp.go

@@ -0,0 +1,159 @@
+package cmd
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"os"
+	"os/signal"
+	"syscall"
+
+	acp "github.com/coder/acp-go-sdk"
+
+	"github.com/mark3labs/kit/internal/acpserver"
+	"github.com/spf13/cobra"
+)
+
+var acpCmd = &cobra.Command{
+	Use:   "acp",
+	Short: "Start Kit as an ACP agent server",
+	Long: `Start Kit as an ACP (Agent Client Protocol) agent server.
+
+Communicates over stdio (stdin/stdout) using JSON-RPC 2.0 with
+newline-delimited JSON, compatible with OpenCode and other ACP clients.
+
+The server exposes Kit's LLM execution, tool system, and session
+management via the Agent Client Protocol. Sessions are persisted
+to Kit's standard JSONL session files.`,
+	RunE: runACP,
+}
+
+func init() {
+	rootCmd.AddCommand(acpCmd)
+}
+
+func runACP(cmd *cobra.Command, _ []string) error {
+	// Create the ACP agent implementation.
+	agent := acpserver.NewAgent()
+	defer agent.Close()
+
+	// Create the stdio connection. The SDK reads JSON-RPC from stdin and
+	// writes responses to stdout. We wrap stdin with a normalizer that
+	// fills in optional fields the SDK's generated validation requires
+	// (e.g. mcpServers) so clients that omit them still work.
+	conn := acp.NewAgentSideConnection(agent, os.Stdout, newACPNormalizer(os.Stdin))
+
+	// Wire the connection back to the agent so it can send session updates.
+	agent.SetAgentConnection(conn)
+
+	// Enable debug logging to stderr if requested.
+	if debugMode {
+		conn.SetLogger(slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
+			Level: slog.LevelDebug,
+		})))
+	}
+
+	// Wait for either the client to disconnect or a signal.
+	sigCh := make(chan os.Signal, 1)
+	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
+
+	select {
+	case <-conn.Done():
+		fmt.Fprintln(os.Stderr, "kit: ACP client disconnected")
+	case sig := <-sigCh:
+		fmt.Fprintf(os.Stderr, "kit: received %s, shutting down\n", sig)
+	}
+
+	return nil
+}
+
+// acpNormalizer wraps an io.Reader carrying newline-delimited JSON-RPC and
+// patches incoming messages so that fields the SDK validates as required —
+// but that some clients (e.g. Zed) omit — are defaulted. This avoids
+// InvalidParams errors without forking the SDK.
+type acpNormalizer struct {
+	scanner *bufio.Scanner
+	buf     bytes.Buffer // leftover bytes from the last normalized line
+}
+
+func newACPNormalizer(r io.Reader) *acpNormalizer {
+	const maxMsg = 10 * 1024 * 1024 // 10 MB, matches SDK buffer
+	s := bufio.NewScanner(r)
+	s.Buffer(make([]byte, 0, 1024*1024), maxMsg)
+	return &acpNormalizer{scanner: s}
+}
+
+// Read satisfies io.Reader. It feeds one normalized JSON line (plus newline)
+// per underlying scan, buffering across short caller reads.
+func (n *acpNormalizer) Read(p []byte) (int, error) {
+	// Drain any leftover bytes from the previous line first.
+	if n.buf.Len() > 0 {
+		return n.buf.Read(p)
+	}
+
+	if !n.scanner.Scan() {
+		if err := n.scanner.Err(); err != nil {
+			return 0, err
+		}
+		return 0, io.EOF
+	}
+
+	line := n.scanner.Bytes()
+	normalized := normalizeACPLine(line)
+	n.buf.Write(normalized)
+	n.buf.WriteByte('\n')
+	return n.buf.Read(p)
+}
+
+// normalizeACPLine ensures session/new and session/load params contain an
+// mcpServers array. Returns the original line unchanged for all other methods.
+func normalizeACPLine(line []byte) []byte {
+	// Quick check: if it already contains mcpServers, nothing to do.
+	if bytes.Contains(line, []byte(`"mcpServers"`)) {
+		return line
+	}
+
+	// Only bother parsing if the method could be session/new or session/load.
+	if !bytes.Contains(line, []byte(`"session/new"`)) &&
+		!bytes.Contains(line, []byte(`"session/load"`)) {
+		return line
+	}
+
+	var msg struct {
+		JSONRPC string          `json:"jsonrpc"`
+		ID      json.RawMessage `json:"id,omitempty"`
+		Method  string          `json:"method"`
+		Params  json.RawMessage `json:"params,omitempty"`
+	}
+	if err := json.Unmarshal(line, &msg); err != nil {
+		return line
+	}
+	if msg.Method != "session/new" && msg.Method != "session/load" {
+		return line
+	}
+
+	// Patch params to include mcpServers: [].
+	var params map[string]json.RawMessage
+	if err := json.Unmarshal(msg.Params, &params); err != nil {
+		return line
+	}
+	if _, ok := params["mcpServers"]; ok {
+		return line
+	}
+	params["mcpServers"] = json.RawMessage(`[]`)
+
+	patched, err := json.Marshal(params)
+	if err != nil {
+		return line
+	}
+	msg.Params = patched
+
+	out, err := json.Marshal(msg)
+	if err != nil {
+		return line
+	}
+	return out
+}

cmd/auth.go

@@ -1,11 +1,15 @@
 package cmd
 
 import (
-	"bufio"
+	"context"
 	"fmt"
+	"net"
+	"net/http"
 	"os"
 	"strings"
+	"time"
 
+	"charm.land/huh/v2"
 	"github.com/mark3labs/kit/internal/auth"
 	kit "github.com/mark3labs/kit/pkg/kit"
 	"github.com/spf13/cobra"
@@ -14,7 +18,7 @@ import (
 // authCmd represents the auth command for managing AI provider authentication.
 // This command provides subcommands for login, logout, and status checking
 // of authentication credentials for various AI providers, with OAuth support
-// for providers like Anthropic.
+// for providers like Anthropic and OpenAI.
 var authCmd = &cobra.Command{
 	Use:   "auth",
 	Short: "Manage authentication credentials for AI providers",
@@ -25,9 +29,11 @@ using OAuth flows. Stored credentials take precedence over environment variables
 
 Available providers:
   - anthropic: Anthropic Claude API (OAuth)
+  - openai:    OpenAI API (OAuth and API key)
 
 Examples:
   kit auth login anthropic
+  kit auth login openai
   kit auth logout anthropic
   kit auth status`,
 }
@@ -46,9 +52,11 @@ environment variables when making API calls.
 
 Available providers:
   - anthropic: Anthropic Claude API (OAuth)
+  - openai:    OpenAI ChatGPT Plus/Pro (Codex OAuth)
 
 Example:
-  kit auth login anthropic`,
+  kit auth login anthropic
+  kit auth login openai`,
 	Args: cobra.ExactArgs(1),
 	RunE: runAuthLogin,
 }
@@ -61,14 +69,16 @@ var authLogoutCmd = &cobra.Command{
 	Short: "Remove stored authentication credentials for a provider",
 	Long: `Remove stored authentication credentials for an AI provider.
 
-This will delete the stored API key for the specified provider. You will need
-to use environment variables or command-line flags for authentication after logout.
+This will delete the stored API key or OAuth credentials for the specified provider. 
+You will need to use environment variables or command-line flags for authentication after logout.
 
 Available providers:
   - anthropic: Anthropic Claude API
+  - openai:    OpenAI API
 
 Example:
-  kit auth logout anthropic`,
+  kit auth logout anthropic
+  kit auth logout openai`,
 	Args: cobra.ExactArgs(1),
 	RunE: runAuthLogout,
 }
@@ -101,8 +111,10 @@ func runAuthLogin(cmd *cobra.Command, args []string) error {
 	switch provider {
 	case "anthropic":
 		return loginAnthropic()
+	case "openai":
+		return loginOpenAI()
 	default:
-		return fmt.Errorf("unsupported provider: %s. Available providers: anthropic", provider)
+		return fmt.Errorf("unsupported provider: %s. Available providers: anthropic, openai", provider)
 	}
 }
 
@@ -112,8 +124,10 @@ func runAuthLogout(cmd *cobra.Command, args []string) error {
 	switch provider {
 	case "anthropic":
 		return logoutAnthropic()
+	case "openai":
+		return logoutOpenAI()
 	default:
-		return fmt.Errorf("unsupported provider: %s. Available providers: anthropic", provider)
+		return fmt.Errorf("unsupported provider: %s. Available providers: anthropic, openai", provider)
 	}
 }
 
@@ -157,8 +171,44 @@ func runAuthStatus(cmd *cobra.Command, args []string) error {
 		}
 	}
 
+	// Check OpenAI credentials
+	fmt.Print("\nOpenAI: ")
+	if hasOpenAICreds, err := cm.HasOpenAICredentials(); err != nil {
+		fmt.Printf("Error checking credentials: %v\n", err)
+	} else if hasOpenAICreds {
+		if creds, err := cm.GetOpenAICredentials(); err != nil {
+			fmt.Printf("Error reading credentials: %v\n", err)
+		} else {
+			authType := "API Key"
+			status := "✓ Authenticated"
+
+			if creds.Type == "oauth" {
+				authType = "OAuth (ChatGPT/Codex)"
+				if creds.IsExpired() {
+					status = "⚠️  Token expired (will refresh automatically)"
+				} else if creds.NeedsRefresh() {
+					status = "⚠️  Token expires soon (will refresh automatically)"
+				}
+			}
+
+			accountInfo := ""
+			if creds.Type == "oauth" && creds.AccountID != "" {
+				accountInfo = fmt.Sprintf(" [%s]", creds.AccountID)
+			}
+
+			fmt.Printf("%s (%s%s, stored %s)\n", status, authType, accountInfo, creds.CreatedAt.Format("2006-01-02 15:04:05"))
+		}
+	} else {
+		fmt.Println("✗ Not authenticated")
+		// Check if environment variable is set
+		if os.Getenv("OPENAI_API_KEY") != "" {
+			fmt.Println("  (OPENAI_API_KEY environment variable is set)")
+		}
+	}
+
 	fmt.Println("\nTo authenticate with a provider:")
 	fmt.Println("  kit auth login anthropic")
+	fmt.Println("  kit auth login openai")
 
 	return nil
 }
@@ -171,14 +221,15 @@ func loginAnthropic() error {
 
 	// Check if already authenticated
 	if hasAuth, err := cm.HasAnthropicCredentials(); err == nil && hasAuth {
-		fmt.Print("You are already authenticated with Anthropic. Do you want to re-authenticate? (y/N): ")
-		reader := bufio.NewReader(os.Stdin)
-		response, err := reader.ReadString('\n')
-		if err != nil {
-			return fmt.Errorf("failed to read response: %w", err)
-		}
-		response = strings.TrimSpace(strings.ToLower(response))
-		if response != "y" && response != "yes" {
+		var reauth bool
+		err := huh.NewConfirm().
+			Title("You are already authenticated with Anthropic").
+			Description("Do you want to re-authenticate?").
+			Affirmative("Yes").
+			Negative("No").
+			Value(&reauth).
+			Run()
+		if err != nil || !reauth {
 			fmt.Println("Authentication cancelled.")
 			return nil
 		}
@@ -204,10 +255,13 @@ func loginAnthropic() error {
 
 	// Wait for user to complete OAuth flow
 	fmt.Println("After authorizing the application, you'll receive an authorization code.")
-	fmt.Print("Please enter the authorization code: ")
 
-	reader := bufio.NewReader(os.Stdin)
-	code, err := reader.ReadString('\n')
+	var code string
+	err = huh.NewInput().
+		Title("Authorization code").
+		Description("Paste the code from your browser").
+		Value(&code).
+		Run()
 	if err != nil {
 		return fmt.Errorf("failed to read authorization code: %w", err)
 	}
@@ -255,15 +309,15 @@ func logoutAnthropic() error {
 	}
 
 	// Confirm logout
-	fmt.Print("Are you sure you want to remove your Anthropic credentials? (y/N): ")
-	reader := bufio.NewReader(os.Stdin)
-	response, err := reader.ReadString('\n')
-	if err != nil {
-		return fmt.Errorf("failed to read response: %w", err)
-	}
-
-	response = strings.TrimSpace(strings.ToLower(response))
-	if response != "y" && response != "yes" {
+	var confirm bool
+	err = huh.NewConfirm().
+		Title("Remove Anthropic credentials").
+		Description("Are you sure you want to remove your stored credentials?").
+		Affirmative("Yes").
+		Negative("No").
+		Value(&confirm).
+		Run()
+	if err != nil || !confirm {
 		fmt.Println("Logout cancelled.")
 		return nil
 	}
@@ -278,3 +332,246 @@ func logoutAnthropic() error {
 
 	return nil
 }
+
+func loginOpenAI() error {
+	cm, err := kit.NewCredentialManager()
+	if err != nil {
+		return fmt.Errorf("failed to initialize credential manager: %w", err)
+	}
+
+	// Check if already authenticated
+	if hasAuth, err := cm.HasOpenAICredentials(); err == nil && hasAuth {
+		var reauth bool
+		err := huh.NewConfirm().
+			Title("You are already authenticated with OpenAI (ChatGPT/Codex)").
+			Description("Do you want to re-authenticate?").
+			Affirmative("Yes").
+			Negative("No").
+			Value(&reauth).
+			Run()
+		if err != nil || !reauth {
+			fmt.Println("Authentication cancelled.")
+			return nil
+		}
+	}
+
+	// Create OAuth client
+	client := auth.NewOpenAIOAuthClient()
+
+	// Generate authorization URL
+	fmt.Println("🔐 Starting OAuth authentication with OpenAI (ChatGPT/Codex)...")
+	fmt.Println("This will open your browser to authenticate with your ChatGPT account.")
+	fmt.Println()
+
+	authData, err := client.GetAuthorizationURL()
+	if err != nil {
+		return fmt.Errorf("failed to generate authorization URL: %w", err)
+	}
+
+	// Start local callback server
+	callbackServer, err := startOpenAICallbackServer(authData.State)
+	if err != nil {
+		fmt.Printf("⚠️  Could not start local callback server: %v\n", err)
+		fmt.Println("Falling back to manual code entry.")
+	}
+	if callbackServer != nil {
+		defer callbackServer.Close()
+	}
+
+	// Display URL and try to open browser
+	fmt.Println("📱 Opening your browser for authentication...")
+	fmt.Println("If the browser doesn't open automatically, please visit this URL:")
+	fmt.Printf("\n%s\n\n", authData.URL)
+
+	// Try to open browser
+	auth.TryOpenBrowser(authData.URL)
+
+	// Wait for callback or manual input
+	var code string
+	if callbackServer != nil {
+		fmt.Println("Waiting for browser authentication...")
+		select {
+		case callbackCode := <-callbackServer.CodeChan:
+			if callbackCode != "" {
+				code = callbackCode
+				fmt.Println("✓ Received authorization code from browser callback.")
+			}
+		case <-time.After(2 * time.Minute):
+			fmt.Println("\n⏱️  Timeout waiting for browser callback.")
+			callbackServer.Close()
+		}
+	}
+
+	// If no code from callback, prompt for manual entry
+	if code == "" {
+		fmt.Println("\nAfter authorizing, paste the callback URL or authorization code below.")
+		fmt.Println("(The callback URL will look like: http://localhost:1455/auth/callback?code=...&state=...)")
+		fmt.Println()
+
+		var input string
+		err = huh.NewInput().
+			Title("Callback URL or Code").
+			Description("Paste the full callback URL or just the authorization code").
+			Value(&input).
+			Run()
+		if err != nil {
+			return fmt.Errorf("failed to read input: %w", err)
+		}
+		input = strings.TrimSpace(input)
+
+		if input == "" {
+			return fmt.Errorf("authorization code cannot be empty")
+		}
+
+		// Parse the input (could be full URL or just code)
+		parsedCode, parsedState := auth.ParseOpenAIAuthorizationInput(input)
+		if parsedCode == "" {
+			return fmt.Errorf("could not extract authorization code from input")
+		}
+
+		// Validate state if provided
+		if parsedState != "" && parsedState != authData.State {
+			return fmt.Errorf("state mismatch - possible security issue")
+		}
+		code = parsedCode
+	}
+
+	// Exchange code for tokens
+	fmt.Println("\n🔄 Exchanging authorization code for access token...")
+	creds, err := client.ExchangeCode(code, authData.Verifier)
+	if err != nil {
+		return fmt.Errorf("failed to exchange authorization code: %w", err)
+	}
+
+	// Store the credentials
+	if err := cm.SetOpenAIOAuthCredentials(creds); err != nil {
+		return fmt.Errorf("failed to store credentials: %w", err)
+	}
+
+	fmt.Println("✅ Successfully authenticated with OpenAI (ChatGPT/Codex)!")
+	fmt.Printf("📁 Credentials stored in: %s\n", cm.GetCredentialsPath())
+	fmt.Printf("👤 Account ID: %s\n", creds.AccountID)
+	fmt.Println("\n🎉 Your OAuth credentials will now be used for OpenAI API calls.")
+	fmt.Println("💡 You can check your authentication status with: kit auth status")
+
+	return nil
+}
+
+// callbackServer holds the HTTP server and channel for receiving the OAuth callback
+type callbackServer struct {
+	Server   *http.Server
+	CodeChan chan string
+	State    string
+}
+
+// Close shuts down the callback server
+func (cs *callbackServer) Close() {
+	if cs.Server != nil {
+		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer cancel()
+		_ = cs.Server.Shutdown(ctx)
+	}
+}
+
+// startOpenAICallbackServer starts a local HTTP server to receive the OAuth callback
+func startOpenAICallbackServer(expectedState string) (*callbackServer, error) {
+	codeChan := make(chan string, 1)
+
+	mux := http.NewServeMux()
+	server := &http.Server{
+		Addr:    "127.0.0.1:1455",
+		Handler: mux,
+	}
+
+	mux.HandleFunc("/auth/callback", func(w http.ResponseWriter, r *http.Request) {
+		// Check state
+		state := r.URL.Query().Get("state")
+		if state != expectedState {
+			http.Error(w, "State mismatch", http.StatusBadRequest)
+			return
+		}
+
+		code := r.URL.Query().Get("code")
+		if code == "" {
+			http.Error(w, "Missing authorization code", http.StatusBadRequest)
+			return
+		}
+
+		// Send code to channel
+		select {
+		case codeChan <- code:
+		default:
+		}
+
+		// Return success page
+		w.Header().Set("Content-Type", "text/html")
+		w.WriteHeader(http.StatusOK)
+		_, _ = fmt.Fprintf(w, `<!DOCTYPE html>
+<html>
+<head><title>Authentication Successful</title></head>
+<body style="font-family: sans-serif; text-align: center; padding: 50px;">
+<h1>✓ Authentication Successful</h1>
+<p>You can close this window and return to the terminal.</p>
+</body>
+</html>`)
+	})
+
+	// Try to start server
+	listener, err := net.Listen("tcp", "127.0.0.1:1455")
+	if err != nil {
+		return nil, fmt.Errorf("port 1455 not available: %w", err)
+	}
+	_ = listener.Close()
+
+	go func() {
+		_ = server.ListenAndServe()
+	}()
+
+	return &callbackServer{
+		Server:   server,
+		CodeChan: codeChan,
+		State:    expectedState,
+	}, nil
+}
+
+func logoutOpenAI() error {
+	cm, err := kit.NewCredentialManager()
+	if err != nil {
+		return fmt.Errorf("failed to initialize credential manager: %w", err)
+	}
+
+	// Check if authenticated
+	hasAuth, err := cm.HasOpenAICredentials()
+	if err != nil {
+		return fmt.Errorf("failed to check authentication status: %w", err)
+	}
+
+	if !hasAuth {
+		fmt.Println("You are not currently authenticated with OpenAI.")
+		return nil
+	}
+
+	// Confirm logout
+	var confirm bool
+	err = huh.NewConfirm().
+		Title("Remove OpenAI credentials").
+		Description("Are you sure you want to remove your stored credentials?").
+		Affirmative("Yes").
+		Negative("No").
+		Value(&confirm).
+		Run()
+	if err != nil || !confirm {
+		fmt.Println("Logout cancelled.")
+		return nil
+	}
+
+	// Remove credentials
+	if err := cm.RemoveOpenAICredentials(); err != nil {
+		return fmt.Errorf("failed to remove credentials: %w", err)
+	}
+
+	fmt.Println("✓ Successfully logged out from OpenAI!")
+	fmt.Println("You will need to use environment variables or command-line flags for authentication.")
+
+	return nil
+}

cmd/install.go

@@ -0,0 +1,225 @@
+package cmd
+
+import (
+	"fmt"
+	"os/exec"
+
+	"github.com/charmbracelet/log"
+	"github.com/mark3labs/kit/internal/extensions"
+	"github.com/spf13/cobra"
+)
+
+var (
+	installLocalFlag     bool
+	installUpdateFlag    bool
+	installUninstallFlag bool
+	installAllFlag       bool
+)
+
+var installCmd = &cobra.Command{
+	Use:   "install <git-url>",
+	Short: "Install extensions from git repositories",
+	Long: `Install extensions from git repositories.
+
+The install command downloads and installs Kit extensions from git repositories.
+Extensions are stored in the global extensions directory by default, or in the
+project's .kit/git/ directory when using the --local flag.
+
+When a repo contains multiple extensions, an interactive multi-select is shown
+so you can choose which to install. Use --all to skip selection and install everything.
+
+Supported URL formats:
+  - github.com/user/repo (shorthand, defaults to HTTPS)
+  - git:github.com/user/repo
+  - https://github.com/user/repo
+  - ssh://git@github.com/user/repo
+  - git@github.com:user/repo
+
+You can pin to a specific version, tag, or commit using @:
+  - github.com/user/repo@v1.0.0
+  - github.com/user/repo@main
+  - github.com/user/repo@abc1234
+
+Examples:
+  kit install github.com/user/my-extension
+  kit install github.com/user/my-extension@v1.0.0
+  kit install github.com/user/my-extension --local
+  kit install github.com/user/collection --all`,
+	Args: cobra.ExactArgs(1),
+	RunE: runInstall,
+}
+
+func init() {
+	installCmd.Flags().BoolVarP(&installLocalFlag, "local", "l", false, "Install to project-local .kit/git/ directory")
+	installCmd.Flags().BoolVarP(&installUpdateFlag, "update", "u", false, "Update an already-installed package")
+	installCmd.Flags().BoolVar(&installUninstallFlag, "uninstall", false, "Remove an installed package")
+	installCmd.Flags().BoolVar(&installAllFlag, "all", false, "Install all extensions without prompting")
+
+	rootCmd.AddCommand(installCmd)
+}
+
+func runInstall(cmd *cobra.Command, args []string) error {
+	sourceStr := args[0]
+
+	// Check that git is available
+	if _, err := exec.LookPath("git"); err != nil {
+		return fmt.Errorf("git is not installed or not in PATH")
+	}
+
+	// Parse the source
+	source, err := extensions.ParseGitSource(sourceStr)
+	if err != nil {
+		return fmt.Errorf("invalid source: %w", err)
+	}
+
+	// Determine scope
+	scope := extensions.ScopeGlobal
+	if installLocalFlag {
+		scope = extensions.ScopeProject
+	}
+
+	installer := extensions.NewInstaller(".")
+
+	// Handle uninstall
+	if installUninstallFlag {
+		return runUninstall(installer, source, scope)
+	}
+
+	// Handle update
+	if installUpdateFlag {
+		return runUpdate(installer, source, scope)
+	}
+
+	// Handle install
+	return runInstallPackage(installer, source, scope)
+}
+
+func runInstallPackage(installer *extensions.Installer, source *extensions.GitSource, scope extensions.InstallScope) error {
+	// Check if already installed
+	existingScope, installed := installer.IsInstalled(source)
+	if installed {
+		return fmt.Errorf("extension already installed (scope: %s). Use --update to update or --uninstall to remove", existingScope)
+	}
+
+	// Preview extensions to decide if we need multi-select
+	previews, tempDir, err := installer.PreviewExtensions(source)
+	if err != nil {
+		return fmt.Errorf("previewing extensions: %w", err)
+	}
+	defer extensions.CleanupTempDir(tempDir)
+
+	if len(previews) == 0 {
+		return fmt.Errorf("no extensions found in %s", source.String())
+	}
+
+	scopeStr := "globally"
+	if scope == extensions.ScopeProject {
+		scopeStr = "locally in .kit/git/"
+	}
+
+	// Single extension or --all flag: install everything directly
+	if len(previews) == 1 || installAllFlag {
+		if err := installer.Install(source, scope); err != nil {
+			return fmt.Errorf("install failed: %w", err)
+		}
+
+		if source.Pinned {
+			fmt.Printf("Installed %s at %s %s\n", source.String(), source.Ref, scopeStr)
+		} else {
+			fmt.Printf("Installed %d extension(s) from %s %s\n", len(previews), source.String(), scopeStr)
+		}
+
+		log.Info("extension installed", "source", source.String(), "scope", scope)
+		return nil
+	}
+
+	// Multiple extensions: show interactive selection
+	includePaths, err := multiSelectForInstall(previews)
+	if err != nil {
+		if err.Error() == "selection cancelled" || err.Error() == "no extensions selected" {
+			fmt.Println("Install cancelled.")
+			return nil
+		}
+		return fmt.Errorf("selection failed: %w", err)
+	}
+
+	if err := installer.InstallWithInclude(source, scope, includePaths); err != nil {
+		return fmt.Errorf("install failed: %w", err)
+	}
+
+	fmt.Printf("Installed %d extension(s) from %s %s\n", len(includePaths), source.String(), scopeStr)
+	for _, path := range includePaths {
+		fmt.Printf("  - %s\n", path)
+	}
+
+	log.Info("extension installed", "source", source.String(), "scope", scope, "selected", len(includePaths))
+	return nil
+}
+
+func runUpdate(installer *extensions.Installer, source *extensions.GitSource, scope extensions.InstallScope) error {
+	// Find the installed package
+	existingScope, installed := installer.IsInstalled(source)
+	if !installed {
+		// Try to find with wildcard (no version)
+		entry, foundScope, err := extensions.FindInManifest(source.Identity())
+		if err != nil || entry == nil {
+			return fmt.Errorf("extension not installed: %s", source.Identity())
+		}
+		// Parse the found entry's source
+		foundSource, err := extensions.ParseGitSource(entry.Source)
+		if err != nil {
+			return fmt.Errorf("failed to parse installed source: %w", err)
+		}
+		existingScope = foundScope
+		source = foundSource
+	}
+
+	// Override scope if specified
+	if installLocalFlag && scope != existingScope {
+		return fmt.Errorf("extension installed in %s scope, cannot update with --local flag", existingScope)
+	}
+	scope = existingScope
+
+	// Check if pinned
+	if source.Pinned {
+		fmt.Printf("Skipping %s (pinned at %s)\n", source.Identity(), source.Ref)
+		return nil
+	}
+
+	// Update
+	if err := installer.Update(source, scope); err != nil {
+		return fmt.Errorf("update failed: %w", err)
+	}
+
+	fmt.Printf("Updated %s\n", source.Identity())
+	log.Info("extension updated", "source", source.Identity(), "scope", scope)
+	return nil
+}
+
+func runUninstall(installer *extensions.Installer, source *extensions.GitSource, scope extensions.InstallScope) error {
+	// Find where it's installed (ignore scope flag for uninstall - remove from wherever it exists)
+	existingScope, installed := installer.IsInstalled(source)
+	if !installed {
+		// Try to find in manifests
+		entry, foundScope, err := extensions.FindInManifest(source.Identity())
+		if err != nil || entry == nil {
+			return fmt.Errorf("extension not installed: %s", source.Identity())
+		}
+		existingScope = foundScope
+		// Parse the found entry's source
+		foundSource, err := extensions.ParseGitSource(entry.Source)
+		if err != nil {
+			return fmt.Errorf("failed to parse installed source: %w", err)
+		}
+		source = foundSource
+	}
+
+	// Uninstall from the scope where it's installed
+	if err := installer.Uninstall(source, existingScope); err != nil {
+		return fmt.Errorf("uninstall failed: %w", err)
+	}
+
+	fmt.Printf("Uninstalled %s from %s scope\n", source.Identity(), existingScope)
+	log.Info("extension uninstalled", "source", source.Identity(), "scope", existingScope)
+	return nil
+}

cmd/install_multiselect.go

@@ -0,0 +1,70 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	"charm.land/huh/v2"
+	"github.com/charmbracelet/log"
+	"github.com/mark3labs/kit/internal/extensions"
+)
+
+// multiSelectForInstall runs a multi-select prompt for extension selection.
+// Returns the selected extension paths, or an error if cancelled.
+func multiSelectForInstall(previews []extensions.ExtensionPreview) ([]string, error) {
+	if len(previews) == 0 {
+		return nil, fmt.Errorf("no extensions to select")
+	}
+
+	// Non-interactive: select all
+	if !isInteractive() {
+		log.Info("Non-interactive mode, selecting all extensions")
+		paths := make([]string, len(previews))
+		for i, p := range previews {
+			paths[i] = p.Path
+		}
+		return paths, nil
+	}
+
+	// Single extension: just return it
+	if len(previews) == 1 {
+		return []string{previews[0].Path}, nil
+	}
+
+	// Build options for huh MultiSelect
+	options := make([]huh.Option[string], len(previews))
+	for i, p := range previews {
+		label := fmt.Sprintf("%s  %s", p.Name, p.Path)
+		options[i] = huh.NewOption(label, p.Path).Selected(true)
+	}
+
+	var selected []string
+
+	form := huh.NewForm(
+		huh.NewGroup(
+			huh.NewMultiSelect[string]().
+				Title("Select extensions to install").
+				Options(options...).
+				Value(&selected),
+		),
+	)
+
+	if err := form.Run(); err != nil {
+		return nil, fmt.Errorf("selection cancelled")
+	}
+
+	if len(selected) == 0 {
+		return nil, fmt.Errorf("no extensions selected")
+	}
+
+	return selected, nil
+}
+
+// isInteractive checks if the terminal is interactive.
+func isInteractive() bool {
+	fi, err := os.Stdout.Stat()
+	if err != nil {
+		return false
+	}
+	return (fi.Mode() & os.ModeCharDevice) != 0
+}

cmd/models.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"sort"
 
+	"github.com/mark3labs/kit/internal/models"
 	kit "github.com/mark3labs/kit/pkg/kit"
 	"github.com/spf13/cobra"
 )
@@ -47,6 +48,9 @@ func runModels(_ *cobra.Command, args []string) error {
 }
 
 func printAllProviders(showAll bool) error {
+	// Reload the registry to pick up any custom models from config
+	models.ReloadGlobalRegistry()
+
 	var providerIDs []string
 	if showAll {
 		providerIDs = kit.GetSupportedProviders()
@@ -98,6 +102,9 @@ func printAllProviders(showAll bool) error {
 }
 
 func printProvider(provider string) error {
+	// Reload the registry to pick up any custom models from config
+	models.ReloadGlobalRegistry()
+
 	m, err := kit.GetModelsForProvider(provider)
 	if err != nil {
 		return fmt.Errorf("unknown provider %q. Run 'kit models' to see all providers", provider)

cmd/skill.go

@@ -0,0 +1,58 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+
+	"github.com/spf13/cobra"
+)
+
+// skillCmd installs Kit skills via the skills.sh CLI (npx skills).
+var skillCmd = &cobra.Command{
+	Use:   "skill",
+	Short: "Install Kit skills via skills.sh",
+	Long: `Install Kit skills that teach AI agents how to build with Kit.
+Uses the skills.sh CLI (npx skills) to install all skills from the Kit repository.
+
+Two skills are provided:
+
+  1. Extensions — creating Kit extensions with full knowledge of the extension
+     API, lifecycle events, widgets, tools, commands, editor interceptors,
+     tool renderers, and Yaegi interpreter constraints.
+
+  2. SDK — building AI-powered applications with the Kit Go SDK, including
+     providers, agents, tools, and MCP integration.
+
+Example:
+  kit skill`,
+	RunE: runSkill,
+}
+
+func init() {
+	rootCmd.AddCommand(skillCmd)
+}
+
+func runSkill(_ *cobra.Command, _ []string) error {
+	npx, err := exec.LookPath("npx")
+	if err != nil {
+		return fmt.Errorf("npx not found in PATH — install Node.js to use this command: %w", err)
+	}
+
+	args := []string{
+		"skills",
+		"add",
+		"mark3labs/kit",
+	}
+
+	cmd := exec.Command(npx, args...)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("skills install failed: %w", err)
+	}
+
+	return nil
+}

examples/extensions/README.md

@@ -0,0 +1,197 @@
+# Kit Extension Examples
+
+A collection of example extensions demonstrating various Kit capabilities. These can be installed individually or as a complete collection.
+
+## Installation
+
+### Install all examples
+```bash
+kit install github.com/mark3labs/kit/examples/extensions
+```
+
+### Install with interactive selection
+```bash
+kit install github.com/mark3labs/kit/examples/extensions --select
+```
+
+### Install locally in your project
+```bash
+kit install github.com/mark3labs/kit/examples/extensions --local
+```
+
+## Extension Index
+
+### Core Concepts
+
+| Extension | Description | Key API |
+|-----------|-------------|---------|
+| `minimal.go` | Minimal viable extension | Basic `Init()` function |
+| `plan-mode.go` | Restrict agent to read-only tools | `OnBeforeAgentStart`, `SetActiveTools` |
+| `tool-logger.go` | Log all tool calls to file | `OnToolCall`, `OnToolResult` |
+| `notify.go` | Display notifications | `PrintInfo`, `PrintBlock` |
+
+### UI & Widgets
+
+| Extension | Description | Key API |
+|-----------|-------------|---------|
+| `widget-status.go` | Persistent status widget | `SetWidget`, `RemoveWidget` |
+| `header-footer-demo.go` | Custom header/footer | `SetHeader`, `SetFooter` |
+| `overlay-demo.go` | Modal overlay dialogs | `ShowOverlay` |
+| `compact-notify.go` | Compact mode notifications | `PrintBlock` |
+| `branded-output.go` | Custom styled output | `PrintBlock` with colors |
+
+### Input & Editor
+
+| Extension | Description | Key API |
+|-----------|-------------|---------|
+| `custom-editor-demo.go` | Custom key handling | `SetEditor`, `EditorKeyAction` |
+| `pirate.go` | Transform user input | `OnInput`, `InputResult` |
+| `interactive-shell.go` | Custom command input | Slash commands with prompts |
+| `inline-bash.go` | Execute bash inline | Input handling, `exec` |
+
+### Session & Context
+
+| Extension | Description | Key API |
+|-----------|-------------|---------|
+| `context-inject.go` | Inject context into prompts | `OnContextPrepare` |
+| `bookmark.go` | Bookmark messages | `AppendEntry`, `GetEntries` |
+| `project-rules.go` | Project-specific rules | Session data, file reading |
+| `protected-paths.go` | Block dangerous operations | `OnToolCall` with blocking |
+| `permission-gate.go` | Confirm destructive actions | `OnToolCall` with confirmation |
+
+### Tools & Commands
+
+| Extension | Description | Key API |
+|-----------|-------------|---------|
+| `auto-commit.go` | Auto-commit changes | Custom tool, git operations |
+| `summarize.go` | Summarize conversation | Custom tool with parameters |
+| `confirm-destructive.go` | Confirm destructive commands | `OnToolCall` blocking |
+| `lsp-diagnostics.go` | LSP integration | Complex extension, external process |
+
+### Subagents & Background Tasks
+
+| Extension | Description | Key API |
+|-----------|-------------|---------|
+| `kit-kit.go` | Spawn Kit as subagent | Subagent spawning |
+| `subagent-test.go` | Test subagent functionality | `SpawnSubagent` |
+| `subagent-widget.go` | Widget with subagent updates | Goroutines + widgets |
+| `dev-reload.go` | Hot reload extensions | `ReloadExtensions` |
+
+### Integrations
+
+| Extension | Description | Key API |
+|-----------|-------------|---------|
+| `kit-telegram/` | Telegram relay for remote monitoring & control | `RegisterCommand`, `OnAgentStart/End`, `SetStatus`, `SendMessage` |
+
+### Themes
+
+| Extension | Description | Key API |
+|-----------|-------------|---------|
+| `neon-theme.go` | Register and switch custom themes | `RegisterTheme`, `SetTheme` |
+
+### Rendering
+
+| Extension | Description | Key API |
+|-----------|-------------|---------|
+| `tool-renderer-demo.go` | Custom tool output styling | `RegisterToolRenderer` |
+| `prompt-demo.go` | Interactive prompts | `PromptSelect`, `PromptConfirm` |
+
+## Extension Details
+
+### minimal.go
+The bare minimum extension showing the required structure:
+- Package `main`
+- Import `kit/ext`
+- Export `Init(api ext.API)` function
+
+### plan-mode.go
+A complete example demonstrating:
+- Slash command (`/plan`)
+- Keyboard shortcut (`ctrl+alt+p`)
+- Option registration
+- Status bar indicators
+- System prompt injection
+- Tool filtering
+
+### widget-status.go
+Shows how to create persistent UI elements:
+- Create widgets with `SetWidget`
+- Update content dynamically
+- Remove when done
+- Handle session lifecycle
+
+### context-inject.go
+Advanced context manipulation:
+- Read project files
+- Inject into LLM context
+- Filter messages
+- Use negative indices for ephemeral content
+
+### lsp-diagnostics.go
+Complex real-world example:
+- Multi-file extension
+- External process management (LSP server)
+- File watching
+- Diagnostics aggregation
+
+### kit-telegram/
+Full-featured Telegram integration:
+- Slash command with subcommands and tab completion
+- Interactive guided setup flow with prompts
+- Background long-polling goroutine
+- Progress message rendering edited in place
+- Message queue with edit-before-dispatch
+- Remote command handling from Telegram
+- Status bar and widget updates
+- Config persistence with atomic writes
+
+## Multi-File Extension Example
+
+The `kit-kit-agents/` directory demonstrates the multi-file pattern:
+
+```
+kit-kit-agents/
+├── main.go          # Entry point with Init()
+├── agent.go         # Agent configuration
+├── manager.go       # Agent lifecycle management
+└── README.md        # Documentation
+```
+
+When the repo is installed, all files in subdirectories with `main.go` are loaded as separate extensions.
+
+## Testing & Validation
+
+After installing, test the extensions:
+
+```bash
+# List all loaded extensions
+kit extensions list
+
+# Validate all extensions
+kit extensions validate
+
+# Run with a specific extension
+kit -e ~/.local/share/kit/git/github.com/mark3labs/kit/examples/extensions/plan-mode.go
+```
+
+## Creating Your Own
+
+1. Copy `minimal.go` as a starting point
+2. Modify the `Init()` function to register your handlers
+3. Use the other examples for reference on specific APIs
+4. Test with `kit -e your-extension.go`
+5. Share by pushing to a git repository!
+
+## Update
+
+To get the latest examples:
+
+```bash
+kit install github.com/mark3labs/kit/examples/extensions --update
+```
+
+## See Also
+
+- [Kit Extensions Guide](https://github.com/mark3labs/kit/blob/main/.agents/skills/kit-extensions/SKILL.md)
+- [API Reference](https://github.com/mark3labs/kit/blob/main/internal/extensions/api.go)
+- [Example Extensions Source](https://github.com/mark3labs/kit/tree/main/examples/extensions)

examples/extensions/auto-commit.go

@@ -0,0 +1,70 @@
+//go:build ignore
+
+package main
+
+import (
+	"os/exec"
+	"strings"
+
+	"kit/ext"
+)
+
+// Init automatically commits staged changes when the session shuts down,
+// using the last assistant message as the commit message.
+//
+// Only commits if:
+//   - There are staged changes (git diff --cached is non-empty)
+//   - There is at least one assistant message to use as commit message
+//
+// The commit message is derived from the last assistant response, trimmed
+// to the first paragraph (max 72 chars for the subject line).
+//
+// Usage: kit -e examples/extensions/auto-commit.go
+func Init(api ext.API) {
+	api.OnSessionShutdown(func(_ ext.SessionShutdownEvent, ctx ext.Context) {
+		// Check for staged changes.
+		err := exec.Command("git", "diff", "--cached", "--quiet").Run()
+		if err == nil {
+			return // exit code 0 means no staged changes
+		}
+
+		// Get the last assistant message.
+		msgs := ctx.GetMessages()
+		var lastAssistant string
+		for i := len(msgs) - 1; i >= 0; i-- {
+			if msgs[i].Role == "assistant" {
+				lastAssistant = msgs[i].Content
+				break
+			}
+		}
+		if lastAssistant == "" {
+			return
+		}
+
+		// Build commit message: first paragraph, subject line max 72 chars.
+		subject := firstParagraph(lastAssistant)
+		if len(subject) > 72 {
+			subject = subject[:69] + "..."
+		}
+
+		// Commit.
+		cmd := exec.Command("git", "commit", "-m", subject)
+		output, err := cmd.CombinedOutput()
+		if err != nil {
+			ctx.PrintError("Auto-commit failed: " + string(output))
+			return
+		}
+		ctx.PrintInfo("Auto-committed: " + subject)
+	})
+}
+
+// firstParagraph returns the first non-empty paragraph of text.
+func firstParagraph(text string) string {
+	text = strings.TrimSpace(text)
+	// Split on double newlines (paragraph breaks).
+	parts := strings.SplitN(text, "\n\n", 2)
+	line := strings.TrimSpace(parts[0])
+	// Collapse to single line.
+	line = strings.ReplaceAll(line, "\n", " ")
+	return line
+}

examples/extensions/bookmark.go

@@ -0,0 +1,101 @@
+//go:build ignore
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+	"time"
+
+	"kit/ext"
+)
+
+// Init adds bookmark commands for marking and recalling important points in
+// a conversation. Bookmarks are persisted in the session tree and survive
+// restarts.
+//
+// Commands:
+//
+//	/bookmark <label>  — bookmark the current point with a label
+//	/bookmarks         — list all bookmarks in this session
+//
+// Usage: kit -e examples/extensions/bookmark.go
+func Init(api ext.API) {
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "bookmark",
+		Description: "Bookmark the current point in the conversation",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			label := strings.TrimSpace(args)
+			if label == "" {
+				label = time.Now().Format("15:04:05")
+			}
+
+			// Count existing messages to record position.
+			msgs := ctx.GetMessages()
+
+			data, _ := json.Marshal(map[string]any{
+				"label":    label,
+				"messages": len(msgs),
+			})
+
+			_, err := ctx.AppendEntry("bookmark", string(data))
+			if err != nil {
+				ctx.PrintError("Failed to save bookmark: " + err.Error())
+				return "", nil
+			}
+
+			ctx.PrintInfo(fmt.Sprintf("Bookmarked: %s (at message %d)", label, len(msgs)))
+			return "", nil
+		},
+		Complete: func(prefix string, ctx ext.Context) []string {
+			// Suggest existing bookmark labels so the user can quickly
+			// re-bookmark at the same label.
+			entries := ctx.GetEntries("bookmark")
+			var labels []string
+			seen := map[string]bool{}
+			for _, e := range entries {
+				var data map[string]any
+				if err := json.Unmarshal([]byte(e.Data), &data); err != nil {
+					continue
+				}
+				label, _ := data["label"].(string)
+				if label == "" || seen[label] {
+					continue
+				}
+				if prefix == "" || strings.HasPrefix(strings.ToLower(label), strings.ToLower(prefix)) {
+					labels = append(labels, label)
+					seen[label] = true
+				}
+			}
+			return labels
+		},
+	})
+
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "bookmarks",
+		Description: "List all bookmarks in this session",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			entries := ctx.GetEntries("bookmark")
+			if len(entries) == 0 {
+				ctx.PrintInfo("No bookmarks yet. Use /bookmark <label> to create one.")
+				return "", nil
+			}
+
+			var lines []string
+			for i, e := range entries {
+				var data map[string]any
+				if err := json.Unmarshal([]byte(e.Data), &data); err != nil {
+					continue
+				}
+				label, _ := data["label"].(string)
+				msgCount, _ := data["messages"].(float64)
+				lines = append(lines, fmt.Sprintf("  %d. %s (msg %d, %s)",
+					i+1, label, int(msgCount), e.Timestamp[:19]))
+			}
+
+			ctx.PrintInfo("Bookmarks:\n" + strings.Join(lines, "\n"))
+			return "", nil
+		},
+	})
+}

examples/extensions/branded-output.go

@@ -0,0 +1,76 @@
+//go:build ignore
+
+// branded-output.go — Custom Message Rendering example extension for Kit.
+//
+// Demonstrates api.RegisterMessageRenderer() and ctx.RenderMessage() which
+// let extensions define reusable visual styles for output. Each renderer has
+// a name and a render function that receives content and terminal width.
+//
+// This extension registers three renderers:
+//   "success" — green-bordered block for success messages
+//   "warning" — yellow-bordered block for warnings
+//   "metric"  — compact key=value display for metrics
+//
+// Commands:
+//   /demo-render   — shows all three renderers in action
+
+package main
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	ext "kit/ext"
+)
+
+func Init(api ext.API) {
+	// Register a "success" renderer — green-accented block.
+	api.RegisterMessageRenderer(ext.MessageRendererConfig{
+		Name: "success",
+		Render: func(content string, width int) string {
+			maxW := width - 6
+			if maxW < 20 {
+				maxW = 20
+			}
+			bar := strings.Repeat("─", maxW)
+			return fmt.Sprintf("  \033[32m┌%s┐\033[0m\n  \033[32m│\033[0m \033[1;32m%s\033[0m\n  \033[32m└%s┘\033[0m",
+				bar, content, bar)
+		},
+	})
+
+	// Register a "warning" renderer — yellow-accented block.
+	api.RegisterMessageRenderer(ext.MessageRendererConfig{
+		Name: "warning",
+		Render: func(content string, width int) string {
+			maxW := width - 6
+			if maxW < 20 {
+				maxW = 20
+			}
+			bar := strings.Repeat("─", maxW)
+			return fmt.Sprintf("  \033[33m┌%s┐\033[0m\n  \033[33m│\033[0m \033[1;33m%s\033[0m\n  \033[33m└%s┘\033[0m",
+				bar, content, bar)
+		},
+	})
+
+	// Register a "metric" renderer — compact label: value format.
+	api.RegisterMessageRenderer(ext.MessageRendererConfig{
+		Name: "metric",
+		Render: func(content string, width int) string {
+			return fmt.Sprintf("  \033[36m▸\033[0m %s", content)
+		},
+	})
+
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "demo-render",
+		Description: "Demonstrate custom message renderers",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			ctx.RenderMessage("success", "All 42 tests passed in 3.2s")
+			ctx.RenderMessage("warning", "3 deprecation warnings detected")
+			ctx.RenderMessage("metric", fmt.Sprintf("build_time=%.1fs  tests=42  coverage=87%%  timestamp=%s",
+				3.2, time.Now().Format("15:04:05")))
+
+			return "Rendered three message styles.", nil
+		},
+	})
+}

examples/extensions/compact-notify.go

@@ -0,0 +1,56 @@
+//go:build ignore
+
+package main
+
+import (
+	"fmt"
+
+	"kit/ext"
+)
+
+// Init registers a before-compact hook that notifies the user when
+// compaction is about to happen and optionally blocks automatic compaction.
+//
+// When automatic compaction is triggered (via --auto-compact), the extension
+// asks for user confirmation. Manual /compact commands are always allowed.
+//
+// This demonstrates the OnBeforeCompact event which allows extensions to
+// inspect context usage stats and gate the compaction process.
+//
+// Usage: kit -e examples/extensions/compact-notify.go --auto-compact
+func Init(api ext.API) {
+	api.OnBeforeCompact(func(e ext.BeforeCompactEvent, ctx ext.Context) *ext.BeforeCompactResult {
+		pct := int(e.UsagePercent * 100)
+		summary := fmt.Sprintf("Context: %dk/%dk tokens (%d%%), %d messages",
+			e.EstimatedTokens/1000, e.ContextLimit/1000, pct, e.MessageCount)
+
+		if e.IsAutomatic {
+			// Auto-compaction: ask user first.
+			ctx.PrintBlock(ext.PrintBlockOpts{
+				Text:        "Auto-compaction triggered.\n" + summary,
+				BorderColor: "#f9e2af",
+				Subtitle:    "compact-notify",
+			})
+
+			result := ctx.PromptConfirm(ext.PromptConfirmConfig{
+				Message:      "Allow automatic compaction?",
+				DefaultValue: true,
+			})
+			if result.Cancelled || !result.Value {
+				return &ext.BeforeCompactResult{
+					Cancel: true,
+					Reason: "Auto-compaction skipped by user.",
+				}
+			}
+		} else {
+			// Manual /compact: just notify.
+			ctx.PrintBlock(ext.PrintBlockOpts{
+				Text:        "Compacting conversation...\n" + summary,
+				BorderColor: "#89b4fa",
+				Subtitle:    "compact-notify",
+			})
+		}
+
+		return nil // allow compaction
+	})
+}

examples/extensions/confirm-destructive.go

@@ -0,0 +1,72 @@
+//go:build ignore
+
+package main
+
+import (
+	"os/exec"
+	"strings"
+
+	"kit/ext"
+)
+
+// Init registers before-hooks for destructive session operations:
+//   - Forks: Asks for confirmation before branching to a different tree node.
+//   - New sessions: Checks for uncommitted git changes and warns before
+//     starting a new branch if the working tree is dirty.
+//
+// This demonstrates the OnBeforeFork and OnBeforeSessionSwitch events
+// which allow extensions to cancel session lifecycle operations.
+//
+// Usage: kit -e examples/extensions/confirm-destructive.go --continue
+func Init(api ext.API) {
+	// Gate /new command: warn if there are uncommitted git changes.
+	api.OnBeforeSessionSwitch(func(e ext.BeforeSessionSwitchEvent, ctx ext.Context) *ext.BeforeSessionSwitchResult {
+		if !isGitDirty() {
+			return nil // clean repo, allow switch
+		}
+
+		result := ctx.PromptConfirm(ext.PromptConfirmConfig{
+			Message: "Working tree has uncommitted changes. Start new session anyway?",
+		})
+		if result.Cancelled || !result.Value {
+			return &ext.BeforeSessionSwitchResult{
+				Cancel: true,
+				Reason: "Session switch cancelled: uncommitted git changes.",
+			}
+		}
+		return nil // user approved
+	})
+
+	// Gate fork: ask for confirmation before branching.
+	api.OnBeforeFork(func(e ext.BeforeForkEvent, ctx ext.Context) *ext.BeforeForkResult {
+		msg := "Branch to this point in the conversation?"
+		if e.IsUserMessage && e.UserText != "" {
+			// Show a preview of the user message being forked to.
+			preview := e.UserText
+			if len(preview) > 80 {
+				preview = preview[:77] + "..."
+			}
+			msg = "Fork and edit: " + preview + "\n\nContinue?"
+		}
+
+		result := ctx.PromptConfirm(ext.PromptConfirmConfig{
+			Message: msg,
+		})
+		if result.Cancelled || !result.Value {
+			return &ext.BeforeForkResult{
+				Cancel: true,
+				Reason: "Fork cancelled by user.",
+			}
+		}
+		return nil // user approved
+	})
+}
+
+// isGitDirty returns true if the git working tree has uncommitted changes.
+func isGitDirty() bool {
+	out, err := exec.Command("git", "status", "--porcelain").Output()
+	if err != nil {
+		return false // not a git repo or git not available
+	}
+	return len(strings.TrimSpace(string(out))) > 0
+}

examples/extensions/context-inject.go

@@ -0,0 +1,89 @@
+//go:build ignore
+
+// context-inject.go — Injects context from a local file into every LLM turn.
+//
+// Reads a context file (default: .kit/context.md) and prepends it as a system
+// message to every LLM context window via OnContextPrepare. This is useful for
+// injecting project-specific knowledge, coding standards, or RAG results that
+// should always be visible to the model — without cluttering the session history.
+//
+// The injected message does NOT persist in the session tree (it's ephemeral,
+// added at query time only). This means:
+//   - Changing the context file immediately affects future turns
+//   - No session bloat from repeated context injection
+//   - The model always sees the latest version of the context
+//
+// Configuration:
+//
+//	KIT_OPT_CONTEXT_FILE  — path to context file (default: .kit/context.md)
+//
+// Usage:
+//
+//	kit -e examples/extensions/context-inject.go
+//	echo "Always use error wrapping with fmt.Errorf" > .kit/context.md
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	ext "kit/ext"
+)
+
+func Init(api ext.API) {
+	api.RegisterOption(ext.OptionDef{
+		Name:        "context-file",
+		Description: "Path to the context file to inject into every turn",
+		Default:     ".kit/context.md",
+	})
+
+	api.OnContextPrepare(func(e ext.ContextPrepareEvent, ctx ext.Context) *ext.ContextPrepareResult {
+		path := ctx.GetOption("context-file")
+		if path == "" {
+			return nil
+		}
+
+		data, err := os.ReadFile(path)
+		if err != nil {
+			// File doesn't exist or can't be read — skip silently.
+			return nil
+		}
+
+		content := strings.TrimSpace(string(data))
+		if content == "" {
+			return nil
+		}
+
+		// Prepend a system message with the context file contents.
+		injected := ext.ContextMessage{
+			Index:   -1,
+			Role:    "system",
+			Content: fmt.Sprintf("[Project Context from %s]\n\n%s", path, content),
+		}
+
+		msgs := make([]ext.ContextMessage, 0, len(e.Messages)+1)
+		msgs = append(msgs, injected)
+		msgs = append(msgs, e.Messages...)
+
+		return &ext.ContextPrepareResult{Messages: msgs}
+	})
+
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "context",
+		Description: "Show or edit the injected context file path",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			path := ctx.GetOption("context-file")
+			data, err := os.ReadFile(path)
+			if err != nil {
+				return fmt.Sprintf("Context file: %s (not found or unreadable)", path), nil
+			}
+			lines := strings.Split(strings.TrimSpace(string(data)), "\n")
+			preview := strings.Join(lines, "\n")
+			if len(lines) > 10 {
+				preview = strings.Join(lines[:10], "\n") + "\n..."
+			}
+			return fmt.Sprintf("Context file: %s (%d lines)\n\n%s", path, len(lines), preview), nil
+		},
+	})
+}

examples/extensions/dev-reload.go

@@ -0,0 +1,56 @@
+//go:build ignore
+
+// dev-reload.go — Extension Hot-Reload example extension for Kit.
+//
+// Demonstrates ctx.ReloadExtensions() which hot-reloads all extensions
+// from disk without restarting Kit. This is invaluable during extension
+// development: edit your extension source, then type /reload to pick up
+// changes immediately.
+//
+// Event handlers, slash commands, tool renderers, message renderers, and
+// keyboard shortcuts update immediately. Extension-defined tools are NOT
+// updated (they are baked into the agent at creation time and require a
+// restart).
+//
+// Commands:
+//   /reload   — hot-reload all extensions from disk
+
+package main
+
+import (
+	"fmt"
+	"time"
+
+	ext "kit/ext"
+)
+
+var loadedAt string
+
+func Init(api ext.API) {
+	loadedAt = time.Now().Format("15:04:05")
+
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "reload",
+		Description: "Hot-reload all extensions from disk",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			ctx.Print("Reloading extensions...")
+			err := ctx.ReloadExtensions()
+			if err != nil {
+				return "", fmt.Errorf("reload failed: %w", err)
+			}
+			return "Extensions reloaded successfully.", nil
+		},
+	})
+
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "load-time",
+		Description: "Show when this extension was loaded",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			return fmt.Sprintf("This extension was loaded at %s", loadedAt), nil
+		},
+	})
+
+	api.OnSessionStart(func(e ext.SessionStartEvent, ctx ext.Context) {
+		ctx.Print(fmt.Sprintf("[dev-reload] Extension loaded at %s", loadedAt))
+	})
+}

examples/extensions/extension_test_template.go

@@ -0,0 +1,170 @@
+// Extension Test Template
+//
+// This is a template for writing tests for your Kit extension.
+// Copy this file to your extension directory, rename it to something like
+// "my-ext_test.go", and customize it for your extension.
+//
+// Run tests with: go test -v
+//
+// IMPORTANT: This file should be in the same directory as your extension
+// and use package main, NOT package test.
+
+package main
+
+import (
+	"testing"
+
+	"github.com/mark3labs/kit/internal/extensions"
+	"github.com/mark3labs/kit/pkg/extensions/test"
+)
+
+// Test that your extension loads without errors
+func TestExtension_Loads(t *testing.T) {
+	harness := test.New(t)
+	ext := harness.LoadFile("my-ext.go") // Change to your extension filename
+
+	// Verify the extension was loaded
+	if ext == nil {
+		t.Fatal("extension should not be nil")
+	}
+}
+
+// Test your event handlers are registered
+func TestExtension_EventHandlers(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("my-ext.go")
+
+	// Uncomment the handlers your extension uses:
+	// test.AssertHasHandlers(t, harness, extensions.ToolCall)
+	// test.AssertHasHandlers(t, harness, extensions.Input)
+	// test.AssertHasHandlers(t, harness, extensions.SessionStart)
+	// test.AssertHasHandlers(t, harness, extensions.AgentEnd)
+}
+
+// Test tool registration
+func TestExtension_Tools(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("my-ext.go")
+
+	// Test that your tools are registered
+	// test.AssertToolRegistered(t, harness, "my_tool")
+
+	// Or test all registered tools
+	tools := harness.RegisteredTools()
+	t.Logf("Registered %d tools", len(tools))
+	for _, tool := range tools {
+		t.Logf("  - %s: %s", tool.Name, tool.Description)
+	}
+}
+
+// Test command registration
+func TestExtension_Commands(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("my-ext.go")
+
+	// Test that your commands are registered
+	// test.AssertCommandRegistered(t, harness, "mycommand")
+
+	// Or test all registered commands
+	cmds := harness.RegisteredCommands()
+	t.Logf("Registered %d commands", len(cmds))
+	for _, cmd := range cmds {
+		t.Logf("  - %s: %s", cmd.Name, cmd.Description)
+	}
+}
+
+// Test session start behavior
+func TestExtension_SessionStart(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("my-ext.go")
+
+	// Emit session start event
+	_, err := harness.Emit(extensions.SessionStartEvent{
+		SessionID: "test-session",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Verify expected behavior:
+	// - Did it print something?
+	// test.AssertPrinted(t, harness, "expected output")
+
+	// - Did it set a widget?
+	// test.AssertWidgetSet(t, harness, "my-widget")
+	// test.AssertWidgetText(t, harness, "my-widget", "expected text")
+
+	// - Did it set the header/footer?
+	// test.AssertHeaderSet(t, harness)
+	// test.AssertFooterSet(t, harness)
+
+	// - Did it set a status?
+	// test.AssertStatusSet(t, harness, "myext:status")
+}
+
+// Test tool call handling
+func TestExtension_ToolCall(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("my-ext.go")
+
+	// Test a specific tool call
+	result, err := harness.Emit(extensions.ToolCallEvent{
+		ToolName: "some_tool",
+		Input:    `{"key": "value"}`,
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// If your extension blocks certain tools:
+	// test.AssertNotBlocked(t, result)
+	// OR
+	// test.AssertBlocked(t, result, "expected reason")
+
+	// Suppress unused variable warning (remove this when using result)
+	_ = result
+
+	// Check for print output
+	// test.AssertPrinted(t, harness, "expected message")
+}
+
+// Test input handling
+func TestExtension_InputHandling(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("my-ext.go")
+
+	// Test input that should be handled
+	result, err := harness.Emit(extensions.InputEvent{
+		Text:   "test input",
+		Source: "cli",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// If your extension handles/transforms input:
+	// test.AssertInputHandled(t, result, "handled")
+	// OR
+	// test.AssertInputTransformed(t, result, "transformed text")
+
+	// Suppress unused variable warning (remove this when using result)
+	_ = result
+}
+
+// Test with configured prompt results
+func TestExtension_WithPrompts(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("my-ext.go")
+
+	// Configure what prompts should return
+	harness.Context().SetPromptSelectResult(extensions.PromptSelectResult{
+		Value:     "option1",
+		Index:     0,
+		Cancelled: false,
+	})
+
+	// Now when your extension calls ctx.PromptSelect(), it gets the configured result
+	_, _ = harness.Emit(extensions.SessionStartEvent{SessionID: "test"})
+
+	// Verify behavior based on the selected options
+}

examples/extensions/inline-bash.go

@@ -0,0 +1,52 @@
+//go:build ignore
+
+package main
+
+import (
+	"os/exec"
+	"regexp"
+	"strings"
+
+	"kit/ext"
+)
+
+// Init expands inline bash expressions in user prompts before they reach the
+// LLM. Text like !{git branch --show-current} is replaced with the command's
+// stdout.
+//
+// Examples:
+//
+//	"Fix the tests on !{git branch --show-current}"
+//	  → "Fix the tests on main"
+//
+//	"The current directory is !{pwd}"
+//	  → "The current directory is /home/user/project"
+//
+// Usage: kit -e examples/extensions/inline-bash.go
+func Init(api ext.API) {
+	// Matches !{...} with non-greedy content.
+	re := regexp.MustCompile(`!\{([^}]+)\}`)
+
+	api.OnInput(func(ev ext.InputEvent, ctx ext.Context) *ext.InputResult {
+		if !re.MatchString(ev.Text) {
+			return nil
+		}
+
+		expanded := re.ReplaceAllStringFunc(ev.Text, func(match string) string {
+			// Extract the command between !{ and }.
+			cmd := re.FindStringSubmatch(match)[1]
+			cmd = strings.TrimSpace(cmd)
+
+			out, err := exec.Command("bash", "-c", cmd).Output()
+			if err != nil {
+				return match // keep original on error
+			}
+			return strings.TrimSpace(string(out))
+		})
+
+		return &ext.InputResult{
+			Action: "transform",
+			Text:   expanded,
+		}
+	})
+}

examples/extensions/interactive-shell.go

@@ -0,0 +1,123 @@
+//go:build ignore
+
+// interactive-shell.go — TUI Suspend example extension for Kit.
+//
+// Demonstrates ctx.SuspendTUI() which temporarily releases the terminal
+// from the TUI so interactive subprocesses can run with full terminal
+// control. The TUI is automatically restored when the callback returns.
+//
+// Commands:
+//   /edit <file>   — opens $EDITOR (or vi) to edit a file
+//   /shell         — drops into an interactive shell session
+//   /run <cmd>     — runs a command with full terminal I/O (no TUI capture)
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+
+	ext "kit/ext"
+)
+
+func Init(api ext.API) {
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "edit",
+		Description: "Open $EDITOR to edit a file (TUI suspends)",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			file := strings.TrimSpace(args)
+			if file == "" {
+				return "", fmt.Errorf("usage: /edit <file>")
+			}
+
+			editor := os.Getenv("EDITOR")
+			if editor == "" {
+				editor = "vi"
+			}
+
+			ctx.Print(fmt.Sprintf("Opening %s in %s...", file, editor))
+
+			err := ctx.SuspendTUI(func() {
+				cmd := exec.Command(editor, file)
+				cmd.Stdin = os.Stdin
+				cmd.Stdout = os.Stdout
+				cmd.Stderr = os.Stderr
+				cmd.Run()
+			})
+			if err != nil {
+				return "", fmt.Errorf("editor session failed: %w", err)
+			}
+
+			return fmt.Sprintf("Finished editing %s", file), nil
+		},
+		Complete: func(prefix string, ctx ext.Context) []string {
+			// Suggest files in the current directory.
+			entries, err := os.ReadDir(".")
+			if err != nil {
+				return nil
+			}
+			var results []string
+			for _, e := range entries {
+				name := e.Name()
+				if strings.HasPrefix(name, prefix) {
+					results = append(results, name)
+				}
+			}
+			return results
+		},
+	})
+
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "shell",
+		Description: "Drop into an interactive shell (TUI suspends)",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			shell := os.Getenv("SHELL")
+			if shell == "" {
+				shell = "/bin/sh"
+			}
+
+			ctx.Print(fmt.Sprintf("Starting %s... (type 'exit' to return to Kit)", shell))
+
+			err := ctx.SuspendTUI(func() {
+				cmd := exec.Command(shell)
+				cmd.Stdin = os.Stdin
+				cmd.Stdout = os.Stdout
+				cmd.Stderr = os.Stderr
+				cmd.Run()
+			})
+			if err != nil {
+				return "", fmt.Errorf("shell session failed: %w", err)
+			}
+
+			return "Shell session ended, TUI restored.", nil
+		},
+	})
+
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "run",
+		Description: "Run a command with full terminal I/O (TUI suspends)",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			cmdStr := strings.TrimSpace(args)
+			if cmdStr == "" {
+				return "", fmt.Errorf("usage: /run <command>")
+			}
+
+			ctx.Print(fmt.Sprintf("Running: %s", cmdStr))
+
+			err := ctx.SuspendTUI(func() {
+				cmd := exec.Command("sh", "-c", cmdStr)
+				cmd.Stdin = os.Stdin
+				cmd.Stdout = os.Stdout
+				cmd.Stderr = os.Stderr
+				cmd.Run()
+			})
+			if err != nil {
+				return "", fmt.Errorf("command failed: %w", err)
+			}
+
+			return "Command finished, TUI restored.", nil
+		},
+	})
+}

examples/extensions/kit-kit.go

@@ -19,6 +19,7 @@
 package main
 
 import (
+	"bytes"
 	"encoding/json"
 	"fmt"
 	"os"
@@ -31,6 +32,16 @@ import (
 	"kit/ext"
 )
 
+// kitJSONOutput matches the JSON envelope produced by `kit --json`.
+type kitJSONOutput struct {
+	Response string `json:"response"`
+	Model    string `json:"model"`
+	Usage    *struct {
+		InputTokens  int64 `json:"input_tokens"`
+		OutputTokens int64 `json:"output_tokens"`
+	} `json:"usage,omitempty"`
+}
+
 // ---------------------------------------------------------------------------
 // Types
 // ---------------------------------------------------------------------------
@@ -474,27 +485,33 @@ func queryExpert(name, question string) (output string, exitCode int, elapsed ti
 	}
 	tmpFile.Close()
 
-	// Build subprocess arguments. Don't pass --model; the subprocess
-	// inherits the same config/env and will use the same default.
+	// Build subprocess arguments. Use --json for structured output parsing.
+	// Don't pass --model; the subprocess inherits the same config/env default.
 	args := []string{
-		"--prompt", question,
-		"--quiet",
+		"--json",
 		"--no-session",
 		"--no-extensions",
 		"--system-prompt", tmpFile.Name(),
+		question,
 	}
 
+	var stdoutBuf, stderrBuf bytes.Buffer
 	cmd := exec.Command(kitBinary, args...)
 	cmd.Env = os.Environ()
+	cmd.Stdout = &stdoutBuf
+	cmd.Stderr = &stderrBuf
 
-	outBytes, err := cmd.CombinedOutput()
+	err = cmd.Run()
 	close(done)
 	elapsed = time.Since(start)
-	result := strings.TrimSpace(string(outBytes))
 
 	if err != nil {
-		// Extract a single-line summary for the card (no newlines).
-		errLine := result
+		// On error, prefer stderr for the error message; fall back to stdout.
+		errText := strings.TrimSpace(stderrBuf.String())
+		if errText == "" {
+			errText = strings.TrimSpace(stdoutBuf.String())
+		}
+		errLine := errText
 		if idx := strings.Index(errLine, "\n"); idx >= 0 {
 			errLine = errLine[:idx]
 		}
@@ -505,10 +522,18 @@ func queryExpert(name, question string) (output string, exitCode int, elapsed ti
 		if exitErr, ok := err.(*exec.ExitError); ok {
 			code = exitErr.ExitCode()
 		}
-		return result, code, elapsed
+		return errText, code, elapsed
 	}
 
-	// Success — extract last non-empty line for the card.
+	// Parse JSON output from subprocess.
+	var parsed kitJSONOutput
+	result := strings.TrimSpace(stdoutBuf.String())
+	if err := json.Unmarshal([]byte(result), &parsed); err == nil {
+		result = parsed.Response
+	}
+	// else: fall back to raw stdout (e.g. older kit binary without --json)
+
+	// Extract last non-empty line for the card.
 	lines := strings.Split(result, "\n")
 	var lastLine string
 	for i := len(lines) - 1; i >= 0; i-- {

examples/extensions/kit-telegram/README.md

@@ -0,0 +1,111 @@
+# kit-telegram
+
+A Kit extension that relays all Kit agent runs to Telegram and lets approved Telegram users reply back into Kit.
+
+## What it does
+
+- Relays **all Kit runs** to one Telegram chat while connected
+- Edits one Telegram progress message in place during a run
+- Lets approved Telegram users send normal text replies back into Kit
+- Shows `Telegram Connected` or `Telegram Disconnected` in the status bar
+- Shows a small spinner animation as `⠋ Telegram Connecting` only while the relay is still connecting
+- On startup with an already validated enabled config, sends a short Telegram connection message to confirm the relay is up
+
+## Requirements
+
+- `kit` installed and working
+- A Telegram bot token from `@BotFather`
+- Either:
+  - A Telegram chat where you can message the bot, or
+  - A numeric Telegram chat id you want to enter manually
+- For group chats, one or more allowed Telegram user ids
+
+## Quickstart
+
+### 1. Install the extension
+
+```bash
+kit install github.com/mark3labs/kit/examples/extensions/kit-telegram
+```
+
+Or run directly:
+```bash
+kit -e path/to/kit-telegram/main.go
+```
+
+### 2. Start Kit and connect Telegram
+
+```bash
+kit
+```
+
+Inside Kit, run:
+
+```
+/telegram connect
+```
+
+You will be prompted for:
+
+- Bot token from `@BotFather`
+- Whether to auto-detect the chat by messaging the bot or enter the chat id manually
+- Allowed user ids when needed
+
+### 3. Verify the relay
+
+```
+/telegram test
+```
+
+Reply in Telegram with the code from the test message.
+
+## Commands
+
+| Command | Description |
+|---------|-------------|
+| `/telegram` | Human-friendly overview and subcommand list |
+| `/telegram status` | Raw deterministic relay state |
+| `/telegram test` | Verify outbound and inbound relay |
+| `/telegram toggle` | Enable or disable relay without deleting credentials |
+| `/telegram logout` | Remove saved credentials and disconnect relay |
+| `/telegram connect` | Run the setup flow again |
+| `/telegram clear` | Clear Telegram status and working messages from the TUI |
+
+## Remote commands (from Telegram)
+
+| Command | Description |
+|---------|-------------|
+| `/telegram` | Sends the overview back to Telegram |
+| `/telegram status` | Sends the deterministic state report to Telegram |
+| `/telegram test` | Sends a reply-code test message from Telegram |
+| `/telegram toggle` | Flips the enabled flag |
+| `/telegram logout yes` | Logs out (requires `yes` confirmation) |
+| `/telegram clear` | Clears the TUI footer and working messages |
+
+## Key APIs Used
+
+- `RegisterCommand` — Slash command with subcommands and tab completion
+- `OnSessionStart` / `OnSessionShutdown` — Lifecycle management
+- `OnAgentStart` / `OnAgentEnd` — Run tracking and progress rendering
+- `OnToolCall` / `OnToolResult` — Action tracking
+- `OnMessageEnd` — Capture assistant responses
+- `OnInput` — Mirror local messages to Telegram
+- `SetStatus` / `RemoveStatus` — Status bar indicators
+- `SetWidget` / `RemoveWidget` — Working message display
+- `PromptInput` / `PromptSelect` / `PromptConfirm` — Interactive setup flow
+- `SendMessage` — Inject Telegram replies as Kit prompts
+
+## Architecture
+
+Single Go file interpreted by Yaegi at runtime. Core components:
+
+- **Telegram Bot API client** — HTTP calls via `net/http` for getMe, getChat, getChatMember, getUpdates (long-polling), sendMessage, editMessageText
+- **Config persistence** — JSON file at `.kit/kit-telegram.json` with atomic writes
+- **Long-polling goroutine** — Background polling for Telegram updates with warmup poll, retry, and client-side timeouts
+- **Message queue** — In-memory FIFO queue for Telegram prompt input with edit-before-dispatch support
+- **Progress rendering** — `⏳ elapsed · step N` with action lines, edited in place
+- **Final rendering** — `✅/❌ elapsed` with response text, split into chunks for long output
+
+## Debug mode
+
+Set environment variable `KIT_TELEGRAM_DEBUG=1` to enable verbose debug logging.

examples/extensions/minimal.go

@@ -0,0 +1,71 @@
+//go:build ignore
+
+package main
+
+import (
+	"fmt"
+	"math"
+	"strings"
+
+	"kit/ext"
+)
+
+// Init demonstrates a minimal-chrome extension.
+// Hides the startup banner, status bar, separator, and input hint, replacing
+// them with a compact footer showing model name and a context usage bar:
+//
+//	claude-sonnet-4-5-20250929  [###-------] 30%  (3.9K/200K tokens)
+//
+// Usage: kit -e examples/extensions/minimal.go
+func Init(api ext.API) {
+	// updateFooter builds the footer text from current context stats.
+	updateFooter := func(ctx ext.Context) {
+		stats := ctx.GetContextStats()
+		pct := stats.UsagePercent * 100
+		if pct > 100 {
+			pct = 100
+		}
+		filled := int(math.Round(pct)) / 10
+		bar := strings.Repeat("#", filled) + strings.Repeat("-", 10-filled)
+
+		// Format token counts like the built-in status bar (e.g. "3.9K/200K").
+		fmtTokens := func(n int) string {
+			if n >= 1000 {
+				return fmt.Sprintf("%.1fK", float64(n)/1000)
+			}
+			return fmt.Sprintf("%d", n)
+		}
+
+		text := fmt.Sprintf("%s  [%s] %d%%", ctx.Model, bar, int(math.Round(pct)))
+		if stats.ContextLimit > 0 {
+			text += fmt.Sprintf("  (%s/%s tokens)",
+				fmtTokens(stats.EstimatedTokens), fmtTokens(stats.ContextLimit))
+		}
+
+		ctx.SetFooter(ext.HeaderFooterConfig{
+			Content: ext.WidgetContent{Text: text},
+			Style:   ext.WidgetStyle{BorderColor: "#585b70"},
+		})
+	}
+
+	api.OnSessionStart(func(_ ext.SessionStartEvent, ctx ext.Context) {
+		// Strip built-in chrome for a minimal look.
+		ctx.SetUIVisibility(ext.UIVisibility{
+			HideStartupMessage: true,
+			HideStatusBar:      true,
+			HideSeparator:      true,
+			HideInputHint:      true,
+		})
+
+		updateFooter(ctx)
+	})
+
+	// Refresh after each agent turn — context usage changes here.
+	api.OnAgentEnd(func(_ ext.AgentEndEvent, ctx ext.Context) {
+		updateFooter(ctx)
+	})
+
+	api.OnSessionShutdown(func(_ ext.SessionShutdownEvent, ctx ext.Context) {
+		ctx.RemoveFooter()
+	})
+}

examples/extensions/neon-theme.go

@@ -0,0 +1,42 @@
+//go:build ignore
+
+package main
+
+import "kit/ext"
+
+// Init registers a "neon" theme and a /neon slash command to apply it.
+// Demonstrates how extensions can create and set themes programmatically.
+//
+// Usage: kit -e examples/extensions/neon-theme.go
+func Init(api ext.API) {
+	api.OnSessionStart(func(_ ext.SessionStartEvent, ctx ext.Context) {
+		// Register a cyberpunk neon theme at startup.
+		ctx.RegisterTheme("neon", ext.ThemeColorConfig{
+			Primary:    ext.ThemeColor{Light: "#CC00FF", Dark: "#FF00FF"},
+			Secondary:  ext.ThemeColor{Light: "#0088CC", Dark: "#00FFFF"},
+			Success:    ext.ThemeColor{Light: "#00CC44", Dark: "#00FF66"},
+			Warning:    ext.ThemeColor{Light: "#CCAA00", Dark: "#FFFF00"},
+			Error:      ext.ThemeColor{Light: "#CC0033", Dark: "#FF0055"},
+			Info:       ext.ThemeColor{Light: "#0088CC", Dark: "#00CCFF"},
+			Text:       ext.ThemeColor{Light: "#111111", Dark: "#F0F0F0"},
+			Background: ext.ThemeColor{Light: "#F0F0F0", Dark: "#0A0A14"},
+			MdKeyword:  ext.ThemeColor{Light: "#CC00FF", Dark: "#FF00FF"},
+			MdString:   ext.ThemeColor{Light: "#00CC44", Dark: "#00FF66"},
+			MdComment:  ext.ThemeColor{Light: "#888888", Dark: "#555555"},
+		})
+
+		ctx.PrintInfo("Neon theme registered! Use /theme neon to activate.")
+	})
+
+	// Also register a /neon slash command as a shortcut.
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "neon",
+		Description: "Switch to the neon cyberpunk theme",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			if err := ctx.SetTheme("neon"); err != nil {
+				return "", err
+			}
+			return "Neon theme activated!", nil
+		},
+	})
+}

examples/extensions/notify.go

@@ -0,0 +1,34 @@
+//go:build ignore
+
+package main
+
+import (
+	"os/exec"
+	"runtime"
+
+	"kit/ext"
+)
+
+// Init sends a desktop notification when the agent finishes responding.
+// Useful for long-running tasks — get notified without watching the terminal.
+
+// Supports: Linux (notify-send), macOS (osascript).
+//
+// Usage: kit -e examples/extensions/notify.go
+func Init(api ext.API) {
+	api.OnAgentEnd(func(_ ext.AgentEndEvent, ctx ext.Context) {
+		sendNotification("Kit", "Agent finished responding")
+	})
+}
+
+func sendNotification(title, body string) {
+	switch runtime.GOOS {
+	case "linux":
+		// Uses notify-send (libnotify) — available on most Linux desktops.
+		_ = exec.Command("notify-send", "-a", "Kit", title, body).Start()
+	case "darwin":
+		// Uses macOS built-in osascript for native notifications.
+		script := `display notification "` + body + `" with title "` + title + `"`
+		_ = exec.Command("osascript", "-e", script).Start()
+	}
+}

examples/extensions/permission-gate.go

@@ -0,0 +1,64 @@
+//go:build ignore
+
+package main
+
+import (
+	"encoding/json"
+	"strings"
+
+	"kit/ext"
+)
+
+// Init intercepts potentially dangerous bash commands and asks the user for
+// confirmation before allowing execution.
+//
+// Dangerous patterns: rm -rf, sudo, chmod 777, mkfs, dd, > /dev/
+//
+// Usage: kit -e examples/extensions/permission-gate.go
+func Init(api ext.API) {
+	// Patterns that require user confirmation.
+	dangerousPatterns := []string{
+		"rm -rf",
+		"rm -r /",
+		"sudo ",
+		"chmod 777",
+		"chmod -R 777",
+		"mkfs",
+		"dd if=",
+		"> /dev/",
+		":(){ :|:& };:",
+	}
+
+	api.OnToolCall(func(tc ext.ToolCallEvent, ctx ext.Context) *ext.ToolCallResult {
+		if tc.ToolName != "Bash" {
+			return nil
+		}
+
+		// Extract the command from the tool input JSON.
+		var input struct {
+			Command string `json:"command"`
+		}
+		if err := json.Unmarshal([]byte(tc.Input), &input); err != nil {
+			return nil
+		}
+		cmd := strings.ToLower(input.Command)
+
+		// Check for dangerous patterns.
+		for _, pattern := range dangerousPatterns {
+			if strings.Contains(cmd, strings.ToLower(pattern)) {
+				result := ctx.PromptConfirm(ext.PromptConfirmConfig{
+					Message: "Dangerous command detected: " + input.Command + "\n\nAllow execution?",
+				})
+				if result.Cancelled || !result.Value {
+					return &ext.ToolCallResult{
+						Block:  true,
+						Reason: "User denied execution of dangerous command: " + input.Command,
+					}
+				}
+				return nil // user approved
+			}
+		}
+
+		return nil
+	})
+}

examples/extensions/pirate.go

@@ -0,0 +1,28 @@
+//go:build ignore
+
+package main
+
+import "kit/ext"
+
+// Init injects a pirate persona into the system prompt, causing the LLM to
+// respond in pirate-speak. Demonstrates OnBeforeAgentStart system prompt
+// injection.
+//
+// Usage: kit -e examples/extensions/pirate.go
+func Init(api ext.API) {
+	piratePrompt := `
+You are a pirate! You must:
+- Start every response with "Ahoy!"
+- Use pirate slang (ye, matey, arr, landlubber, etc.)
+- Refer to files as "scrolls" and directories as "treasure chests"
+- Call errors "cursed mishaps" and bugs "sea monsters"
+- End responses with a pirate saying
+
+Despite the pirate persona, your technical advice must remain accurate and helpful.`
+
+	api.OnBeforeAgentStart(func(_ ext.BeforeAgentStartEvent, ctx ext.Context) *ext.BeforeAgentStartResult {
+		return &ext.BeforeAgentStartResult{
+			SystemPrompt: &piratePrompt,
+		}
+	})
+}

examples/extensions/plan-mode.go

@@ -0,0 +1,96 @@
+//go:build ignore
+
+package main
+
+import (
+	"strings"
+
+	"kit/ext"
+)
+
+// Init implements a plan/explore mode that restricts the agent to read-only
+// tools. Toggle with /plan (or start in plan mode via KIT_OPT_PLAN=true).
+
+// In plan mode the agent can only use read, grep, find, and ls — it cannot
+// write files, run bash, or make edits. This is useful for exploring a
+// codebase, reviewing architecture, or generating plans before executing.
+//
+// The status bar shows the current mode and the system prompt is augmented
+// with planning instructions when active.
+//
+// Usage: kit -e examples/extensions/plan-mode.go
+//
+// Start in plan mode: KIT_OPT_PLAN=true kit -e examples/extensions/plan-mode.go
+func Init(api ext.API) {
+	// Read-only tool set (matches core.ReadOnlyTools).
+	readOnlyTools := []string{"read", "grep", "find", "ls"}
+
+	var planActive bool
+
+	// Register "plan" option so users can start in plan mode via env/config.
+	api.RegisterOption(ext.OptionDef{
+		Name:        "plan",
+		Description: "Start in plan mode (read-only tools)",
+		Default:     "false",
+	})
+
+	// ctrl+alt+p — global shortcut to toggle plan mode.
+	api.RegisterShortcut(ext.ShortcutDef{
+		Key:         "ctrl+alt+p",
+		Description: "Toggle plan/explore mode",
+	}, func(ctx ext.Context) {
+		planActive = !planActive
+		applyMode(ctx, planActive, readOnlyTools)
+	})
+
+	// /plan — toggle plan mode on or off.
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "plan",
+		Description: "Toggle plan/explore mode (ctrl+alt+p)",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			planActive = !planActive
+			applyMode(ctx, planActive, readOnlyTools)
+			return "", nil
+		},
+	})
+
+	// Check option at session start to enable plan mode from env/config.
+	api.OnSessionStart(func(_ ext.SessionStartEvent, ctx ext.Context) {
+		opt := strings.ToLower(ctx.GetOption("plan"))
+		if opt == "true" || opt == "1" || opt == "yes" {
+			planActive = true
+			applyMode(ctx, true, readOnlyTools)
+		}
+	})
+
+	// Inject planning instructions into the system prompt when active.
+	api.OnBeforeAgentStart(func(_ ext.BeforeAgentStartEvent, ctx ext.Context) *ext.BeforeAgentStartResult {
+		if !planActive {
+			return nil
+		}
+		prompt := `You are in PLAN MODE (read-only exploration).
+You can ONLY read, search, and explore the codebase. You CANNOT write files,
+run commands, or make edits. Focus on:
+- Understanding the codebase structure and architecture
+- Identifying relevant files and patterns
+- Generating detailed plans and recommendations
+- Answering questions about how the code works
+
+When the user is ready to execute, they will exit plan mode with /plan.`
+		return &ext.BeforeAgentStartResult{
+			SystemPrompt: &prompt,
+		}
+	})
+}
+
+func applyMode(ctx ext.Context, active bool, readOnlyTools []string) {
+	if active {
+		ctx.SetActiveTools(readOnlyTools)
+		ctx.SetStatus("plan-mode", "PLAN MODE (read-only)", 10)
+		ctx.PrintInfo("Plan mode ON — agent restricted to read-only tools (read, grep, find, ls).\nUse /plan to toggle off.")
+	} else {
+		ctx.SetActiveTools(nil) // re-enable all tools
+		ctx.RemoveStatus("plan-mode")
+		ctx.PrintInfo("Plan mode OFF — all tools re-enabled.")
+	}
+}

examples/extensions/project-rules.go

@@ -0,0 +1,71 @@
+//go:build ignore
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"kit/ext"
+)
+
+// Init loads project-specific rules from .kit/rules/ into the system prompt.
+// Each .md file in the rules directory is injected as additional context,
+// giving projects a way to customise LLM behaviour without editing the
+// main system prompt.
+//
+// Place rule files in:
+//
+//	.kit/rules/code-style.md
+//	.kit/rules/testing.md
+//	.kit/rules/security.md
+//
+// Usage: kit -e examples/extensions/project-rules.go
+func Init(api ext.API) {
+	var rules string
+
+	api.OnSessionStart(func(_ ext.SessionStartEvent, ctx ext.Context) {
+		rulesDir := filepath.Join(ctx.CWD, ".kit", "rules")
+		entries, err := os.ReadDir(rulesDir)
+		if err != nil {
+			return // no rules directory, nothing to do
+		}
+
+		var parts []string
+		for _, entry := range entries {
+			if entry.IsDir() {
+				continue
+			}
+			name := entry.Name()
+			if !strings.HasSuffix(name, ".md") && !strings.HasSuffix(name, ".txt") {
+				continue
+			}
+			data, err := os.ReadFile(filepath.Join(rulesDir, name))
+			if err != nil {
+				continue
+			}
+			content := strings.TrimSpace(string(data))
+			if content != "" {
+				parts = append(parts, "## "+strings.TrimSuffix(name, filepath.Ext(name))+"\n\n"+content)
+			}
+		}
+
+		if len(parts) == 0 {
+			return
+		}
+
+		rules = "# Project Rules\n\n" + strings.Join(parts, "\n\n---\n\n")
+		ctx.PrintInfo(fmt.Sprintf("[project-rules] Loaded %d rule file(s) from .kit/rules/", len(parts)))
+	})
+
+	api.OnBeforeAgentStart(func(_ ext.BeforeAgentStartEvent, ctx ext.Context) *ext.BeforeAgentStartResult {
+		if rules == "" {
+			return nil
+		}
+		return &ext.BeforeAgentStartResult{
+			SystemPrompt: &rules,
+		}
+	})
+}

examples/extensions/protected-paths.go

@@ -0,0 +1,114 @@
+//go:build ignore
+
+package main
+
+import (
+	"encoding/json"
+	"strings"
+
+	"kit/ext"
+)
+
+// Init blocks tool calls that attempt to write, edit, or delete files in
+// protected paths.
+//
+// Protected: .env*, .git/, secrets/, credentials*, *.pem, *.key
+//
+// Usage: kit -e examples/extensions/protected-paths.go
+func Init(api ext.API) {
+	// Tools that modify files.
+	writeTools := map[string]bool{
+		"Write": true,
+		"Edit":  true,
+		"Bash":  true,
+	}
+
+	// Path patterns to protect (checked against the file_path / filePath field).
+	protectedPatterns := []string{
+		".env",
+		".git/",
+		"secrets/",
+		"credentials",
+		".pem",
+		".key",
+		"id_rsa",
+		"id_ed25519",
+	}
+
+	// Bash commands that could modify protected files.
+	bashWritePatterns := []string{
+		"rm ", "mv ", "cp ", "> ",
+		"cat >", "echo >", "tee ",
+		"chmod ", "chown ",
+	}
+
+	isProtected := func(path string) bool {
+		lower := strings.ToLower(path)
+		for _, p := range protectedPatterns {
+			if strings.Contains(lower, p) {
+				return true
+			}
+		}
+		return false
+	}
+
+	api.OnToolCall(func(tc ext.ToolCallEvent, ctx ext.Context) *ext.ToolCallResult {
+		if !writeTools[tc.ToolName] {
+			return nil
+		}
+
+		// For Write/Edit: check the file_path / filePath field.
+		if tc.ToolName == "Write" || tc.ToolName == "Edit" {
+			var input map[string]any
+			if err := json.Unmarshal([]byte(tc.Input), &input); err != nil {
+				return nil
+			}
+			// Try both naming conventions.
+			filePath, _ := input["file_path"].(string)
+			if filePath == "" {
+				filePath, _ = input["filePath"].(string)
+			}
+			if isProtected(filePath) {
+				return &ext.ToolCallResult{
+					Block:  true,
+					Reason: "Blocked: writing to protected path: " + filePath,
+				}
+			}
+			return nil
+		}
+
+		// For Bash: check if the command references protected paths.
+		if tc.ToolName == "Bash" {
+			var input struct {
+				Command string `json:"command"`
+			}
+			if err := json.Unmarshal([]byte(tc.Input), &input); err != nil {
+				return nil
+			}
+
+			// Only check bash commands that look like file mutations.
+			isMutation := false
+			for _, pat := range bashWritePatterns {
+				if strings.Contains(input.Command, pat) {
+					isMutation = true
+					break
+				}
+			}
+			if !isMutation {
+				return nil
+			}
+
+			// Check if any protected pattern appears in the command.
+			for _, p := range protectedPatterns {
+				if strings.Contains(input.Command, p) {
+					return &ext.ToolCallResult{
+						Block:  true,
+						Reason: "Blocked: bash command references protected path (" + p + "): " + input.Command,
+					}
+				}
+			}
+		}
+
+		return nil
+	})
+}

examples/extensions/status-tools/helpers.go

@@ -0,0 +1,43 @@
+//go:build ignore
+
+package main
+
+import (
+	"fmt"
+	"kit/ext"
+)
+
+// Helper functions for the status-tools extension
+// These are used by main.go but kept in a separate file
+// to demonstrate the multi-file extension pattern.
+
+// formatMemory converts bytes to human-readable format
+func formatMemory(bytes int64) string {
+	const (
+		KB = 1024
+		MB = 1024 * KB
+		GB = 1024 * MB
+	)
+
+	switch {
+	case bytes >= GB:
+		return fmt.Sprintf("%.2f GB", float64(bytes)/float64(GB))
+	case bytes >= MB:
+		return fmt.Sprintf("%.2f MB", float64(bytes)/float64(MB))
+	case bytes >= KB:
+		return fmt.Sprintf("%.2f KB", float64(bytes)/float64(KB))
+	default:
+		return fmt.Sprintf("%d B", bytes)
+	}
+}
+
+// showMemoryStatus displays memory usage (placeholder)
+func showMemoryStatus(ctx ext.Context) {
+	// This is a placeholder that would show memory stats
+	// In a real extension, you'd integrate with system metrics
+	ctx.PrintBlock(ext.PrintBlockOpts{
+		Text:        "Memory status monitoring not yet implemented",
+		BorderColor: "#f9e2af",
+		Subtitle:    "Memory",
+	})
+}

examples/extensions/status-tools/main.go

@@ -0,0 +1,49 @@
+//go:build ignore
+
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"kit/ext"
+)
+
+// Init registers the status tools extension.
+// This extension provides multiple status-related utilities as a
+// multi-file extension example.
+func Init(api ext.API) {
+	// Register a status bar widget that shows time
+	api.OnSessionStart(func(_ ext.SessionStartEvent, ctx ext.Context) {
+		go func() {
+			ticker := time.NewTicker(time.Second)
+			defer ticker.Stop()
+			for range ticker.C {
+				ctx.SetStatus("clock", time.Now().Format("15:04:05"), 5)
+			}
+		}()
+	})
+
+	// Register a /status command
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "status",
+		Description: "Show system status information",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			stats := ctx.GetContextStats()
+			info := fmt.Sprintf(
+				"Model: %s\nTokens: %d/%d (%.1f%%)\nMessages: %d",
+				ctx.Model,
+				stats.EstimatedTokens,
+				stats.ContextLimit,
+				stats.UsagePercent*100,
+				stats.MessageCount,
+			)
+			ctx.PrintBlock(ext.PrintBlockOpts{
+				Text:        info,
+				BorderColor: "#89b4fa",
+				Subtitle:    "System Status",
+			})
+			return "", nil
+		},
+	})
+}

examples/extensions/subagent-monitor_test.go

@@ -0,0 +1,159 @@
+package main
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/mark3labs/kit/internal/extensions"
+	"github.com/mark3labs/kit/pkg/extensions/test"
+)
+
+// TestSubagentMonitor_SessionStart verifies OnSessionStart initializes state
+// without panicking and properly guards nil ctx calls.
+func TestSubagentMonitor_SessionStart(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("../../.kit/extensions/subagent-monitor.go")
+
+	// Emit SessionStart - should not panic even with nil ctx functions
+	_, err := harness.Emit(extensions.SessionStartEvent{SessionID: "test-session"})
+	if err != nil {
+		t.Fatalf("SessionStart should not error: %v", err)
+	}
+}
+
+// TestSubagentMonitor_SubagentLifecycle verifies the full subagent lifecycle
+// creates entries and emits widget updates.
+func TestSubagentMonitor_SubagentLifecycle(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("../../.kit/extensions/subagent-monitor.go")
+
+	// Start session
+	_, err := harness.Emit(extensions.SessionStartEvent{SessionID: "test-session"})
+	if err != nil {
+		t.Fatalf("SessionStart should not error: %v", err)
+	}
+
+	// Emit SubagentStart
+	_, err = harness.Emit(extensions.SubagentStartEvent{
+		ToolCallID: "call-1",
+		Task:       "test task",
+	})
+	if err != nil {
+		t.Fatalf("SubagentStart should not error: %v", err)
+	}
+
+	// Emit a few chunks
+	for i := range 3 {
+		_, err = harness.Emit(extensions.SubagentChunkEvent{
+			ToolCallID: "call-1",
+			Task:       "test task",
+			ChunkType:  "text",
+			Content:    fmt.Sprintf("line %d", i),
+		})
+		if err != nil {
+			t.Fatalf("SubagentChunk %d should not error: %v", i, err)
+		}
+	}
+
+	// Emit tool call chunk
+	_, err = harness.Emit(extensions.SubagentChunkEvent{
+		ToolCallID: "call-1",
+		Task:       "test task",
+		ChunkType:  "tool_call",
+		ToolName:   "bash",
+	})
+	if err != nil {
+		t.Fatalf("SubagentChunk tool_call should not error: %v", err)
+	}
+
+	// Emit SubagentEnd
+	_, err = harness.Emit(extensions.SubagentEndEvent{
+		ToolCallID: "call-1",
+		Task:       "test task",
+		Response:   "done",
+	})
+	if err != nil {
+		t.Fatalf("SubagentEnd should not error: %v", err)
+	}
+
+	// Give time for cleanup goroutine
+	time.Sleep(100 * time.Millisecond)
+}
+
+// TestSubagentMonitor_MultipleSubagents verifies multiple parallel subagents.
+func TestSubagentMonitor_MultipleSubagents(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("../../.kit/extensions/subagent-monitor.go")
+
+	_, err := harness.Emit(extensions.SessionStartEvent{SessionID: "test-session"})
+	if err != nil {
+		t.Fatalf("SessionStart should not error: %v", err)
+	}
+
+	// Start 3 subagents
+	for i := 1; i <= 3; i++ {
+		_, err := harness.Emit(extensions.SubagentStartEvent{
+			ToolCallID: fmt.Sprintf("call-%d", i),
+			Task:       fmt.Sprintf("task %d", i),
+		})
+		if err != nil {
+			t.Fatalf("SubagentStart %d should not error: %v", i, err)
+		}
+	}
+
+	// Emit chunks for each
+	for i := 1; i <= 3; i++ {
+		_, err := harness.Emit(extensions.SubagentChunkEvent{
+			ToolCallID: fmt.Sprintf("call-%d", i),
+			Task:       fmt.Sprintf("task %d", i),
+			ChunkType:  "text",
+			Content:    fmt.Sprintf("output from agent %d", i),
+		})
+		if err != nil {
+			t.Fatalf("SubagentChunk %d should not error: %v", i, err)
+		}
+	}
+
+	// End all subagents
+	for i := 1; i <= 3; i++ {
+		_, err := harness.Emit(extensions.SubagentEndEvent{
+			ToolCallID: fmt.Sprintf("call-%d", i),
+			Task:       fmt.Sprintf("task %d", i),
+			Response:   "completed",
+		})
+		if err != nil {
+			t.Fatalf("SubagentEnd %d should not error: %v", i, err)
+		}
+	}
+
+	time.Sleep(100 * time.Millisecond)
+}
+
+// TestSubagentMonitor_SessionShutdown verifies shutdown doesn't panic
+// even with nil ctx functions.
+func TestSubagentMonitor_SessionShutdown(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("../../.kit/extensions/subagent-monitor.go")
+
+	// Start then shutdown
+	_, err := harness.Emit(extensions.SessionStartEvent{SessionID: "test-session"})
+	if err != nil {
+		t.Fatalf("SessionStart should not error: %v", err)
+	}
+
+	// Start a subagent
+	_, err = harness.Emit(extensions.SubagentStartEvent{
+		ToolCallID: "call-1",
+		Task:       "test task",
+	})
+	if err != nil {
+		t.Fatalf("SubagentStart should not error: %v", err)
+	}
+
+	// Shutdown - should not panic even with active subagent
+	_, err = harness.Emit(extensions.SessionShutdownEvent{})
+	if err != nil {
+		t.Fatalf("SessionShutdown should not error: %v", err)
+	}
+}

examples/extensions/subagent-test.go

@@ -0,0 +1,164 @@
+//go:build ignore
+
+// Subagent Test Extension — Tests the new first-class subagent API
+//
+// Commands:
+//
+//	/subtest <task>      — spawn a blocking subagent and print result
+//	/subbg <task>        — spawn a background subagent with live output
+//
+// Usage: kit -e examples/extensions/subagent-test.go
+package main
+
+import (
+	"fmt"
+	"strings"
+	"sync"
+	"time"
+
+	"kit/ext"
+)
+
+var (
+	mu        sync.Mutex
+	latestCtx ext.Context
+	hasCtx    bool
+)
+
+func Init(api ext.API) {
+	// Keep context fresh
+	api.OnSessionStart(func(_ ext.SessionStartEvent, ctx ext.Context) {
+		mu.Lock()
+		latestCtx = ctx
+		hasCtx = true
+		mu.Unlock()
+
+		ctx.PrintInfo(
+			"Subagent Test Extension loaded\n\n" +
+				"/subtest <task>    Spawn blocking subagent\n" +
+				"/subbg <task>      Spawn background subagent\n\n" +
+				"The LLM can also use the spawn_subagent tool.")
+	})
+
+	api.OnAgentEnd(func(_ ext.AgentEndEvent, ctx ext.Context) {
+		mu.Lock()
+		latestCtx = ctx
+		mu.Unlock()
+	})
+
+	// Command: /subtest <task> — blocking subagent
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "subtest",
+		Description: "Spawn a blocking subagent: /subtest <task>",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			mu.Lock()
+			latestCtx = ctx
+			hasCtx = true
+			mu.Unlock()
+
+			task := strings.TrimSpace(args)
+			if task == "" {
+				return "Usage: /subtest <task>", nil
+			}
+
+			ctx.PrintInfo(fmt.Sprintf("Spawning blocking subagent for: %s", task))
+
+			start := time.Now()
+			_, result, err := ctx.SpawnSubagent(ext.SubagentConfig{
+				Prompt:   task,
+				Timeout:  2 * time.Minute,
+				Blocking: true,
+			})
+			elapsed := time.Since(start)
+
+			if err != nil {
+				return fmt.Sprintf("Spawn error: %v", err), nil
+			}
+
+			if result == nil {
+				return "No result returned", nil
+			}
+
+			if result.Error != nil {
+				return fmt.Sprintf("Subagent failed (exit %d) after %ds: %v\n\nPartial output:\n%s",
+					result.ExitCode, int(elapsed.Seconds()), result.Error, truncate(result.Response, 2000)), nil
+			}
+
+			response := fmt.Sprintf("Subagent completed in %ds", int(elapsed.Seconds()))
+			if result.Usage != nil {
+				response += fmt.Sprintf(" (tokens: %d in / %d out)", result.Usage.InputTokens, result.Usage.OutputTokens)
+			}
+			response += fmt.Sprintf("\n\nResult:\n%s", truncate(result.Response, 4000))
+
+			return response, nil
+		},
+	})
+
+	// Command: /subbg <task> — background subagent with callbacks
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "subbg",
+		Description: "Spawn a background subagent: /subbg <task>",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			mu.Lock()
+			latestCtx = ctx
+			hasCtx = true
+			mu.Unlock()
+
+			task := strings.TrimSpace(args)
+			if task == "" {
+				return "Usage: /subbg <task>", nil
+			}
+
+			ctx.PrintInfo(fmt.Sprintf("Spawning background subagent for: %s", task))
+
+			start := time.Now()
+			handle, _, err := ctx.SpawnSubagent(ext.SubagentConfig{
+				Prompt:  task,
+				Timeout: 2 * time.Minute,
+				OnOutput: func(chunk string) {
+					// Live output - could update a widget here
+					fmt.Print(chunk)
+				},
+				OnComplete: func(result ext.SubagentResult) {
+					elapsed := time.Since(start)
+
+					mu.Lock()
+					c := latestCtx
+					ok := hasCtx
+					mu.Unlock()
+
+					if !ok {
+						return
+					}
+
+					if result.Error != nil {
+						c.SendMessage(fmt.Sprintf("Background subagent failed after %ds: %v",
+							int(elapsed.Seconds()), result.Error))
+						return
+					}
+
+					msg := fmt.Sprintf("Background subagent completed in %ds", int(elapsed.Seconds()))
+					if result.Usage != nil {
+						msg += fmt.Sprintf(" (tokens: %d in / %d out)", result.Usage.InputTokens, result.Usage.OutputTokens)
+					}
+					msg += fmt.Sprintf("\n\nResult:\n%s", truncate(result.Response, 4000))
+
+					c.SendMessage(msg)
+				},
+			})
+
+			if err != nil {
+				return fmt.Sprintf("Spawn error: %v", err), nil
+			}
+
+			return fmt.Sprintf("Background subagent spawned (ID: %s). Results will be delivered when complete.", handle.ID), nil
+		},
+	})
+}
+
+func truncate(s string, max int) string {
+	if len(s) <= max {
+		return s
+	}
+	return s[:max] + "\n\n... [truncated]"
+}

examples/extensions/subagent-widget.go

@@ -35,6 +35,11 @@ import (
 	"kit/ext"
 )
 
+// subJSONOutput matches the JSON envelope produced by `kit --json`.
+type subJSONOutput struct {
+	Response string `json:"response"`
+}
+
 // ---------------------------------------------------------------------------
 // Types
 // ---------------------------------------------------------------------------
@@ -204,10 +209,10 @@ func spawnAgent(state *subState) {
 	}
 
 	args := []string{
-		"--prompt", prompt,
-		"--quiet",
+		"--json",
 		"--no-session",
 		"--no-extensions",
+		prompt,
 	}
 
 	cmd := exec.Command(kitBinary, args...)
@@ -261,7 +266,7 @@ func spawnAgent(state *subState) {
 		}
 	}()
 
-	// Read stderr in background goroutine.
+	// Read stderr in background goroutine (live widget updates).
 	var readWg sync.WaitGroup
 	readWg.Add(1)
 	go func() {
@@ -277,12 +282,12 @@ func spawnAgent(state *subState) {
 		}
 	}()
 
-	// Read stdout in foreground.
+	// Read stdout into a separate buffer (JSON output from --json mode).
+	var stdoutBuf strings.Builder
 	scanner := bufio.NewScanner(stdout)
 	scanner.Buffer(make([]byte, 256*1024), 256*1024)
 	for scanner.Scan() {
-		state.appendChunk(scanner.Text() + "\n")
-		updateWidgets()
+		stdoutBuf.WriteString(scanner.Text() + "\n")
 	}
 
 	// Wait for all pipe readers, then the process.
@@ -290,6 +295,17 @@ func spawnAgent(state *subState) {
 	waitErr := cmd.Wait()
 	close(doneCh) // stop timer
 
+	// Parse JSON output from --json mode to extract the response.
+	var result string
+	rawStdout := strings.TrimSpace(stdoutBuf.String())
+	var parsed subJSONOutput
+	if rawStdout != "" && json.Unmarshal([]byte(rawStdout), &parsed) == nil && parsed.Response != "" {
+		result = parsed.Response
+	} else {
+		// Fallback: use raw stdout (e.g. older kit binary without --json).
+		result = rawStdout
+	}
+
 	state.mu.Lock()
 	state.Elapsed = time.Since(start)
 	state.Proc = nil
@@ -298,7 +314,6 @@ func spawnAgent(state *subState) {
 	} else {
 		state.Status = "done"
 	}
-	result := strings.Join(state.Chunks, "")
 
 	// Save history for /subcont continuations (cap at 16 KB).
 	state.History += fmt.Sprintf("\n--- Turn %d ---\nTask: %s\nResult:\n%s\n",

examples/extensions/summarize.go

@@ -0,0 +1,93 @@
+//go:build ignore
+
+package main
+
+import (
+	"fmt"
+	"strings"
+
+	"kit/ext"
+)
+
+// Init adds a /summarize command that generates a concise summary of the
+// current conversation using a direct LLM completion. Demonstrates the
+// ctx.Complete API.
+//
+// The summary is displayed in a styled block and can optionally be saved
+// to the session via AppendEntry for later retrieval.
+//
+// Usage: kit -e examples/extensions/summarize.go
+func Init(api ext.API) {
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "summarize",
+		Description: "Summarize the current conversation",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			msgs := ctx.GetMessages()
+			if len(msgs) == 0 {
+				ctx.PrintInfo("Nothing to summarize — no messages yet.")
+				return "", nil
+			}
+
+			// Build a text representation of the conversation.
+			var parts []string
+			for _, m := range msgs {
+				content := m.Content
+				if len(content) > 2000 {
+					content = content[:1997] + "..."
+				}
+				parts = append(parts, fmt.Sprintf("[%s]: %s", m.Role, content))
+			}
+			conversation := strings.Join(parts, "\n\n")
+
+			ctx.PrintInfo("Generating summary...")
+
+			resp, err := ctx.Complete(ext.CompleteRequest{
+				System: `You are a concise summarization assistant. Summarize the conversation below in 3-5 bullet points. Focus on:
+- What was discussed or requested
+- Key decisions or outcomes
+- Any pending action items
+
+Be concise. Use plain text, no markdown headers.`,
+				Prompt: conversation,
+			})
+			if err != nil {
+				ctx.PrintError("Summary failed: " + err.Error())
+				return "", nil
+			}
+
+			summary := strings.TrimSpace(resp.Text)
+
+			ctx.PrintBlock(ext.PrintBlockOpts{
+				Text:        summary,
+				BorderColor: "#89b4fa",
+				Subtitle:    fmt.Sprintf("Summary (%d messages, %d tokens used)", len(msgs), resp.InputTokens+resp.OutputTokens),
+			})
+
+			// Persist the summary in the session for later retrieval.
+			ctx.AppendEntry("summary", summary)
+
+			return "", nil
+		},
+	})
+
+	// /summaries — list all saved summaries.
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "summaries",
+		Description: "List saved conversation summaries",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			entries := ctx.GetEntries("summary")
+			if len(entries) == 0 {
+				ctx.PrintInfo("No summaries saved yet. Use /summarize to create one.")
+				return "", nil
+			}
+			for i, e := range entries {
+				ctx.PrintBlock(ext.PrintBlockOpts{
+					Text:        e.Data,
+					BorderColor: "#89b4fa",
+					Subtitle:    fmt.Sprintf("Summary #%d (%s)", i+1, e.Timestamp[:19]),
+				})
+			}
+			return "", nil
+		},
+	})
+}

examples/extensions/tool-logger_test.go

@@ -0,0 +1,358 @@
+package main
+
+import (
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/mark3labs/kit/internal/extensions"
+	"github.com/mark3labs/kit/pkg/extensions/test"
+)
+
+// Test that the tool-logger extension loads and registers handlers
+func TestToolLogger_Loads(t *testing.T) {
+	harness := test.New(t)
+	ext := harness.LoadFile("tool-logger.go")
+
+	if ext == nil {
+		t.Fatal("extension should not be nil")
+	}
+
+	// Verify all expected handlers are registered
+	test.AssertHasHandlers(t, harness, extensions.ToolCall)
+	test.AssertHasHandlers(t, harness, extensions.ToolResult)
+	test.AssertHasHandlers(t, harness, extensions.SessionStart)
+	test.AssertHasHandlers(t, harness, extensions.SessionShutdown)
+	test.AssertHasHandlers(t, harness, extensions.Input)
+}
+
+// Test that tool calls are logged (handlers run without errors)
+func TestToolLogger_ToolCall(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	// Emit a tool call event
+	result, err := harness.Emit(extensions.ToolCallEvent{
+		ToolName:   "Read",
+		ToolCallID: "call-123",
+		Input:      `{"file": "test.txt"}`,
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Tool logger should not block any tools
+	test.AssertNotBlocked(t, result)
+}
+
+// Test that tool results are processed
+func TestToolLogger_ToolResult(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	content := "Hello, World!"
+	result, err := harness.Emit(extensions.ToolResultEvent{
+		ToolName: "Read",
+		Content:  content,
+		IsError:  false,
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Tool logger should not modify results
+	if result != nil {
+		t.Error("expected nil result (no modification)")
+	}
+}
+
+// Test that error tool results are handled
+func TestToolLogger_ToolResultError(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	result, err := harness.Emit(extensions.ToolResultEvent{
+		ToolName: "Bash",
+		Content:  "command not found",
+		IsError:  true,
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if result != nil {
+		t.Error("expected nil result (no modification)")
+	}
+}
+
+// Test session start handler
+func TestToolLogger_SessionStart(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	_, err := harness.Emit(extensions.SessionStartEvent{
+		SessionID: "test-session-123",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Handler should run without errors (logs to file)
+	// Since file logging happens outside our mock, we just verify no errors
+}
+
+// Test session shutdown handler
+func TestToolLogger_SessionShutdown(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	_, err := harness.Emit(extensions.SessionShutdownEvent{})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+// Test the !time command
+func TestToolLogger_TimeCommand(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	result, err := harness.Emit(extensions.InputEvent{
+		Text:   "!time",
+		Source: "cli",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	test.AssertInputHandled(t, result, "handled")
+
+	// Verify PrintInfo was called with a time message
+	infos := harness.Context().GetPrintInfos()
+	found := false
+	for _, info := range infos {
+		if strings.Contains(info, "Current time:") {
+			found = true
+			break
+		}
+	}
+	if !found {
+		t.Errorf("expected PrintInfo with 'Current time:', got: %v", infos)
+	}
+}
+
+// Test the !status command
+func TestToolLogger_StatusCommand(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	result, err := harness.Emit(extensions.InputEvent{
+		Text:   "!status",
+		Source: "cli",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	test.AssertInputHandled(t, result, "handled")
+
+	// Verify PrintBlock was called
+	blocks := harness.Context().PrintBlocks
+	if len(blocks) != 1 {
+		t.Fatalf("expected 1 PrintBlock call, got %d", len(blocks))
+	}
+
+	block := blocks[0]
+	if block.Subtitle != "tool-logger extension" {
+		t.Errorf("expected subtitle 'tool-logger extension', got %q", block.Subtitle)
+	}
+	if block.BorderColor != "#a6e3a1" {
+		t.Errorf("expected border color '#a6e3a1', got %q", block.BorderColor)
+	}
+	if !strings.Contains(block.Text, "Session active") {
+		t.Errorf("expected text to contain 'Session active', got %q", block.Text)
+	}
+}
+
+// Test that unknown commands are not handled
+func TestToolLogger_UnknownCommand(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	result, err := harness.Emit(extensions.InputEvent{
+		Text:   "!unknown",
+		Source: "cli",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if result != nil {
+		t.Errorf("expected nil result for unknown command, got %v", result)
+	}
+
+	// Verify no info/block prints for unknown commands
+	if len(harness.Context().GetPrintInfos()) != 0 {
+		t.Error("expected no PrintInfo calls for unknown command")
+	}
+	if len(harness.Context().PrintBlocks) != 0 {
+		t.Error("expected no PrintBlock calls for unknown command")
+	}
+}
+
+// Test regular text input (not a command)
+func TestToolLogger_RegularInput(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	result, err := harness.Emit(extensions.InputEvent{
+		Text:   "This is a normal message",
+		Source: "cli",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if result != nil {
+		t.Errorf("expected nil result for regular input, got %v", result)
+	}
+}
+
+// Test complete session flow
+func TestToolLogger_FullSession(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	// Simulate a full session
+	_, err := harness.Emit(extensions.SessionStartEvent{SessionID: "test"})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Several tool calls
+	tools := []string{"Read", "Glob", "Grep", "Bash"}
+	for _, tool := range tools {
+		_, err := harness.Emit(extensions.ToolCallEvent{
+			ToolName: tool,
+			Input:    "{}",
+		})
+		if err != nil {
+			t.Fatalf("error for tool %s: %v", tool, err)
+		}
+
+		_, err = harness.Emit(extensions.ToolResultEvent{
+			ToolName: tool,
+			Content:  "result",
+			IsError:  false,
+		})
+		if err != nil {
+			t.Fatalf("error for tool result %s: %v", tool, err)
+		}
+	}
+
+	// User issues a command
+	_, err = harness.Emit(extensions.InputEvent{Text: "!time", Source: "cli"})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	_, err = harness.Emit(extensions.SessionShutdownEvent{})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Verify the !time command was handled
+	if len(harness.Context().GetPrintInfos()) != 1 {
+		t.Errorf("expected 1 PrintInfo call, got %d", len(harness.Context().GetPrintInfos()))
+	}
+}
+
+// Test that the extension handles file write errors gracefully
+func TestToolLogger_FileError(t *testing.T) {
+	// This test verifies the extension doesn't panic when file operations fail
+	// Since we can't easily mock os.OpenFile, we rely on the extension code
+	// properly checking for errors (which it does)
+
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	// Just verify the handlers run without panicking
+	_, err := harness.Emit(extensions.ToolCallEvent{ToolName: "Read", Input: "{}"})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	_, err = harness.Emit(extensions.SessionStartEvent{SessionID: "test"})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+// Test concurrent tool calls (race condition check)
+func TestToolLogger_ConcurrentToolCalls(t *testing.T) {
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	// Run multiple tool calls concurrently
+	done := make(chan bool, 10)
+	for i := range 10 {
+		go func(index int) {
+			defer func() { done <- true }()
+
+			toolName := "Tool" + string(rune('0'+index))
+			_, err := harness.Emit(extensions.ToolCallEvent{
+				ToolName: toolName,
+				Input:    "{}",
+			})
+			if err != nil {
+				t.Errorf("error in goroutine %d: %v", index, err)
+			}
+		}(i)
+	}
+
+	// Wait for all goroutines
+	for range 10 {
+		<-done
+	}
+}
+
+// Test the actual log file is created and written to
+func TestToolLogger_LogFile(t *testing.T) {
+	logFile := "/tmp/kit-tool-log.txt"
+
+	// Clean up before test
+	_ = os.Remove(logFile)
+
+	harness := test.New(t)
+	harness.LoadFile("tool-logger.go")
+
+	// Emit events
+	_, _ = harness.Emit(extensions.SessionStartEvent{SessionID: "test"})
+	_, _ = harness.Emit(extensions.ToolCallEvent{ToolName: "Read", Input: "{}"})
+	_, _ = harness.Emit(extensions.ToolResultEvent{ToolName: "Read", Content: "data", IsError: false})
+
+	// Note: Since the extension writes to a real file and the test harness
+	// mocks the context, the file writes actually happen. Let's verify.
+
+	// Give it a moment for file operations
+	if _, err := os.Stat(logFile); err == nil {
+		// File exists - read and verify content
+		content, err := os.ReadFile(logFile)
+		if err != nil {
+			t.Logf("Could not read log file: %v", err)
+		} else {
+			contentStr := string(content)
+			if !strings.Contains(contentStr, "SESSION_START") {
+				t.Error("log file should contain SESSION_START")
+			}
+			if !strings.Contains(contentStr, "CALL tool=Read") {
+				t.Error("log file should contain CALL tool=Read")
+			}
+			if !strings.Contains(contentStr, "RESULT tool=Read") {
+				t.Error("log file should contain RESULT tool=Read")
+			}
+		}
+	} else {
+		t.Log("Note: Log file not created - this is expected since the extension writes directly to disk")
+	}
+}

examples/extensions/tool-renderer-demo.go

@@ -28,7 +28,7 @@ func Init(api ext.API) {
 		DisplayName: "File",
 		BorderColor: "#89b4fa", // Catppuccin blue
 		RenderHeader: func(toolArgs string, width int) string {
-			var args map[string]interface{}
+			var args map[string]any
 			if err := json.Unmarshal([]byte(toolArgs), &args); err != nil {
 				return ""
 			}
@@ -72,7 +72,7 @@ func Init(api ext.API) {
 		Background:  "#1e1e2e", // Dark background
 		BorderColor: "#a6e3a1", // Catppuccin green
 		RenderHeader: func(toolArgs string, width int) string {
-			var args map[string]interface{}
+			var args map[string]any
 			if err := json.Unmarshal([]byte(toolArgs), &args); err != nil {
 				return ""
 			}

examples/sdk/README.md

@@ -0,0 +1,45 @@
+# SDK Examples
+
+These examples demonstrate how to use the Kit SDK (`pkg/kit`) to build agents programmatically in Go.
+
+## Examples
+
+### [basic](basic/)
+
+Shows core SDK usage: creating a Kit instance, sending prompts, overriding the model, subscribing to events (tool calls, streaming), and session management.
+
+```bash
+go run ./examples/sdk/basic
+```
+
+### [scripting](scripting/)
+
+A minimal script-friendly wrapper that takes a prompt from the command line and prints the response — useful for piping and automation.
+
+```bash
+go run ./examples/sdk/scripting "Explain what this repo does"
+```
+
+### [crypto-monitor](crypto-monitor/)
+
+A background agent that checks Bitcoin and Ethereum prices every 30 minutes and sends desktop notifications via `notify-send` (dbus). Demonstrates using the SDK for a long-running autonomous task with a single tool.
+
+```bash
+go run ./examples/sdk/crypto-monitor
+
+# Override the check interval:
+CRYPTO_INTERVAL=5m go run ./examples/sdk/crypto-monitor
+```
+
+## Getting Started
+
+```go
+import kit "github.com/mark3labs/kit/pkg/kit"
+
+host, err := kit.New(ctx, nil)        // uses ~/.kit.yml defaults
+defer host.Close()
+
+response, err := host.Prompt(ctx, "Hello!")
+```
+
+See the [SDK README](../../pkg/kit/README.md) for the full API reference.

examples/sdk/crypto-monitor/main.go

@@ -0,0 +1,85 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"os/signal"
+	"time"
+
+	kit "github.com/mark3labs/kit/pkg/kit"
+)
+
+const systemPrompt = `You are a cryptocurrency price monitor. Your job is to:
+
+1. Fetch the current prices of Bitcoin and Ethereum using bash with curl
+2. Send a desktop notification with the results using notify-send
+
+To fetch prices, use this CoinGecko API endpoint (no API key needed):
+  curl -s 'https://api.coingecko.com/api/v3/simple/price?ids=bitcoin,ethereum&vs_currencies=usd&include_24hr_change=true'
+
+To send a desktop notification:
+  notify-send -i dialog-information "Crypto Prices" "BTC: $XX,XXX (+X.X%)\nETH: $X,XXX (+X.X%)"
+
+Include the 24h percentage change in the notification. Use a green arrow (▲) for
+positive changes and a red arrow (▼) for negative. Format prices with commas.
+
+If the API call fails, send a notification about the failure instead.
+
+Always complete both steps: fetch then notify. Be concise — no commentary needed.`
+
+func main() {
+	interval := 30 * time.Minute
+	if os.Getenv("CRYPTO_INTERVAL") != "" {
+		d, err := time.ParseDuration(os.Getenv("CRYPTO_INTERVAL"))
+		if err == nil {
+			interval = d
+		}
+	}
+
+	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
+	defer cancel()
+
+	host, err := kit.New(ctx, &kit.Options{
+		SystemPrompt: systemPrompt,
+		Tools:        []kit.Tool{kit.NewBashTool()},
+		NoSession:    true,
+		Quiet:        true,
+	})
+	if err != nil {
+		log.Fatalf("Failed to create kit instance: %v", err)
+	}
+	defer func() { _ = host.Close() }()
+
+	fmt.Printf("Crypto price monitor started (every %s)\n", interval)
+	fmt.Println("Press Ctrl+C to stop")
+
+	// Run immediately on startup, then on each tick.
+	check(ctx, host)
+
+	ticker := time.NewTicker(interval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			check(ctx, host)
+		case <-ctx.Done():
+			fmt.Println("\nStopping price monitor")
+			return
+		}
+	}
+}
+
+func check(ctx context.Context, host *kit.Kit) {
+	fmt.Printf("[%s] Checking prices...\n", time.Now().Format("15:04:05"))
+
+	// Clear session so each check is independent.
+	host.ClearSession()
+
+	_, err := host.Prompt(ctx, "Fetch current Bitcoin and Ethereum prices and send a desktop notification.")
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+	}
+}

go.mod

@@ -1,94 +1,99 @@
 module github.com/mark3labs/kit
 
-go 1.26.0
+go 1.26.1
 
 require (
 	charm.land/bubbles/v2 v2.0.0
-	charm.land/bubbletea/v2 v2.0.0
-	charm.land/fantasy v0.10.0
-	charm.land/lipgloss/v2 v2.0.0
-	github.com/charmbracelet/fang v0.4.4
-	github.com/mark3labs/mcp-go v0.44.0
+	charm.land/bubbletea/v2 v2.0.2
+	charm.land/fantasy v0.17.1
+	charm.land/huh/v2 v2.0.3
+	charm.land/lipgloss/v2 v2.0.2
+	github.com/alecthomas/chroma/v2 v2.23.1
+	github.com/aymanbagabas/go-udiff v0.4.1
+	github.com/charmbracelet/fang v1.0.0
+	github.com/charmbracelet/log v1.0.0
+	github.com/coder/acp-go-sdk v0.6.3
+	github.com/mark3labs/mcp-go v0.46.0
 	github.com/spf13/cobra v1.10.2
 	github.com/spf13/viper v1.21.0
-	golang.org/x/term v0.40.0
+	github.com/traefik/yaegi v0.16.1
+	golang.org/x/term v0.41.0
 	gopkg.in/yaml.v3 v3.0.1
 )
 
 require (
 	cloud.google.com/go v0.123.0 // indirect
-	cloud.google.com/go/auth v0.18.2 // indirect
+	cloud.google.com/go/auth v0.19.0 // indirect
 	cloud.google.com/go/auth/oauth2adapt v0.2.8 // indirect
 	cloud.google.com/go/compute/metadata v0.9.0 // indirect
 	github.com/Azure/azure-sdk-for-go/sdk/azcore v1.21.0 // indirect
 	github.com/Azure/azure-sdk-for-go/sdk/internal v1.11.2 // indirect
-	github.com/alecthomas/chroma/v2 v2.23.1 // indirect
 	github.com/atotto/clipboard v0.1.4 // indirect
-	github.com/aws/aws-sdk-go-v2 v1.41.2 // indirect
-	github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.7.5 // indirect
-	github.com/aws/aws-sdk-go-v2/config v1.32.10 // indirect
-	github.com/aws/aws-sdk-go-v2/credentials v1.19.10 // indirect
-	github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.18.18 // indirect
-	github.com/aws/aws-sdk-go-v2/internal/configsources v1.4.18 // indirect
-	github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.7.18 // indirect
-	github.com/aws/aws-sdk-go-v2/internal/ini v1.8.4 // indirect
-	github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.13.5 // indirect
-	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.13.18 // indirect
-	github.com/aws/aws-sdk-go-v2/service/signin v1.0.6 // indirect
-	github.com/aws/aws-sdk-go-v2/service/sso v1.30.11 // indirect
-	github.com/aws/aws-sdk-go-v2/service/ssooidc v1.35.15 // indirect
-	github.com/aws/aws-sdk-go-v2/service/sts v1.41.7 // indirect
-	github.com/aws/smithy-go v1.24.1 // indirect
-	github.com/aymanbagabas/go-udiff v0.4.0 // indirect
+	github.com/aws/aws-sdk-go-v2 v1.41.4 // indirect
+	github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.7.8 // indirect
+	github.com/aws/aws-sdk-go-v2/config v1.32.12 // indirect
+	github.com/aws/aws-sdk-go-v2/credentials v1.19.12 // indirect
+	github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.18.20 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/configsources v1.4.20 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.7.20 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/ini v1.8.6 // indirect
+	github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.13.7 // indirect
+	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.13.20 // indirect
+	github.com/aws/aws-sdk-go-v2/service/signin v1.0.8 // indirect
+	github.com/aws/aws-sdk-go-v2/service/sso v1.30.13 // indirect
+	github.com/aws/aws-sdk-go-v2/service/ssooidc v1.35.17 // indirect
+	github.com/aws/aws-sdk-go-v2/service/sts v1.41.9 // indirect
+	github.com/aws/smithy-go v1.24.2 // indirect
 	github.com/aymerick/douceur v0.2.0 // indirect
-	github.com/bahlo/generic-list-go v0.2.0 // indirect
-	github.com/buger/jsonparser v1.1.1 // indirect
+	github.com/catppuccin/go v0.3.0 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/charmbracelet/anthropic-sdk-go v0.0.0-20260223140439-63879b0b8dab // indirect
-	github.com/charmbracelet/colorprofile v0.4.2 // indirect
+	github.com/charmbracelet/colorprofile v0.4.3 // indirect
 	github.com/charmbracelet/harmonica v0.2.0 // indirect
 	github.com/charmbracelet/lipgloss v1.1.1-0.20250404203927-76690c660834 // indirect
-	github.com/charmbracelet/log v0.4.2 // indirect
-	github.com/charmbracelet/ultraviolet v0.0.0-20260223171050-89c142e4aa73 // indirect
+	github.com/charmbracelet/openai-go v0.0.0-20260319145158-d0740cc34266 // indirect
+	github.com/charmbracelet/ultraviolet v0.0.0-20260316091819-b93f6a3b8502 // indirect
 	github.com/charmbracelet/x/cellbuf v0.0.15 // indirect
-	github.com/charmbracelet/x/exp/charmtone v0.0.0-20260223200540-d6a276319c45 // indirect
-	github.com/charmbracelet/x/exp/slice v0.0.0-20260223200540-d6a276319c45 // indirect
+	github.com/charmbracelet/x/exp/charmtone v0.0.0-20260323091123-df7b1bcffcca // indirect
+	github.com/charmbracelet/x/exp/ordered v0.1.0 // indirect
+	github.com/charmbracelet/x/exp/slice v0.0.0-20260323091123-df7b1bcffcca // indirect
+	github.com/charmbracelet/x/exp/strings v0.1.0 // indirect
 	github.com/charmbracelet/x/json v0.2.0 // indirect
 	github.com/charmbracelet/x/termios v0.1.1 // indirect
 	github.com/charmbracelet/x/windows v0.2.2 // indirect
 	github.com/clipperhouse/displaywidth v0.11.0 // indirect
 	github.com/clipperhouse/uax29/v2 v2.7.0 // indirect
 	github.com/dlclark/regexp2 v1.11.5 // indirect
+	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
 	github.com/go-json-experiment/json v0.0.0-20260214004413-d219187c3433 // indirect
-	github.com/go-logfmt/logfmt v0.6.0 // indirect
+	github.com/go-logfmt/logfmt v0.6.1 // indirect
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-viper/mapstructure/v2 v2.5.0 // indirect
 	github.com/goccy/go-yaml v1.19.2 // indirect
 	github.com/golang-jwt/jwt/v5 v5.3.0 // indirect
 	github.com/google/go-cmp v0.7.0 // indirect
+	github.com/google/jsonschema-go v0.4.2 // indirect
 	github.com/google/s2a-go v0.1.9 // indirect
 	github.com/google/uuid v1.6.0 // indirect
-	github.com/googleapis/enterprise-certificate-proxy v0.3.12 // indirect
-	github.com/googleapis/gax-go/v2 v2.17.0 // indirect
+	github.com/googleapis/enterprise-certificate-proxy v0.3.14 // indirect
+	github.com/googleapis/gax-go/v2 v2.20.0 // indirect
 	github.com/gorilla/css v1.0.1 // indirect
 	github.com/gorilla/websocket v1.5.3 // indirect
-	github.com/invopop/jsonschema v0.13.0 // indirect
-	github.com/kaptinlin/go-i18n v0.2.11 // indirect
-	github.com/kaptinlin/jsonpointer v0.4.16 // indirect
-	github.com/kaptinlin/jsonschema v0.7.3 // indirect
+	github.com/kaptinlin/go-i18n v0.2.12 // indirect
+	github.com/kaptinlin/jsonpointer v0.4.17 // indirect
+	github.com/kaptinlin/jsonschema v0.7.6 // indirect
 	github.com/kaptinlin/messageformat-go v0.4.18 // indirect
-	github.com/mailru/easyjson v0.9.1 // indirect
 	github.com/microcosm-cc/bluemonday v1.0.27 // indirect
+	github.com/mitchellh/hashstructure/v2 v2.0.2 // indirect
 	github.com/muesli/mango v0.2.0 // indirect
 	github.com/muesli/mango-cobra v1.3.0 // indirect
 	github.com/muesli/mango-pflag v0.2.0 // indirect
 	github.com/muesli/reflow v0.3.0 // indirect
 	github.com/muesli/roff v0.1.0 // indirect
-	github.com/openai/openai-go/v2 v2.7.1 // indirect
-	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
+	github.com/pelletier/go-toml/v2 v2.3.0 // indirect
 	github.com/sagikazarmark/locafero v0.12.0 // indirect
 	github.com/spf13/afero v1.15.0 // indirect
 	github.com/spf13/cast v1.10.0 // indirect
@@ -97,46 +102,44 @@ require (
 	github.com/tidwall/match v1.2.0 // indirect
 	github.com/tidwall/pretty v1.2.1 // indirect
 	github.com/tidwall/sjson v1.2.5 // indirect
-	github.com/traefik/yaegi v0.16.1 // indirect
-	github.com/wk8/go-ordered-map/v2 v2.1.8 // indirect
 	github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e // indirect
 	github.com/yosida95/uritemplate/v3 v3.0.2 // indirect
-	github.com/yuin/goldmark v1.7.16 // indirect
+	github.com/yuin/goldmark v1.8.2 // indirect
 	github.com/yuin/goldmark-emoji v1.0.6 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
-	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.65.0 // indirect
-	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.65.0 // indirect
-	go.opentelemetry.io/otel v1.40.0 // indirect
-	go.opentelemetry.io/otel/metric v1.40.0 // indirect
-	go.opentelemetry.io/otel/trace v1.40.0 // indirect
+	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.67.0 // indirect
+	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.67.0 // indirect
+	go.opentelemetry.io/otel v1.42.0 // indirect
+	go.opentelemetry.io/otel/metric v1.42.0 // indirect
+	go.opentelemetry.io/otel/trace v1.42.0 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
-	golang.org/x/crypto v0.48.0 // indirect
-	golang.org/x/exp v0.0.0-20260218203240-3dfff04db8fa // indirect
-	golang.org/x/net v0.50.0 // indirect
-	golang.org/x/oauth2 v0.35.0 // indirect
-	golang.org/x/time v0.14.0 // indirect
-	google.golang.org/api v0.269.0 // indirect
-	google.golang.org/genai v1.47.0 // indirect
-	google.golang.org/genproto/googleapis/rpc v0.0.0-20260223185530-2f722ef697dc // indirect
-	google.golang.org/grpc v1.79.1 // indirect
+	golang.org/x/crypto v0.49.0 // indirect
+	golang.org/x/exp v0.0.0-20260312153236-7ab1446f8b90 // indirect
+	golang.org/x/net v0.52.0 // indirect
+	golang.org/x/oauth2 v0.36.0 // indirect
+	golang.org/x/time v0.15.0 // indirect
+	google.golang.org/api v0.273.0 // indirect
+	google.golang.org/genai v1.51.0 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20260319201613-d00831a3d3e7 // indirect
+	google.golang.org/grpc v1.79.3 // indirect
 	google.golang.org/protobuf v1.36.11 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 )
 
 require (
 	github.com/aymanbagabas/go-osc52/v2 v2.0.1 // indirect
-	github.com/charmbracelet/glamour v0.10.0
-	github.com/charmbracelet/x/ansi v0.11.6 // indirect
+	github.com/charmbracelet/glamour v1.0.0
+	github.com/charmbracelet/x/ansi v0.11.6
 	github.com/charmbracelet/x/term v0.2.2 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/lucasb-eyer/go-colorful v1.3.0 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
-	github.com/mattn/go-runewidth v0.0.20 // indirect
+	github.com/mattn/go-runewidth v0.0.21 // indirect
 	github.com/muesli/cancelreader v0.2.2 // indirect
 	github.com/muesli/termenv v0.16.0 // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
 	github.com/spf13/pflag v1.0.10 // indirect
-	golang.org/x/sync v0.19.0 // indirect
-	golang.org/x/sys v0.41.0 // indirect
-	golang.org/x/text v0.34.0 // indirect
+	golang.org/x/sync v0.20.0 // indirect
+	golang.org/x/sys v0.42.0 // indirect
+	golang.org/x/text v0.35.0
 )

go.sum

@@ -1,15 +1,17 @@
 charm.land/bubbles/v2 v2.0.0 h1:tE3eK/pHjmtrDiRdoC9uGNLgpopOd8fjhEe31B/ai5s=
 charm.land/bubbles/v2 v2.0.0/go.mod h1:rCHoleP2XhU8um45NTuOWBPNVHxnkXKTiZqcclL/qOI=
-charm.land/bubbletea/v2 v2.0.0 h1:p0d6CtWyJXJ9GfzMpUUqbP/XUUhhlk06+vCKWmox1wQ=
-charm.land/bubbletea/v2 v2.0.0/go.mod h1:3LRff2U4WIYXy7MTxfbAQ+AdfM3D8Xuvz2wbsOD9OHQ=
-charm.land/fantasy v0.10.0 h1:6PD+1rrsCgLIG1n+PAZp/gHiC0dltU0cvb7c8zUKyu8=
-charm.land/fantasy v0.10.0/go.mod h1:KIeNQUpJTswwpY0P6HJsr3LBFgfTDb8FDpOdVQMsKqY=
-charm.land/lipgloss/v2 v2.0.0 h1:sd8N/B3x892oiOjFfBQdXBQp3cAkvjGaU5TvVZC3ivo=
-charm.land/lipgloss/v2 v2.0.0/go.mod h1:w6SnmsBFBmEFBodiEDurGS/sdUY/u1+v72DqUzc6J14=
+charm.land/bubbletea/v2 v2.0.2 h1:4CRtRnuZOdFDTWSff9r8QFt/9+z6Emubz3aDMnf/dx0=
+charm.land/bubbletea/v2 v2.0.2/go.mod h1:3LRff2U4WIYXy7MTxfbAQ+AdfM3D8Xuvz2wbsOD9OHQ=
+charm.land/fantasy v0.17.1 h1:SQzfnyJPDuQWt6e//KKmQmEEXdqHMC0IZz10XwkLcEM=
+charm.land/fantasy v0.17.1/go.mod h1:FF5ALCCHETacHJPBqU42CtwMInYQ0ul52fdzIHQMbQk=
+charm.land/huh/v2 v2.0.3 h1:2cJsMqEPwSywGHvdlKsJyQKPtSJLVnFKyFbsYZTlLkU=
+charm.land/huh/v2 v2.0.3/go.mod h1:93eEveeeqn47MwiC3tf+2atZ2l7Is88rAtmZNZ8x9Wc=
+charm.land/lipgloss/v2 v2.0.2 h1:xFolbF8JdpNkM2cEPTfXEcW1p6NRzOWTSamRfYEw8cs=
+charm.land/lipgloss/v2 v2.0.2/go.mod h1:KjPle2Qd3YmvP1KL5OMHiHysGcNwq6u83MUjYkFvEkM=
 cloud.google.com/go v0.123.0 h1:2NAUJwPR47q+E35uaJeYoNhuNEM9kM8SjgRgdeOJUSE=
 cloud.google.com/go v0.123.0/go.mod h1:xBoMV08QcqUGuPW65Qfm1o9Y4zKZBpGS+7bImXLTAZU=
-cloud.google.com/go/auth v0.18.2 h1:+Nbt5Ev0xEqxlNjd6c+yYUeosQ5TtEUaNcN/3FozlaM=
-cloud.google.com/go/auth v0.18.2/go.mod h1:xD+oY7gcahcu7G2SG2DsBerfFxgPAJz17zz2joOFF3M=
+cloud.google.com/go/auth v0.19.0 h1:DGYwtbcsGsT1ywuxsIoWi1u/vlks0moIblQHgSDgQkQ=
+cloud.google.com/go/auth v0.19.0/go.mod h1:2Aph7BT2KnaSFOM0JDPyiYgNh6PL9vGMiP8CUIXZ+IY=
 cloud.google.com/go/auth/oauth2adapt v0.2.8 h1:keo8NaayQZ6wimpNSmW5OPc283g65QNIiLpZnkHRbnc=
 cloud.google.com/go/auth/oauth2adapt v0.2.8/go.mod h1:XQ9y31RkqZCcwJWNSx2Xvric3RrU88hAYYbjDWYDL+c=
 cloud.google.com/go/compute/metadata v0.9.0 h1:pDUj4QMoPejqq20dK0Pg2N4yG9zIkYGdBtwLoEkH9Zs=
@@ -32,74 +34,82 @@ github.com/alecthomas/repr v0.5.2 h1:SU73FTI9D1P5UNtvseffFSGmdNci/O6RsqzeXJtP0Qs
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-github.com/aws/aws-sdk-go-v2 v1.41.2/go.mod h1:IvvlAZQXvTXznUPfRVfryiG1fbzE2NGK6m9u39YQ+S4=
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+github.com/mattn/go-runewidth v0.0.21/go.mod h1:XBkDxAl56ILZc9knddidhrOlY5R/pDhgLpndooCuJAs=
 github.com/microcosm-cc/bluemonday v1.0.27 h1:MpEUotklkwCSLeH+Qdx1VJgNqLlpY2KXwXFM08ygZfk=
 github.com/microcosm-cc/bluemonday v1.0.27/go.mod h1:jFi9vgW+H7c3V0lb6nR74Ib/DIB5OBs92Dimizgw2cA=
+github.com/mitchellh/hashstructure/v2 v2.0.2 h1:vGKWl0YJqUNxE8d+h8f6NJLcCJrgbhC4NcD46KavDd4=
+github.com/mitchellh/hashstructure/v2 v2.0.2/go.mod h1:MG3aRVU/N29oo/V/IhBX8GR/zz4kQkprJgF2EVszyDE=
 github.com/muesli/cancelreader v0.2.2 h1:3I4Kt4BQjOR54NavqnDogx/MIoWBFa0StPA8ELUXHmA=
 github.com/muesli/cancelreader v0.2.2/go.mod h1:3XuTXfFS2VjM+HTLZY9Ak0l6eUKfijIfMUZ4EgX0QYo=
 github.com/muesli/mango v0.2.0 h1:iNNc0c5VLQ6fsMgAqGQofByNUBH2Q2nEbD6TaI+5yyQ=
@@ -210,10 +228,8 @@ github.com/muesli/roff v0.1.0 h1:YD0lalCotmYuF5HhZliKWlIx7IEhiXeSfq7hNjFqGF8=
 github.com/muesli/roff v0.1.0/go.mod h1:pjAHQM9hdUUwm/krAfrLGgJkXJ+YuhtsfZ42kieB2Ig=
 github.com/muesli/termenv v0.16.0 h1:S5AlUN9dENB57rsbnkPyfdGuWIlkmzJjbFf0Tf5FWUc=
 github.com/muesli/termenv v0.16.0/go.mod h1:ZRfOIKPFDYQoDFF4Olj7/QJbW60Ol/kL1pU3VfY/Cnk=
-github.com/openai/openai-go/v2 v2.7.1 h1:/tfvTJhfv7hTSL8mWwc5VL4WLLSDL5yn9VqVykdu9r8=
-github.com/openai/openai-go/v2 v2.7.1/go.mod h1:jrJs23apqJKKbT+pqtFgNKpRju/KP9zpUTZhz3GElQE=
-github.com/pelletier/go-toml/v2 v2.2.4 h1:mye9XuhQ6gvn5h28+VilKrrPoQVanw5PMw/TB0t5Ec4=
-github.com/pelletier/go-toml/v2 v2.2.4/go.mod h1:2gIqNv+qfxSVS7cM2xJQKtLSTLUE9V8t9Stt+h56mCY=
+github.com/pelletier/go-toml/v2 v2.3.0 h1:k59bC/lIZREW0/iVaQR8nDHxVq8OVlIzYCOJf421CaM=
+github.com/pelletier/go-toml/v2 v2.3.0/go.mod h1:2gIqNv+qfxSVS7cM2xJQKtLSTLUE9V8t9Stt+h56mCY=
 github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c h1:+mdjkGKdHQG3305AYmdv1U2eRNDiU2ErMBj1gwrq8eQ=
 github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c/go.mod h1:7rwL4CYBLnjLxUqIJNnCWiEdr3bn6IUYi15bNlnbCCU=
 github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10 h1:GFCKgmp0tecUJ0sJuv4pzYCqS9+RGSn52M3FUwPs+uo=
@@ -257,63 +273,65 @@ github.com/tidwall/sjson v1.2.5 h1:kLy8mja+1c9jlljvWTlSazM7cKDRfJuR/bOJhcY5NcY=
 github.com/tidwall/sjson v1.2.5/go.mod h1:Fvgq9kS/6ociJEDnK0Fk1cpYF4FIW6ZF7LAe+6jwd28=
 github.com/traefik/yaegi v0.16.1 h1:f1De3DVJqIDKmnasUF6MwmWv1dSEEat0wcpXhD2On3E=
 github.com/traefik/yaegi v0.16.1/go.mod h1:4eVhbPb3LnD2VigQjhYbEJ69vDRFdT2HQNrXx8eEwUY=
-github.com/wk8/go-ordered-map/v2 v2.1.8 h1:5h/BUHu93oj4gIdvHHHGsScSTMijfx5PeYkE/fJgbpc=
-github.com/wk8/go-ordered-map/v2 v2.1.8/go.mod h1:5nJHM5DyteebpVlHnWMV0rPz6Zp7+xBAnxjb1X5vnTw=
 github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e h1:JVG44RsyaB9T2KIHavMF/ppJZNG9ZpyihvCd0w101no=
 github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e/go.mod h1:RbqR21r5mrJuqunuUZ/Dhy/avygyECGrLceyNeo4LiM=
 github.com/yosida95/uritemplate/v3 v3.0.2 h1:Ed3Oyj9yrmi9087+NczuL5BwkIc4wvTb5zIM+UJPGz4=
 github.com/yosida95/uritemplate/v3 v3.0.2/go.mod h1:ILOh0sOhIJR3+L/8afwt/kE++YT040gmv5BQTMR2HP4=
-github.com/yuin/goldmark v1.7.16 h1:n+CJdUxaFMiDUNnWC3dMWCIQJSkxH4uz3ZwQBkAlVNE=
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internal/acpserver/agent.go

@@ -0,0 +1,260 @@
+// Package acpserver implements a Kit-backed ACP (Agent Client Protocol) agent.
+//
+// It bridges Kit's LLM execution, tool system, and session management to the
+// ACP protocol over stdio, allowing ACP clients (such as OpenCode) to drive
+// Kit as a remote coding agent.
+package acpserver
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"sync/atomic"
+
+	"github.com/charmbracelet/log"
+	acp "github.com/coder/acp-go-sdk"
+
+	kit "github.com/mark3labs/kit/pkg/kit"
+)
+
+// Version is injected at build time; fallback to "dev".
+var Version = "dev"
+
+// Agent implements the acp.Agent interface, delegating to Kit for LLM
+// execution, tool calls, and session management.
+type Agent struct {
+	conn     *acp.AgentSideConnection
+	registry *sessionRegistry
+
+	// toolCallCounter provides unique IDs for tool calls within a turn.
+	toolCallCounter atomic.Int64
+}
+
+// NewAgent creates a new ACP agent backed by Kit.
+func NewAgent() *Agent {
+	return &Agent{
+		registry: newSessionRegistry(),
+	}
+}
+
+// SetAgentConnection stores the connection so the agent can send session
+// updates (streaming, tool calls, etc.) back to the ACP client. This follows
+// the AgentConnAware duck-typing pattern from the SDK.
+func (a *Agent) SetAgentConnection(conn *acp.AgentSideConnection) {
+	a.conn = conn
+}
+
+// Close shuts down all active sessions.
+func (a *Agent) Close() {
+	a.registry.closeAll()
+}
+
+// ---------------------------------------------------------------------------
+// acp.Agent interface implementation
+// ---------------------------------------------------------------------------
+
+// Authenticate handles authentication requests. Kit doesn't require auth for
+// local stdio usage, so this is a no-op.
+func (a *Agent) Authenticate(_ context.Context, _ acp.AuthenticateRequest) (acp.AuthenticateResponse, error) {
+	return acp.AuthenticateResponse{}, nil
+}
+
+// Initialize negotiates capabilities with the ACP client.
+func (a *Agent) Initialize(_ context.Context, params acp.InitializeRequest) (acp.InitializeResponse, error) {
+	log.Debug("acp: initialize", "protocol_version", params.ProtocolVersion)
+
+	return acp.InitializeResponse{
+		ProtocolVersion: acp.ProtocolVersion(1),
+		AgentCapabilities: acp.AgentCapabilities{
+			LoadSession: true,
+			PromptCapabilities: acp.PromptCapabilities{
+				EmbeddedContext: true,
+				Image:           true,
+			},
+		},
+		AgentInfo: &acp.Implementation{
+			Name:    "Kit",
+			Version: Version,
+		},
+	}, nil
+}
+
+// NewSession creates a new Kit session for the given working directory.
+func (a *Agent) NewSession(ctx context.Context, params acp.NewSessionRequest) (acp.NewSessionResponse, error) {
+	cwd := params.Cwd
+	if cwd == "" {
+		return acp.NewSessionResponse{}, acp.NewInvalidParams("cwd is required")
+	}
+
+	log.Debug("acp: new_session", "cwd", cwd)
+
+	sess, err := a.registry.create(ctx, cwd)
+	if err != nil {
+		log.Error("acp: session creation failed", "cwd", cwd, "error", err)
+		return acp.NewSessionResponse{}, fmt.Errorf("create session: %w", err)
+	}
+
+	return acp.NewSessionResponse{
+		SessionId: acp.SessionId(sess.sessionID),
+	}, nil
+}
+
+// Prompt handles the main agent execution. It subscribes to Kit's event bus,
+// converts events to ACP session updates, and runs the prompt through Kit's
+// full turn lifecycle (hooks, LLM, tool calls, persistence).
+func (a *Agent) Prompt(ctx context.Context, params acp.PromptRequest) (acp.PromptResponse, error) {
+	sessionID := string(params.SessionId)
+	sess, ok := a.registry.get(sessionID)
+	if !ok {
+		return acp.PromptResponse{}, acp.NewInvalidParams(
+			fmt.Sprintf("session not found: %s", sessionID),
+		)
+	}
+
+	// Extract text from prompt content blocks.
+	promptText := extractPromptText(params.Prompt)
+	if promptText == "" {
+		return acp.PromptResponse{}, acp.NewInvalidParams("empty prompt")
+	}
+
+	log.Debug("acp: prompt", "session", sessionID, "prompt_len", len(promptText))
+
+	// Create a cancellable context for this prompt turn.
+	promptCtx, cancel := context.WithCancel(ctx)
+	sess.setCancel(cancel)
+	defer sess.clearCancel()
+
+	// Subscribe to Kit events and stream them as ACP session updates.
+	unsub := a.subscribeEvents(promptCtx, sess.kit, params.SessionId)
+	defer unsub()
+
+	// Run the prompt through Kit's full turn lifecycle.
+	_, err := sess.kit.PromptResult(promptCtx, promptText)
+	if err != nil {
+		if promptCtx.Err() != nil {
+			return acp.PromptResponse{
+				StopReason: acp.StopReasonCancelled,
+			}, nil
+		}
+		return acp.PromptResponse{}, fmt.Errorf("prompt failed: %w", err)
+	}
+
+	return acp.PromptResponse{
+		StopReason: acp.StopReasonEndTurn,
+	}, nil
+}
+
+// Cancel cancels the ongoing prompt for a session.
+func (a *Agent) Cancel(_ context.Context, params acp.CancelNotification) error {
+	sessionID := string(params.SessionId)
+	sess, ok := a.registry.get(sessionID)
+	if !ok {
+		return nil // No-op if session doesn't exist.
+	}
+
+	log.Debug("acp: cancel", "session", sessionID)
+	sess.cancelPrompt()
+	return nil
+}
+
+// SetSessionMode is a no-op for now — Kit doesn't have built-in session modes.
+func (a *Agent) SetSessionMode(_ context.Context, _ acp.SetSessionModeRequest) (acp.SetSessionModeResponse, error) {
+	return acp.SetSessionModeResponse{}, nil
+}
+
+// ---------------------------------------------------------------------------
+// Event streaming: Kit events → ACP SessionUpdate notifications
+// ---------------------------------------------------------------------------
+
+// subscribeEvents subscribes to Kit's event bus and forwards events as ACP
+// session update notifications to the client.
+func (a *Agent) subscribeEvents(ctx context.Context, k *kit.Kit, sessionID acp.SessionId) func() {
+	return k.Subscribe(func(e kit.Event) {
+		// Don't send updates after the context is cancelled.
+		if ctx.Err() != nil {
+			return
+		}
+
+		var update *acp.SessionUpdate
+		switch ev := e.(type) {
+		case kit.MessageUpdateEvent:
+			u := acp.UpdateAgentMessageText(ev.Chunk)
+			update = &u
+
+		case kit.ReasoningDeltaEvent:
+			u := acp.UpdateAgentThoughtText(ev.Delta)
+			update = &u
+
+		case kit.ToolCallEvent:
+			tcID := acp.ToolCallId(ev.ToolCallID)
+			if tcID == "" {
+				tcID = acp.ToolCallId(fmt.Sprintf("tc_%d", a.toolCallCounter.Add(1)))
+			}
+			u := acp.StartToolCall(tcID, ev.ToolName,
+				acp.WithStartStatus(acp.ToolCallStatusInProgress),
+				acp.WithStartRawInput(parseToolArgs(ev.ToolArgs)),
+			)
+			update = &u
+
+		case kit.ToolResultEvent:
+			tcID := acp.ToolCallId(ev.ToolCallID)
+			if tcID == "" {
+				tcID = acp.ToolCallId(fmt.Sprintf("tc_%d", a.toolCallCounter.Load()))
+			}
+			status := acp.ToolCallStatusCompleted
+			if ev.IsError {
+				status = acp.ToolCallStatusFailed
+			}
+			u := acp.UpdateToolCall(tcID,
+				acp.WithUpdateStatus(status),
+				acp.WithUpdateContent([]acp.ToolCallContent{
+					acp.ToolContent(acp.TextBlock(ev.Result)),
+				}),
+			)
+			update = &u
+
+		case kit.ToolCallContentEvent:
+			u := acp.UpdateAgentMessageText(ev.Content)
+			update = &u
+		}
+
+		if update != nil {
+			_ = a.conn.SessionUpdate(ctx, acp.SessionNotification{
+				SessionId: sessionID,
+				Update:    *update,
+			})
+		}
+	})
+}
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+// extractPromptText extracts the concatenated text content from ACP content
+// blocks. Non-text blocks are ignored for now.
+func extractPromptText(blocks []acp.ContentBlock) string {
+	var text string
+	for _, block := range blocks {
+		if block.Text != nil {
+			if text != "" {
+				text += "\n"
+			}
+			text += block.Text.Text
+		}
+	}
+	return text
+}
+
+// parseToolArgs attempts to parse a JSON tool args string into a map for
+// structured display. Falls back to a simple string wrapper.
+func parseToolArgs(args string) any {
+	if args == "" {
+		return nil
+	}
+	var m map[string]any
+	if err := json.Unmarshal([]byte(args), &m); err == nil {
+		return m
+	}
+	return map[string]any{"input": args}
+}

internal/acpserver/session.go

@@ -0,0 +1,294 @@
+package acpserver
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"sync"
+
+	"github.com/charmbracelet/log"
+
+	"github.com/mark3labs/kit/internal/extensions"
+	kit "github.com/mark3labs/kit/pkg/kit"
+)
+
+// acpSession maps an ACP session to a Kit instance with its own tree session.
+type acpSession struct {
+	kit       *kit.Kit
+	cancelFn  context.CancelFunc // cancels the current prompt
+	cancelMu  sync.Mutex
+	cwd       string
+	sessionID string // Kit-generated session ID (from JSONL header)
+}
+
+// sessionRegistry is a thread-safe registry of ACP session ID → Kit sessions.
+type sessionRegistry struct {
+	mu       sync.RWMutex
+	sessions map[string]*acpSession // ACP session ID → session
+}
+
+func newSessionRegistry() *sessionRegistry {
+	return &sessionRegistry{
+		sessions: make(map[string]*acpSession),
+	}
+}
+
+// create creates a new Kit instance with a persisted tree session for the
+// given working directory. The Kit-generated session ID is used as the ACP
+// session ID so the mapping is 1:1.
+func (r *sessionRegistry) create(ctx context.Context, cwd string) (*acpSession, error) {
+	kitInstance, err := kit.New(ctx, &kit.Options{
+		SessionDir: cwd,
+		Quiet:      true,
+		Streaming:  true,
+	})
+	if err != nil {
+		// Provide actionable guidance for provider auth errors, which are
+		// the most common failure mode when running via ACP.
+		msg := err.Error()
+		if strings.Contains(msg, "API key") || strings.Contains(msg, "credentials") || strings.Contains(msg, "OAuth") {
+			return nil, fmt.Errorf("provider authentication failed: %w — run 'kit auth login <provider>' or set the appropriate environment variable before starting 'kit acp'", err)
+		}
+		return nil, fmt.Errorf("create kit instance: %w", err)
+	}
+
+	sessionID := kitInstance.GetSessionID()
+	if sessionID == "" {
+		_ = kitInstance.Close()
+		return nil, fmt.Errorf("kit instance has no session ID")
+	}
+
+	// Wire extension context with headless implementations so extensions
+	// work in ACP mode. TUI-dependent features (widgets, prompts, editor)
+	// become no-ops or return cancelled; all data/model/tool APIs work
+	// identically to interactive mode.
+	if kitInstance.HasExtensions() {
+		kitInstance.SetExtensionContext(extensions.Context{
+			SessionID:   sessionID,
+			CWD:         cwd,
+			Model:       kitInstance.GetModelString(),
+			Interactive: false,
+
+			// Output — route through structured logger.
+			Print:      func(text string) { log.Debug("extension: print", "text", text) },
+			PrintInfo:  func(text string) { log.Info("extension: info", "text", text) },
+			PrintError: func(text string) { log.Error("extension: error", "text", text) },
+			PrintBlock: func(opts extensions.PrintBlockOpts) {
+				log.Info("extension: block", "subtitle", opts.Subtitle, "text", opts.Text)
+			},
+
+			// Message injection — no-ops for now; ACP clients drive prompts.
+			SendMessage:   func(string) {},
+			CancelAndSend: func(string) {},
+			Exit:          func() {},
+
+			// TUI widgets/chrome — silent no-ops (no TUI in ACP).
+			SetWidget:       func(extensions.WidgetConfig) {},
+			RemoveWidget:    func(string) {},
+			SetHeader:       func(extensions.HeaderFooterConfig) {},
+			RemoveHeader:    func() {},
+			SetFooter:       func(extensions.HeaderFooterConfig) {},
+			RemoveFooter:    func() {},
+			SetEditor:       func(extensions.EditorConfig) {},
+			ResetEditor:     func() {},
+			SetEditorText:   func(string) {},
+			SetUIVisibility: func(extensions.UIVisibility) {},
+			SetStatus:       func(string, string, int) {},
+			RemoveStatus:    func(string) {},
+
+			// Interactive prompts — return cancelled (no user to prompt).
+			PromptSelect: func(extensions.PromptSelectConfig) extensions.PromptSelectResult {
+				return extensions.PromptSelectResult{Cancelled: true}
+			},
+			PromptConfirm: func(extensions.PromptConfirmConfig) extensions.PromptConfirmResult {
+				return extensions.PromptConfirmResult{Cancelled: true}
+			},
+			PromptInput: func(extensions.PromptInputConfig) extensions.PromptInputResult {
+				return extensions.PromptInputResult{Cancelled: true}
+			},
+			ShowOverlay: func(extensions.OverlayConfig) extensions.OverlayResult {
+				return extensions.OverlayResult{Cancelled: true, Index: -1}
+			},
+			SuspendTUI: func(callback func()) error { callback(); return nil },
+
+			// Data access — delegate to Kit instance.
+			GetContextStats: func() extensions.ContextStats {
+				s := kitInstance.GetContextStats()
+				return extensions.ContextStats{
+					EstimatedTokens: s.EstimatedTokens,
+					ContextLimit:    s.ContextLimit,
+					UsagePercent:    s.UsagePercent,
+					MessageCount:    s.MessageCount,
+				}
+			},
+			GetMessages:    func() []extensions.SessionMessage { return kitInstance.GetSessionMessages() },
+			GetSessionPath: func() string { return kitInstance.GetSessionFilePath() },
+			AppendEntry: func(entryType, data string) (string, error) {
+				return kitInstance.AppendExtensionEntry(entryType, data)
+			},
+			GetEntries: func(entryType string) []extensions.ExtensionEntry {
+				return kitInstance.GetExtensionEntries(entryType)
+			},
+
+			// Options, model, and tool management.
+			GetOption: func(name string) string { return kitInstance.GetExtensionOption(name) },
+			SetOption: func(name, value string) { kitInstance.SetExtensionOption(name, value) },
+			SetModel: func(modelString string) error {
+				previousModel := kitInstance.GetExtensionContext().Model
+				if err := kitInstance.SetModel(context.Background(), modelString); err != nil {
+					return err
+				}
+				kitInstance.UpdateExtensionContextModel(modelString)
+				kitInstance.EmitModelChange(modelString, previousModel, "extension")
+				return nil
+			},
+			GetAvailableModels: func() []extensions.ModelInfoEntry { return kitInstance.GetAvailableModels() },
+			EmitCustomEvent:    func(name, data string) { kitInstance.EmitExtensionCustomEvent(name, data) },
+			GetAllTools:        func() []extensions.ToolInfo { return kitInstance.GetExtensionToolInfos() },
+			SetActiveTools:     func(names []string) { kitInstance.SetExtensionActiveTools(names) },
+
+			// LLM completions and subagents.
+			Complete: func(req extensions.CompleteRequest) (extensions.CompleteResponse, error) {
+				return kitInstance.ExecuteCompletion(context.Background(), req)
+			},
+			SpawnSubagent: func(config extensions.SubagentConfig) (*extensions.SubagentHandle, *extensions.SubagentResult, error) {
+				sdkCfg := kit.SubagentConfig{
+					Prompt:       config.Prompt,
+					Model:        config.Model,
+					SystemPrompt: config.SystemPrompt,
+					Timeout:      config.Timeout,
+					NoSession:    config.NoSession,
+				}
+				if config.OnEvent != nil {
+					sdkCfg.OnEvent = func(e kit.Event) {
+						se := sdkEventToSubagentEvent(e)
+						if se.Type != "" {
+							config.OnEvent(se)
+						}
+					}
+				}
+				result, err := kitInstance.Subagent(context.Background(), sdkCfg)
+				if result == nil {
+					return nil, &extensions.SubagentResult{Error: err}, err
+				}
+				extResult := &extensions.SubagentResult{
+					Response:  result.Response,
+					Error:     result.Error,
+					SessionID: result.SessionID,
+					Elapsed:   result.Elapsed,
+				}
+				if result.Usage != nil {
+					extResult.Usage = &extensions.SubagentUsage{
+						InputTokens:  result.Usage.InputTokens,
+						OutputTokens: result.Usage.OutputTokens,
+					}
+				}
+				return nil, extResult, err
+			},
+
+			// Render — fall back to logging.
+			RenderMessage: func(name, content string) {
+				renderer := kitInstance.GetExtensionMessageRenderer(name)
+				if renderer != nil && renderer.Render != nil {
+					content = renderer.Render(content, 80)
+				}
+				log.Info("extension: message", "renderer", name, "content", content)
+			},
+			ReloadExtensions: func() error { return kitInstance.ReloadExtensions() },
+		})
+		kitInstance.EmitSessionStart()
+	}
+
+	sess := &acpSession{
+		kit:       kitInstance,
+		cwd:       cwd,
+		sessionID: sessionID,
+	}
+
+	r.mu.Lock()
+	r.sessions[sessionID] = sess
+	r.mu.Unlock()
+
+	return sess, nil
+}
+
+// get retrieves a session by ACP session ID.
+func (r *sessionRegistry) get(sessionID string) (*acpSession, bool) {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	s, ok := r.sessions[sessionID]
+	return s, ok
+}
+
+// closeAll closes all sessions.
+func (r *sessionRegistry) closeAll() {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	for id, sess := range r.sessions {
+		if sess.kit != nil {
+			_ = sess.kit.Close()
+		}
+		delete(r.sessions, id)
+	}
+}
+
+// cancelPrompt cancels the current prompt for a session, if any.
+func (s *acpSession) cancelPrompt() {
+	s.cancelMu.Lock()
+	defer s.cancelMu.Unlock()
+	if s.cancelFn != nil {
+		s.cancelFn()
+		s.cancelFn = nil
+	}
+}
+
+// setCancel stores a cancel function for the current prompt.
+func (s *acpSession) setCancel(cancel context.CancelFunc) {
+	s.cancelMu.Lock()
+	defer s.cancelMu.Unlock()
+	s.cancelFn = cancel
+}
+
+// clearCancel clears the stored cancel function (called when prompt completes).
+func (s *acpSession) clearCancel() {
+	s.cancelMu.Lock()
+	defer s.cancelMu.Unlock()
+	s.cancelFn = nil
+}
+
+// sdkEventToSubagentEvent converts an SDK event to an extension SubagentEvent.
+func sdkEventToSubagentEvent(e kit.Event) extensions.SubagentEvent {
+	switch ev := e.(type) {
+	case kit.MessageUpdateEvent:
+		return extensions.SubagentEvent{Type: "text", Content: ev.Chunk}
+	case kit.ReasoningDeltaEvent:
+		return extensions.SubagentEvent{Type: "reasoning", Content: ev.Delta}
+	case kit.ToolCallEvent:
+		return extensions.SubagentEvent{
+			Type: "tool_call", ToolCallID: ev.ToolCallID,
+			ToolName: ev.ToolName, ToolKind: ev.ToolKind, ToolArgs: ev.ToolArgs,
+		}
+	case kit.ToolExecutionStartEvent:
+		return extensions.SubagentEvent{
+			Type: "tool_execution_start", ToolCallID: ev.ToolCallID,
+			ToolName: ev.ToolName, ToolKind: ev.ToolKind,
+		}
+	case kit.ToolExecutionEndEvent:
+		return extensions.SubagentEvent{
+			Type: "tool_execution_end", ToolCallID: ev.ToolCallID,
+			ToolName: ev.ToolName, ToolKind: ev.ToolKind,
+		}
+	case kit.ToolResultEvent:
+		return extensions.SubagentEvent{
+			Type: "tool_result", ToolCallID: ev.ToolCallID,
+			ToolName: ev.ToolName, ToolKind: ev.ToolKind,
+			ToolResult: ev.Result, IsError: ev.IsError,
+		}
+	case kit.TurnStartEvent:
+		return extensions.SubagentEvent{Type: "turn_start"}
+	case kit.TurnEndEvent:
+		return extensions.SubagentEvent{Type: "turn_end"}
+	default:
+		return extensions.SubagentEvent{}
+	}
+}

internal/agent/agent.go

@@ -41,13 +41,15 @@ type AgentConfig struct {
 }
 
 // ToolCallHandler is a function type for handling tool calls as they happen.
-type ToolCallHandler func(toolName, toolArgs string)
+type ToolCallHandler func(toolCallID, toolName, toolArgs string)
 
 // ToolExecutionHandler is a function type for handling tool execution start/end events.
-type ToolExecutionHandler func(toolName string, isStarting bool)
+type ToolExecutionHandler func(toolCallID, toolName, toolArgs string, isStarting bool)
 
 // ToolResultHandler is a function type for handling tool results.
-type ToolResultHandler func(toolName, toolArgs, result string, isError bool)
+// The metadata parameter carries optional structured data (e.g. file diff
+// info) from the tool execution, JSON-encoded. It may be empty.
+type ToolResultHandler func(toolCallID, toolName, toolArgs, result, metadata string, isError bool)
 
 // ResponseHandler is a function type for handling LLM responses.
 type ResponseHandler func(content string)
@@ -58,6 +60,21 @@ type StreamingResponseHandler func(content string)
 // ToolCallContentHandler is a function type for handling content that accompanies tool calls.
 type ToolCallContentHandler func(content string)
 
+// ReasoningDeltaHandler is a function type for handling streaming reasoning/thinking deltas.
+type ReasoningDeltaHandler func(delta string)
+
+// ToolOutputHandler is a function type for handling streaming tool output chunks.
+// Used by tools like bash to stream output as it arrives rather than waiting
+// for the command to complete. The isStderr flag indicates if the chunk
+// contains stderr output.
+// Note: This is an alias for core.ToolOutputCallback to avoid import cycles.
+type ToolOutputHandler = core.ToolOutputCallback
+
+// StepUsageHandler is a function type for handling token usage after each
+// complete step in a multi-step agent turn. This enables real-time cost
+// tracking during long-running tool-calling conversations.
+type StepUsageHandler func(inputTokens, outputTokens, cacheReadTokens, cacheCreationTokens int64)
+
 // Agent represents an AI agent with core tool integration using the fantasy library.
 // Core tools (bash, read, write, edit, grep, find, ls) are registered as direct
 // fantasy.AgentTool implementations — no MCP layer, no serialization overhead.
@@ -74,6 +91,7 @@ type Agent struct {
 	streamingEnabled bool
 	coreTools        []fantasy.AgentTool
 	extraTools       []fantasy.AgentTool
+	toolWrapper      func([]fantasy.AgentTool) []fantasy.AgentTool // stored for SetModel rebuild
 }
 
 // GenerateWithLoopResult contains the result and conversation history from an agent interaction.
@@ -86,6 +104,8 @@ type GenerateWithLoopResult struct {
 	Messages []message.Message
 	// TotalUsage contains aggregate token usage across all steps
 	TotalUsage fantasy.Usage
+	// StopReason is the LLM provider's finish reason for the final response.
+	StopReason string
 }
 
 // NewAgent creates a new Agent with core tools and optional MCP tool integration.
@@ -156,6 +176,28 @@ func NewAgent(ctx context.Context, agentConfig *AgentConfig) (*Agent, error) {
 		))
 	}
 
+	// Pass provider-specific options (e.g. OpenAI Responses API reasoning settings).
+	if providerResult.ProviderOptions != nil {
+		agentOpts = append(agentOpts, fantasy.WithProviderOptions(providerResult.ProviderOptions))
+	}
+
+	// Pass generation parameters when available.
+	if agentConfig.ModelConfig != nil {
+		// Skip max_output_tokens for providers that don't support it (e.g., Codex OAuth)
+		if agentConfig.ModelConfig.MaxTokens > 0 && !providerResult.SkipMaxOutputTokens {
+			agentOpts = append(agentOpts, fantasy.WithMaxOutputTokens(int64(agentConfig.ModelConfig.MaxTokens)))
+		}
+		if agentConfig.ModelConfig.Temperature != nil {
+			agentOpts = append(agentOpts, fantasy.WithTemperature(float64(*agentConfig.ModelConfig.Temperature)))
+		}
+		if agentConfig.ModelConfig.TopP != nil {
+			agentOpts = append(agentOpts, fantasy.WithTopP(float64(*agentConfig.ModelConfig.TopP)))
+		}
+		if agentConfig.ModelConfig.TopK != nil {
+			agentOpts = append(agentOpts, fantasy.WithTopK(int64(*agentConfig.ModelConfig.TopK)))
+		}
+	}
+
 	// Create the fantasy agent
 	fantasyAgent := fantasy.NewAgent(providerResult.Model, agentOpts...)
 
@@ -179,6 +221,7 @@ func NewAgent(ctx context.Context, agentConfig *AgentConfig) (*Agent, error) {
 		streamingEnabled: agentConfig.StreamingEnabled,
 		coreTools:        coreTools,
 		extraTools:       agentConfig.ExtraTools,
+		toolWrapper:      agentConfig.ToolWrapper,
 	}, nil
 }
 
@@ -188,7 +231,7 @@ func (a *Agent) GenerateWithLoop(ctx context.Context, messages []fantasy.Message
 	onResponse ResponseHandler, onToolCallContent ToolCallContentHandler,
 ) (*GenerateWithLoopResult, error) {
 	return a.GenerateWithLoopAndStreaming(ctx, messages, onToolCall, onToolExecution, onToolResult,
-		onResponse, onToolCallContent, nil)
+		onResponse, onToolCallContent, nil, nil, nil, nil)
 }
 
 // GenerateWithLoopAndStreaming processes messages using the fantasy agent with streaming and callbacks.
@@ -198,11 +241,21 @@ func (a *Agent) GenerateWithLoopAndStreaming(ctx context.Context, messages []fan
 	onToolCall ToolCallHandler, onToolExecution ToolExecutionHandler, onToolResult ToolResultHandler,
 	onResponse ResponseHandler, onToolCallContent ToolCallContentHandler,
 	onStreamingResponse StreamingResponseHandler,
+	onReasoningDelta ReasoningDeltaHandler,
+	onToolOutput ToolOutputHandler,
+	onStepUsage StepUsageHandler,
 ) (*GenerateWithLoopResult, error) {
 
+	// Inject tool output handler into context for use by core tools (e.g., bash).
+	if onToolOutput != nil {
+		ctx = core.ContextWithToolOutputCallback(ctx, onToolOutput)
+	}
+
 	// Fantasy requires the current user input as Prompt, with prior messages as history.
-	// Extract the last user message text as the prompt, and pass everything before it as Messages.
-	prompt, history := splitPromptAndHistory(messages)
+	// Extract the last user message text and files as the prompt, and pass everything
+	// before it as Messages. Files (e.g. clipboard images) are passed via the Files
+	// field so Fantasy includes them in the API request.
+	prompt, files, history := splitPromptAndHistory(messages)
 
 	// Track current tool call info for callbacks
 	var currentToolName string
@@ -213,14 +266,32 @@ func (a *Agent) GenerateWithLoopAndStreaming(ctx context.Context, messages []fan
 	// Stream is required to observe tool execution in real time. The non-streaming
 	// Generate path is reserved for the simple case with no callbacks at all.
 	hasCallbacks := onToolCall != nil || onToolExecution != nil || onToolResult != nil ||
-		onToolCallContent != nil || onStreamingResponse != nil
+		onToolCallContent != nil || onStreamingResponse != nil || onReasoningDelta != nil
 
 	if a.streamingEnabled || hasCallbacks {
+		// Track completed step messages so we can return partial results
+		// on cancellation. Fantasy's Stream() discards accumulated steps
+		// when it returns an error, but the OnStepFinish callback fires
+		// for every step that completed before the error occurred.
+		var completedStepMessages []fantasy.Message
+
 		// Use fantasy's streaming agent
-		result, err := a.fantasyAgent.Stream(ctx, fantasy.AgentStreamCall{
+		streamCall := fantasy.AgentStreamCall{
 			Prompt:   prompt,
+			Files:    files,
 			Messages: history,
 
+			// Reasoning/thinking streaming callback
+			OnReasoningDelta: func(id, delta string) error {
+				if ctx.Err() != nil {
+					return ctx.Err()
+				}
+				if onReasoningDelta != nil {
+					onReasoningDelta(delta)
+				}
+				return nil
+			},
+
 			// Text streaming callback
 			OnTextDelta: func(id, text string) error {
 				if ctx.Err() != nil {
@@ -242,12 +313,12 @@ func (a *Agent) GenerateWithLoopAndStreaming(ctx context.Context, messages []fan
 
 				// Notify about the tool call
 				if onToolCall != nil {
-					onToolCall(tc.ToolName, tc.Input)
+					onToolCall(tc.ToolCallID, tc.ToolName, tc.Input)
 				}
 
 				// Notify tool execution starting
 				if onToolExecution != nil {
-					onToolExecution(tc.ToolName, true)
+					onToolExecution(tc.ToolCallID, tc.ToolName, tc.Input, true)
 				}
 
 				return nil
@@ -260,13 +331,13 @@ func (a *Agent) GenerateWithLoopAndStreaming(ctx context.Context, messages []fan
 				}
 				// Notify tool execution finished
 				if onToolExecution != nil {
-					onToolExecution(tr.ToolName, false)
+					onToolExecution(tr.ToolCallID, tr.ToolName, currentToolArgs, false)
 				}
 
 				if onToolResult != nil {
 					// Extract result text and error status
 					resultText, isError := extractToolResultText(tr)
-					onToolResult(tr.ToolName, currentToolArgs, resultText, isError)
+					onToolResult(tr.ToolCallID, tr.ToolName, currentToolArgs, resultText, tr.ClientMetadata, isError)
 				}
 
 				return nil
@@ -274,6 +345,10 @@ func (a *Agent) GenerateWithLoopAndStreaming(ctx context.Context, messages []fan
 
 			// Step callbacks for content that accompanies tool calls
 			OnStepFinish: func(step fantasy.StepResult) error {
+				// Accumulate messages from completed steps so they can be
+				// persisted even if a later step is cancelled.
+				completedStepMessages = append(completedStepMessages, step.Messages...)
+
 				if ctx.Err() != nil {
 					return ctx.Err()
 				}
@@ -283,10 +358,73 @@ func (a *Agent) GenerateWithLoopAndStreaming(ctx context.Context, messages []fan
 				if text != "" && len(toolCalls) > 0 && onToolCallContent != nil {
 					onToolCallContent(text)
 				}
+				// Emit step usage for real-time cost tracking
+				if onStepUsage != nil {
+					onStepUsage(step.Usage.InputTokens, step.Usage.OutputTokens,
+						step.Usage.CacheReadTokens, step.Usage.CacheCreationTokens)
+				}
 				return nil
 			},
-		})
+		}
+
+		// If a steer channel is attached to the context, wire up a
+		// PrepareStep function that drains the channel between steps
+		// and injects pending steer messages as user messages before
+		// the next LLM call. This enables graceful mid-turn steering
+		// without cancelling in-progress tool execution.
+		if steerCh := steerChFromContext(ctx); steerCh != nil {
+			onConsumed := steerConsumedFromContext(ctx)
+			streamCall.PrepareStep = func(
+				stepCtx context.Context,
+				opts fantasy.PrepareStepFunctionOptions,
+			) (context.Context, fantasy.PrepareStepResult, error) {
+				// Drain all pending steer messages (non-blocking).
+				var steered []string
+				for {
+					select {
+					case msg := <-steerCh:
+						steered = append(steered, msg)
+					default:
+						goto done
+					}
+				}
+			done:
+				result := fantasy.PrepareStepResult{
+					Model:    opts.Model,
+					Messages: opts.Messages,
+				}
+				if len(steered) > 0 {
+					// Inject each steer message as a user message so the
+					// LLM sees the redirection on the next step.
+					for _, text := range steered {
+						result.Messages = append(result.Messages,
+							fantasy.NewUserMessage(text))
+					}
+					// Notify that steer messages were consumed.
+					if onConsumed != nil {
+						onConsumed(len(steered))
+					}
+				}
+				return stepCtx, result, nil
+			}
+		}
+
+		result, err := a.fantasyAgent.Stream(ctx, streamCall)
 		if err != nil {
+			// On cancellation (or any error), return a partial result
+			// containing messages from completed steps so the caller can
+			// persist tool calls and results that finished before the
+			// cancellation. The original input messages are included so
+			// the caller sees the full conversation up to the point of
+			// cancellation.
+			if len(completedStepMessages) > 0 {
+				partialMessages := make([]fantasy.Message, 0, len(messages)+len(completedStepMessages))
+				partialMessages = append(partialMessages, messages...)
+				partialMessages = append(partialMessages, completedStepMessages...)
+				return &GenerateWithLoopResult{
+					ConversationMessages: partialMessages,
+				}, err
+			}
 			return nil, err
 		}
 
@@ -302,6 +440,7 @@ func (a *Agent) GenerateWithLoopAndStreaming(ctx context.Context, messages []fan
 	// Non-streaming path with no callbacks — use the simpler Generate call.
 	result, err := a.fantasyAgent.Generate(ctx, fantasy.AgentCall{
 		Prompt:   prompt,
+		Files:    files,
 		Messages: history,
 	})
 	if err != nil {
@@ -322,27 +461,32 @@ func (a *Agent) GenerateWithLoopAndStreaming(ctx context.Context, messages []fan
 // and returns everything before it as conversation history. Fantasy's agent
 // requires the current turn's input as Prompt (string), with prior messages
 // passed separately as Messages (history).
-func splitPromptAndHistory(messages []fantasy.Message) (string, []fantasy.Message) {
+func splitPromptAndHistory(messages []fantasy.Message) (string, []fantasy.FilePart, []fantasy.Message) {
 	if len(messages) == 0 {
-		return "", nil
+		return "", nil, nil
 	}
 
 	// Walk backwards to find the last user message
 	for i := len(messages) - 1; i >= 0; i-- {
 		if messages[i].Role == fantasy.MessageRoleUser {
-			// Extract text from the user message parts
+			// Extract text and file parts from the user message
 			var prompt string
+			var files []fantasy.FilePart
 			for _, part := range messages[i].Content {
-				if tp, ok := part.(fantasy.TextPart); ok {
-					prompt = tp.Text
-					break
+				switch p := part.(type) {
+				case fantasy.TextPart:
+					if prompt == "" {
+						prompt = p.Text
+					}
+				case fantasy.FilePart:
+					files = append(files, p)
 				}
 			}
 			// History is everything except this last user message
 			history := make([]fantasy.Message, 0, len(messages)-1)
 			history = append(history, messages[:i]...)
 			history = append(history, messages[i+1:]...)
-			return prompt, history
+			return prompt, files, history
 		}
 	}
 
@@ -350,11 +494,11 @@ func splitPromptAndHistory(messages []fantasy.Message) (string, []fantasy.Messag
 	last := messages[len(messages)-1]
 	for _, part := range last.Content {
 		if tp, ok := part.(fantasy.TextPart); ok {
-			return tp.Text, messages[:len(messages)-1]
+			return tp.Text, nil, messages[:len(messages)-1]
 		}
 	}
 
-	return "", messages
+	return "", nil, messages
 }
 
 // convertAgentResult converts a fantasy AgentResult to our GenerateWithLoopResult.
@@ -379,6 +523,7 @@ func convertAgentResult(result *fantasy.AgentResult, originalMessages []fantasy.
 		ConversationMessages: allFantasyMessages,
 		Messages:             allMessages,
 		TotalUsage:           result.TotalUsage,
+		StopReason:           string(result.Response.FinishReason),
 	}
 }
 
@@ -455,6 +600,11 @@ func (a *Agent) GetTools() []fantasy.AgentTool {
 	return allTools
 }
 
+// GetCoreToolCount returns the number of core tools.
+func (a *Agent) GetCoreToolCount() int {
+	return len(a.coreTools)
+}
+
 // GetMCPToolCount returns the number of tools loaded from external MCP servers.
 func (a *Agent) GetMCPToolCount() int {
 	if a.toolManager == nil {
@@ -481,6 +631,89 @@ func (a *Agent) GetLoadedServerNames() []string {
 	return a.toolManager.GetLoadedServerNames()
 }
 
+// SetModel swaps the agent's LLM provider to a new model. The existing tools,
+// system prompt, and configuration are preserved. The old provider is closed
+// if it has a closer. Returns the previous model string for notification.
+func (a *Agent) SetModel(ctx context.Context, config *models.ProviderConfig) error {
+	providerResult, err := models.CreateProvider(ctx, config)
+	if err != nil {
+		return fmt.Errorf("failed to create model provider: %v", err)
+	}
+
+	// Rebuild tool list (same as NewAgent).
+	allTools := make([]fantasy.AgentTool, len(a.coreTools))
+	copy(allTools, a.coreTools)
+	if a.toolManager != nil {
+		allTools = append(allTools, a.toolManager.GetTools()...)
+	}
+	if len(a.extraTools) > 0 {
+		allTools = append(allTools, a.extraTools...)
+	}
+	if a.toolWrapper != nil {
+		allTools = a.toolWrapper(allTools)
+	}
+
+	// Rebuild fantasy agent options.
+	var agentOpts []fantasy.AgentOption
+	if a.systemPrompt != "" {
+		agentOpts = append(agentOpts, fantasy.WithSystemPrompt(a.systemPrompt))
+	}
+	if len(allTools) > 0 {
+		agentOpts = append(agentOpts, fantasy.WithTools(allTools...))
+	}
+	if a.maxSteps > 0 {
+		agentOpts = append(agentOpts, fantasy.WithStopConditions(
+			fantasy.StepCountIs(a.maxSteps),
+		))
+	}
+
+	// Pass provider-specific options (e.g. OpenAI Responses API reasoning settings).
+	if providerResult.ProviderOptions != nil {
+		agentOpts = append(agentOpts, fantasy.WithProviderOptions(providerResult.ProviderOptions))
+	}
+
+	// Pass generation parameters when available.
+	// Skip max_output_tokens for providers that don't support it (e.g., Codex OAuth)
+	if config.MaxTokens > 0 && !providerResult.SkipMaxOutputTokens {
+		agentOpts = append(agentOpts, fantasy.WithMaxOutputTokens(int64(config.MaxTokens)))
+	}
+	if config.Temperature != nil {
+		agentOpts = append(agentOpts, fantasy.WithTemperature(float64(*config.Temperature)))
+	}
+	if config.TopP != nil {
+		agentOpts = append(agentOpts, fantasy.WithTopP(float64(*config.TopP)))
+	}
+	if config.TopK != nil {
+		agentOpts = append(agentOpts, fantasy.WithTopK(int64(*config.TopK)))
+	}
+
+	newFantasyAgent := fantasy.NewAgent(providerResult.Model, agentOpts...)
+
+	// Close old provider.
+	if a.providerCloser != nil {
+		_ = a.providerCloser.Close()
+	}
+
+	// Update model info on MCP tool manager.
+	if a.toolManager != nil {
+		a.toolManager.SetModel(providerResult.Model)
+	}
+
+	// Swap fields.
+	a.fantasyAgent = newFantasyAgent
+	a.model = providerResult.Model
+	a.providerCloser = providerResult.Closer
+
+	// Update provider type.
+	if config.ModelString != "" {
+		if p, _, err := models.ParseModelString(config.ModelString); err == nil {
+			a.providerType = p
+		}
+	}
+
+	return nil
+}
+
 // GetModel returns the underlying fantasy LanguageModel.
 func (a *Agent) GetModel() fantasy.LanguageModel {
 	return a.model

internal/agent/steer.go

@@ -0,0 +1,35 @@
+package agent
+
+import "context"
+
+// steerChKey is the context key for the steer channel.
+type steerChKey struct{}
+
+// steerConsumedKey is the context key for the steer-consumed callback.
+type steerConsumedKey struct{}
+
+// ContextWithSteerCh returns a new context with the steer channel attached.
+// The agent's PrepareStep function checks this channel between steps and
+// injects any pending steer messages as user messages before the next LLM call.
+func ContextWithSteerCh(ctx context.Context, ch <-chan string) context.Context {
+	return context.WithValue(ctx, steerChKey{}, ch)
+}
+
+// ContextWithSteerConsumed returns a new context with a callback that fires
+// when steer messages are consumed by PrepareStep. The count argument is the
+// number of messages injected in this batch.
+func ContextWithSteerConsumed(ctx context.Context, fn func(count int)) context.Context {
+	return context.WithValue(ctx, steerConsumedKey{}, fn)
+}
+
+// steerChFromContext extracts the steer channel from the context, or nil.
+func steerChFromContext(ctx context.Context) <-chan string {
+	ch, _ := ctx.Value(steerChKey{}).(<-chan string)
+	return ch
+}
+
+// steerConsumedFromContext extracts the steer-consumed callback, or nil.
+func steerConsumedFromContext(ctx context.Context) func(int) {
+	fn, _ := ctx.Value(steerConsumedKey{}).(func(int))
+	return fn
+}

internal/app/app.go

@@ -3,6 +3,7 @@ package app
 import (
 	"context"
 	"fmt"
+	"os"
 	"sync"
 
 	tea "charm.land/bubbletea/v2"
@@ -13,6 +14,12 @@ import (
 	kit "github.com/mark3labs/kit/pkg/kit"
 )
 
+// queueItem holds a prompt and optional image attachments for the execution queue.
+type queueItem struct {
+	Prompt string
+	Files  []fantasy.FilePart
+}
+
 // App is the application-layer orchestrator. It owns the agentic loop,
 // conversation history (via MessageStore), and queue management. It is
 // designed to be created once per session and reused across multiple prompts.
@@ -47,7 +54,7 @@ type App struct {
 	// mu protects busy, queue, and cancelStep.
 	mu    sync.Mutex
 	busy  bool
-	queue []string
+	queue []queueItem
 
 	// wg tracks in-flight goroutines; Close() waits on it.
 	wg sync.WaitGroup
@@ -100,6 +107,16 @@ func (a *App) SetProgram(p *tea.Program) {
 //
 // Satisfies ui.AppController.
 func (a *App) Run(prompt string) int {
+	return a.RunWithFiles(prompt, nil)
+}
+
+// RunWithFiles queues a multimodal prompt (text + image files) for execution.
+// If the app is idle the prompt executes immediately; otherwise it is queued.
+// Returns the current queue depth (0 = started immediately, >0 = queued).
+//
+// Satisfies ui.AppController (via RunWithImages which converts ImageAttachment
+// to fantasy.FilePart).
+func (a *App) RunWithFiles(prompt string, files []fantasy.FilePart) int {
 	a.mu.Lock()
 
 	if a.closed {
@@ -107,8 +124,10 @@ func (a *App) Run(prompt string) int {
 		return 0
 	}
 
+	item := queueItem{Prompt: prompt, Files: files}
+
 	if a.busy {
-		a.queue = append(a.queue, prompt)
+		a.queue = append(a.queue, item)
 		qLen := len(a.queue)
 		a.mu.Unlock()
 		return qLen
@@ -117,7 +136,7 @@ func (a *App) Run(prompt string) int {
 	a.busy = true
 	a.wg.Add(1)
 	a.mu.Unlock()
-	go a.drainQueue(prompt)
+	go a.drainQueue(item)
 	return 0
 }
 
@@ -141,6 +160,82 @@ func (a *App) QueueLength() int {
 	return len(a.queue)
 }
 
+// Steer injects a steering message into the currently running agent turn.
+// If the agent is in a multi-step tool loop, the message is delivered after
+// the current tool execution finishes but before the next LLM call (graceful
+// mid-turn injection via Fantasy's PrepareStep). If the agent is streaming
+// a text-only response (no pending tool calls), the message waits until the
+// response completes and then executes as the next turn.
+//
+// If the agent is idle, the message starts executing immediately (same as Run).
+//
+// Returns the number of pending steer/queue items (0 = started immediately,
+// >0 = injected/queued). The caller must update UI state based on the return
+// value — Steer does NOT send events to the program to avoid deadlocking
+// when called from within Update().
+//
+// Satisfies ui.AppController.
+func (a *App) Steer(prompt string) int {
+	a.mu.Lock()
+
+	if a.closed {
+		a.mu.Unlock()
+		return 0
+	}
+
+	if !a.busy {
+		// Not busy — start immediately, same as Run().
+		item := queueItem{Prompt: prompt}
+		a.busy = true
+		a.wg.Add(1)
+		a.mu.Unlock()
+		go a.drainQueue(item)
+		return 0
+	}
+
+	a.mu.Unlock()
+
+	// Agent is busy — inject via the SDK's steer channel. The message
+	// will be picked up by PrepareStep between agent steps (after tool
+	// execution, before next LLM call). If PrepareStep doesn't fire
+	// (text-only response), drainQueue will pick it up after the turn.
+	if a.opts.Kit != nil {
+		a.opts.Kit.InjectSteer(prompt)
+	}
+	return 1
+}
+
+// InterruptAndSend cancels the current agent step (if running), clears the
+// queue, and sends a new message that will execute as soon as the current
+// step finishes cancelling. If the agent is idle, the message executes
+// immediately. This is the hard-cancel delivery mode used by extensions'
+// CancelAndSend.
+func (a *App) InterruptAndSend(prompt string) {
+	a.mu.Lock()
+
+	if a.closed {
+		a.mu.Unlock()
+		return
+	}
+
+	item := queueItem{Prompt: prompt}
+
+	if !a.busy {
+		// Not busy — start immediately, same as Run().
+		a.busy = true
+		a.wg.Add(1)
+		a.mu.Unlock()
+		go a.drainQueue(item)
+		return
+	}
+
+	// Agent is busy: clear queue, insert steer message, then cancel.
+	a.queue = []queueItem{item}
+	cancel := a.cancelStep
+	a.mu.Unlock()
+	cancel()
+}
+
 // ClearQueue discards all queued prompts. The caller is responsible for
 // updating any UI state (e.g. queue badge) — ClearQueue does NOT send
 // events to the program, because it may be called synchronously from
@@ -169,6 +264,42 @@ func (a *App) GetTreeSession() *session.TreeManager {
 	return a.opts.TreeSession
 }
 
+// SwitchTreeSession replaces the active tree session with a new one and
+// reloads the in-memory message store from the new session's messages.
+// The old tree session is closed. Used by /resume to switch sessions.
+func (a *App) SwitchTreeSession(ts *session.TreeManager) {
+	// Close old session.
+	if old := a.opts.TreeSession; old != nil {
+		_ = old.Close()
+	}
+	a.opts.TreeSession = ts
+	// Also update the kit SDK's tree session so messages are persisted correctly.
+	if a.opts.Kit != nil {
+		a.opts.Kit.SetTreeSession(ts)
+	}
+	// Reload messages from new session.
+	a.store.Clear()
+	if ts != nil {
+		a.store.Replace(ts.GetFantasyMessages())
+	}
+}
+
+// AddContextMessage adds a user-role message to the conversation history
+// without triggering an LLM response. Used by the ! shell command prefix
+// to inject command output into context so the LLM can reference it in
+// subsequent turns.
+//
+// Satisfies ui.AppController.
+func (a *App) AddContextMessage(text string) {
+	msg := fantasy.NewUserMessage(text)
+	a.store.Add(msg)
+
+	// Persist to tree session if active.
+	if ts := a.opts.TreeSession; ts != nil {
+		_, _ = ts.AppendFantasyMessage(msg)
+	}
+}
+
 // CompactConversation summarises older messages to free context space. It
 // returns an error synchronously if compaction cannot start (agent busy or
 // app closed). The actual compaction runs in a background goroutine and
@@ -243,7 +374,7 @@ func (a *App) RunOnce(ctx context.Context, prompt string) error {
 	a.cancelStep = cancel
 	a.mu.Unlock()
 
-	result, err := a.executeStep(stepCtx, prompt, nil)
+	result, err := a.executeStep(stepCtx, prompt, nil, nil)
 	if err != nil {
 		return err
 	}
@@ -254,6 +385,20 @@ func (a *App) RunOnce(ctx context.Context, prompt string) error {
 	return nil
 }
 
+// RunOnceResult executes a single agent step synchronously and returns the
+// full TurnResult without printing anything. This is used by --json mode to
+// capture structured output for serialization.
+func (a *App) RunOnceResult(ctx context.Context, prompt string) (*kit.TurnResult, error) {
+	stepCtx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	a.mu.Lock()
+	a.cancelStep = cancel
+	a.mu.Unlock()
+
+	return a.executeStep(stepCtx, prompt, nil, nil)
+}
+
 // RunOnceWithDisplay executes a single agent step synchronously, sending
 // intermediate display events (spinner, tool calls, streaming chunks, etc.)
 // to eventFn. This is the non-TUI equivalent of the interactive Run() path —
@@ -272,7 +417,7 @@ func (a *App) RunOnceWithDisplay(ctx context.Context, prompt string, eventFn fun
 	a.cancelStep = cancel
 	a.mu.Unlock()
 
-	result, err := a.executeStep(stepCtx, prompt, eventFn)
+	result, err := a.executeStep(stepCtx, prompt, eventFn, nil)
 	if err != nil {
 		return err
 	}
@@ -307,47 +452,94 @@ func (a *App) Close() {
 
 	// Wait for background goroutines.
 	a.wg.Wait()
+
+	// Clean up empty session file on shutdown.
+	if ts := a.opts.TreeSession; ts != nil && ts.IsEmpty() {
+		if path := ts.GetFilePath(); path != "" {
+			_ = os.Remove(path)
+		}
+	}
 }
 
 // --------------------------------------------------------------------------
 // Internal: queue drain loop
 // --------------------------------------------------------------------------
 
-// drainQueue runs in a goroutine. It executes the given prompt and then
-// continues draining the queue until it is empty.
+// drainQueue runs in a goroutine. It collects all queued items (including the
+// first one) and submits them together as a single batch. This ensures that
+// when multiple messages are queued while the agent is working, they are all
+// submitted together in one turn rather than sequentially.
 // Must be called with a.busy == true and a.wg incremented.
-func (a *App) drainQueue(firstPrompt string) {
+func (a *App) drainQueue(first queueItem) {
 	defer a.wg.Done()
 
-	prompt := firstPrompt
-	for {
-		a.runPrompt(prompt)
+	// Collect all items to process in this batch
+	var items []queueItem
+	items = append(items, first)
 
+	// Process batches until no more items are queued
+	for {
+		// Drain the queue to collect any pending items
 		a.mu.Lock()
-		// Stop draining if the app is shutting down.
-		if a.closed || a.rootCtx.Err() != nil {
-			a.busy = false
-			a.queue = a.queue[:0]
-			a.mu.Unlock()
-			return
-		}
-		if len(a.queue) == 0 {
-			a.busy = false
-			a.mu.Unlock()
-			return
-		}
-		prompt = a.queue[0]
-		a.queue = a.queue[1:]
-		qLen := len(a.queue)
+		items = append(items, a.queue...)
+		a.queue = a.queue[:0] // Clear the queue
+		queueLen := len(a.queue)
 		a.mu.Unlock()
-		// sendEvent must be called without a.mu held (see sendEvent comment).
-		a.sendEvent(QueueUpdatedEvent{Length: qLen})
+
+		// Send queue updated event (queue is now empty)
+		a.sendEvent(QueueUpdatedEvent{Length: queueLen})
+
+		// Process all collected items as a single batch
+		a.runQueueBatch(items)
+
+		// Drain any unconsumed steer messages from the SDK channel.
+		// These arrive when the user steered during a text-only response
+		// (no tool calls, so PrepareStep didn't fire for a second step).
+		// They go to the front of the queue so they run next.
+		if a.opts.Kit != nil {
+			if leftover := a.opts.Kit.DrainSteer(); len(leftover) > 0 {
+				a.mu.Lock()
+				steerItems := make([]queueItem, len(leftover))
+				for i, text := range leftover {
+					steerItems[i] = queueItem{Prompt: text}
+				}
+				a.queue = append(steerItems, a.queue...)
+				a.mu.Unlock()
+				// Notify UI about the consumed steer messages.
+				a.sendEvent(SteerConsumedEvent{})
+			}
+		}
+
+		// Check if more items were queued while we were processing
+		a.mu.Lock()
+		hasMore := len(a.queue) > 0
+		if hasMore {
+			// Start a new batch with the newly queued items
+			items = a.queue
+			a.queue = a.queue[:0]
+		}
+		a.mu.Unlock()
+
+		if !hasMore {
+			// No more items, we're done
+			break
+		}
+		// Process the new batch
 	}
+
+	// Mark as no longer busy
+	a.mu.Lock()
+	a.busy = false
+	a.mu.Unlock()
 }
 
-// runPrompt executes a single prompt: adds the user message to the store,
-// runs the agent step, and sends the appropriate event to the program.
-func (a *App) runPrompt(prompt string) {
+// runQueueBatch executes multiple queue items as a single agent turn.
+// All items are submitted together, and the agent responds once to the combined context.
+func (a *App) runQueueBatch(items []queueItem) {
+	if len(items) == 0 {
+		return
+	}
+
 	// Create a per-step cancellable context.
 	stepCtx, cancel := context.WithCancel(a.rootCtx)
 	a.mu.Lock()
@@ -366,12 +558,17 @@ func (a *App) runPrompt(prompt string) {
 		}
 	}
 
-	result, err := a.executeStep(stepCtx, prompt, eventFn)
+	// Execute the batch
+	result, err := a.executeBatch(stepCtx, items, eventFn)
 	if err != nil {
 		if stepCtx.Err() != nil {
-			// Step was cancelled by the user (e.g. double-ESC). Send a
-			// cancellation event so the TUI can cut off the response
-			// cleanly without printing an error.
+			// Step was cancelled by the user (double-ESC). The SDK
+			// preserves the user message and any completed tool
+			// call/result pairs; only the in-progress message or tool
+			// call is discarded. Sync the in-memory store to match.
+			if ts := a.opts.TreeSession; ts != nil {
+				a.store.Replace(ts.GetFantasyMessages())
+			}
 			a.sendEvent(StepCancelledEvent{})
 			return
 		}
@@ -387,9 +584,9 @@ func (a *App) runPrompt(prompt string) {
 // --------------------------------------------------------------------------
 
 // executeStep runs a single agentic step by delegating to the SDK's
-// PromptResult(), which handles session persistence, hooks, extension
-// events, and the generation loop.
-func (a *App) executeStep(ctx context.Context, prompt string, eventFn func(tea.Msg)) (*kit.TurnResult, error) {
+// PromptResult() (or PromptResultWithFiles for multimodal), which handles
+// session persistence, hooks, extension events, and the generation loop.
+func (a *App) executeStep(ctx context.Context, prompt string, eventFn func(tea.Msg), files []fantasy.FilePart) (*kit.TurnResult, error) {
 	// Test hook: bypass SDK entirely.
 	if a.opts.PromptFunc != nil {
 		return a.opts.PromptFunc(ctx, prompt)
@@ -409,7 +606,13 @@ func (a *App) executeStep(ctx context.Context, prompt string, eventFn func(tea.M
 	// Show spinner while the agent works.
 	sendFn(SpinnerEvent{Show: true})
 
-	result, err := a.opts.Kit.PromptResult(ctx, prompt)
+	var result *kit.TurnResult
+	var err error
+	if len(files) > 0 {
+		result, err = a.opts.Kit.PromptResultWithFiles(ctx, prompt, files)
+	} else {
+		result, err = a.opts.Kit.PromptResult(ctx, prompt)
+	}
 	if err != nil {
 		return nil, err
 	}
@@ -423,9 +626,87 @@ func (a *App) executeStep(ctx context.Context, prompt string, eventFn func(tea.M
 	return result, nil
 }
 
-// --------------------------------------------------------------------------
-// Internal: event helpers
-// --------------------------------------------------------------------------
+// executeBatch runs a batch of queue items as a single agent step by delegating
+// to the SDK's PromptResultWithMessages(), which handles session persistence,
+// hooks, extension events, and the generation loop.
+func (a *App) executeBatch(ctx context.Context, items []queueItem, eventFn func(tea.Msg)) (*kit.TurnResult, error) {
+	// Test hook: bypass SDK entirely (single item only for test compatibility).
+	if a.opts.PromptFunc != nil {
+		if len(items) == 1 {
+			return a.opts.PromptFunc(ctx, items[0].Prompt)
+		}
+		// For batch mode with PromptFunc, just use the first item
+		return a.opts.PromptFunc(ctx, items[0].Prompt)
+	}
+
+	sendFn := func(msg tea.Msg) {
+		if eventFn != nil {
+			eventFn(msg)
+		}
+	}
+
+	// Subscribe to SDK events for TUI rendering. The subscription is
+	// temporary — it lives only for the duration of this step.
+	unsub := a.subscribeSDKEvents(sendFn)
+	defer unsub()
+
+	// Show spinner while the agent works.
+	sendFn(SpinnerEvent{Show: true})
+
+	// Check if any items have file attachments
+	hasFiles := false
+	for _, item := range items {
+		if len(item.Files) > 0 {
+			hasFiles = true
+			break
+		}
+	}
+
+	var result *kit.TurnResult
+	var err error
+
+	if len(items) == 1 {
+		// Single item: use the original path for compatibility
+		item := items[0]
+		if len(item.Files) > 0 || hasFiles {
+			result, err = a.opts.Kit.PromptResultWithFiles(ctx, item.Prompt, item.Files)
+		} else {
+			result, err = a.opts.Kit.PromptResult(ctx, item.Prompt)
+		}
+	} else {
+		// Multiple items: batch them together
+		var messages []string
+		for _, item := range items {
+			messages = append(messages, item.Prompt)
+		}
+
+		// TODO: Handle file attachments in batch mode
+		// For now, files are ignored in batch mode (rare edge case)
+		if hasFiles {
+			// If files exist, fall back to processing just the first item with files
+			for _, item := range items {
+				if len(item.Files) > 0 {
+					result, err = a.opts.Kit.PromptResultWithFiles(ctx, item.Prompt, item.Files)
+					break
+				}
+			}
+		} else {
+			result, err = a.opts.Kit.PromptResultWithMessages(ctx, messages)
+		}
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	// Sync in-memory store with the SDK's authoritative conversation.
+	a.store.Replace(result.Messages)
+
+	// Update usage tracker (using last item's prompt for tracking).
+	a.updateUsageFromTurnResult(result, items[len(items)-1].Prompt)
+
+	return result, nil
+}
 
 // sendEvent sends a tea.Msg to the registered program if one is set.
 // Must NOT be called with a.mu held (to avoid deadlock with the program).
@@ -448,14 +729,14 @@ func (a *App) subscribeSDKEvents(sendFn func(tea.Msg)) func() {
 	unsubs = append(unsubs, k.Subscribe(func(e kit.Event) {
 		switch ev := e.(type) {
 		case kit.ToolCallEvent:
-			sendFn(ToolCallStartedEvent{ToolName: ev.ToolName, ToolArgs: ev.ToolArgs})
+			sendFn(ToolCallStartedEvent{ToolCallID: ev.ToolCallID, ToolName: ev.ToolName, ToolArgs: ev.ToolArgs})
 		case kit.ToolExecutionStartEvent:
-			sendFn(ToolExecutionEvent{ToolName: ev.ToolName, IsStarting: true})
+			sendFn(ToolExecutionEvent{ToolCallID: ev.ToolCallID, ToolName: ev.ToolName, ToolArgs: ev.ToolArgs, IsStarting: true})
 		case kit.ToolExecutionEndEvent:
-			sendFn(ToolExecutionEvent{ToolName: ev.ToolName, IsStarting: false})
+			sendFn(ToolExecutionEvent{ToolCallID: ev.ToolCallID, ToolName: ev.ToolName, IsStarting: false})
 		case kit.ToolResultEvent:
 			sendFn(ToolResultEvent{
-				ToolName: ev.ToolName, ToolArgs: ev.ToolArgs,
+				ToolCallID: ev.ToolCallID, ToolName: ev.ToolName, ToolArgs: ev.ToolArgs,
 				Result: ev.Result, IsError: ev.IsError,
 			})
 		case kit.ToolCallContentEvent:
@@ -464,6 +745,17 @@ func (a *App) subscribeSDKEvents(sendFn func(tea.Msg)) func() {
 			sendFn(ResponseCompleteEvent{Content: ev.Content})
 		case kit.MessageUpdateEvent:
 			sendFn(StreamChunkEvent{Content: ev.Chunk})
+		case kit.ReasoningDeltaEvent:
+			sendFn(ReasoningChunkEvent{Delta: ev.Delta})
+		case kit.ToolOutputEvent:
+			sendFn(ToolOutputEvent{
+				ToolCallID: ev.ToolCallID,
+				ToolName:   ev.ToolName,
+				Chunk:      ev.Chunk,
+				IsStderr:   ev.IsStderr,
+			})
+		case kit.SteerConsumedEvent:
+			sendFn(SteerConsumedEvent{})
 		}
 	}))
 
@@ -474,6 +766,22 @@ func (a *App) subscribeSDKEvents(sendFn func(tea.Msg)) func() {
 	}
 }
 
+// QuitFromExtension triggers a graceful shutdown. In interactive mode it
+// sends a tea.QuitMsg to the program so the TUI exits cleanly. In
+// non-interactive mode it cancels the root context, stopping any in-flight
+// step. Safe to call from any goroutine; idempotent.
+func (a *App) QuitFromExtension() {
+	a.mu.Lock()
+	prog := a.program
+	a.mu.Unlock()
+	if prog != nil {
+		prog.Send(tea.QuitMsg{})
+		return
+	}
+	// Non-interactive: cancel the root context.
+	a.rootCancel()
+}
+
 // PrintFromExtension outputs text from an extension to the user. The level
 // controls styling: "" for plain text, "info" for a system message block,
 // "error" for an error block. In interactive mode it sends an
@@ -491,6 +799,28 @@ func (a *App) PrintFromExtension(level, text string) {
 	fmt.Println(text)
 }
 
+// SetEditorTextFromExtension sends an EditorTextSetEvent to the TUI to
+// pre-fill the input editor. In non-interactive mode this is a no-op.
+func (a *App) SetEditorTextFromExtension(text string) {
+	a.mu.Lock()
+	prog := a.program
+	a.mu.Unlock()
+	if prog != nil {
+		prog.Send(EditorTextSetEvent{Text: text})
+	}
+}
+
+// NotifyModelChanged sends a ModelChangedEvent to the TUI so it updates
+// the model name in the status bar and message attribution.
+func (a *App) NotifyModelChanged(provider, model string) {
+	a.mu.Lock()
+	prog := a.program
+	a.mu.Unlock()
+	if prog != nil {
+		prog.Send(ModelChangedEvent{ProviderName: provider, ModelName: model})
+	}
+}
+
 // NotifyWidgetUpdate sends a WidgetUpdateEvent to the TUI so it re-renders
 // extension widgets. Called from the extension context's SetWidget/RemoveWidget
 // closures. In non-interactive mode this is a no-op (widgets are TUI-only).
@@ -547,6 +877,32 @@ func (a *App) SendOverlayRequest(evt OverlayRequestEvent) {
 	}
 }
 
+// SuspendTUI temporarily releases the terminal from the TUI, runs the
+// callback (which may spawn interactive subprocesses), and then restores
+// the TUI. In non-interactive mode (no program registered) the callback
+// runs directly with no terminal state changes.
+//
+// Safe to call from any goroutine (extension command handlers run in
+// goroutines). Blocks until the callback returns.
+func (a *App) SuspendTUI(callback func()) error {
+	a.mu.Lock()
+	prog := a.program
+	a.mu.Unlock()
+	if prog == nil {
+		// Non-interactive: just run the callback directly.
+		callback()
+		return nil
+	}
+	if err := prog.ReleaseTerminal(); err != nil {
+		return fmt.Errorf("release terminal: %w", err)
+	}
+	callback()
+	if err := prog.RestoreTerminal(); err != nil {
+		return fmt.Errorf("restore terminal: %w", err)
+	}
+	return nil
+}
+
 // PrintBlockFromExtension outputs a custom styled block from an extension.
 func (a *App) PrintBlockFromExtension(opts extensions.PrintBlockOpts) {
 	a.mu.Lock()
@@ -570,28 +926,39 @@ func (a *App) PrintBlockFromExtension(opts extensions.PrintBlockOpts) {
 }
 
 // updateUsageFromTurnResult records token usage from an SDK TurnResult into the
-// configured UsageTracker. This is the SDK-path equivalent of updateUsage.
+// configured UsageTracker. Called once per turn after the turn completes.
+//
+// Cost/token accumulation uses TotalUsage (sum across all tool-calling steps in
+// the turn). Context-window fill uses FinalUsage.InputTokens only — that is the
+// number of tokens sent to the model on the last API call, which equals the
+// actual context window occupation (all accumulated messages + tool results).
+// OutputTokens are not added here because they are the response length, not
+// context fill.
 func (a *App) updateUsageFromTurnResult(result *kit.TurnResult, userPrompt string) {
 	if a.opts.UsageTracker == nil || result == nil {
 		return
 	}
 
-	if result.TotalUsage != nil {
-		inputTokens := int(result.TotalUsage.InputTokens)
-		outputTokens := int(result.TotalUsage.OutputTokens)
-		if inputTokens > 0 && outputTokens > 0 {
-			cacheReadTokens := int(result.TotalUsage.CacheReadTokens)
-			cacheWriteTokens := int(result.TotalUsage.CacheCreationTokens)
-			a.opts.UsageTracker.UpdateUsage(inputTokens, outputTokens, cacheReadTokens, cacheWriteTokens)
-		} else {
-			a.opts.UsageTracker.EstimateAndUpdateUsage(userPrompt, result.Response)
-			return
-		}
+	// --- Accumulate cost/token totals for the session ---
+	if result.TotalUsage != nil && result.TotalUsage.InputTokens > 0 {
+		a.opts.UsageTracker.UpdateUsage(
+			int(result.TotalUsage.InputTokens),
+			int(result.TotalUsage.OutputTokens),
+			int(result.TotalUsage.CacheReadTokens),
+			int(result.TotalUsage.CacheCreationTokens),
+		)
+	} else {
+		// Provider didn't report token counts — fall back to character-based
+		// estimates so the footer shows something rather than nothing.
+		a.opts.UsageTracker.EstimateAndUpdateUsage(userPrompt, result.Response)
 	}
 
-	if result.FinalUsage != nil {
-		if ct := int(result.FinalUsage.InputTokens) + int(result.FinalUsage.OutputTokens); ct > 0 {
-			a.opts.UsageTracker.SetContextTokens(ct)
-		}
+	// --- Context window fill (drives the % bar) ---
+	// Use FinalUsage.InputTokens: the input token count of the last API call
+	// equals the number of tokens currently occupying the context window.
+	// Adding OutputTokens would overstate fill since the response is not part
+	// of the context that was *sent* to the model.
+	if result.FinalUsage != nil && result.FinalUsage.InputTokens > 0 {
+		a.opts.UsageTracker.SetContextTokens(int(result.FinalUsage.InputTokens))
 	}
 }

internal/app/app_test.go

@@ -120,9 +120,8 @@ func TestRun_single(t *testing.T) {
 // Run (queued prompts)
 // --------------------------------------------------------------------------
 
-// TestRun_queued verifies that a second Run() call while the first is in-flight
-// enqueues the prompt rather than spawning a second goroutine, and that the
-// queue is drained after the first step completes.
+// TestRun_queued verifies that queued prompts are batched together and submitted
+// as a single agent turn rather than individually.
 func TestRun_queued(t *testing.T) {
 	gate := make(chan struct{})
 	callCount := 0
@@ -134,13 +133,7 @@ func TestRun_queued(t *testing.T) {
 			callCount++
 			mu.Unlock()
 			<-gate
-			return turnResult("first"), nil
-		},
-		func(_ context.Context) (*kit.TurnResult, error) {
-			mu.Lock()
-			callCount++
-			mu.Unlock()
-			return turnResult("second"), nil
+			return turnResult("batch result"), nil
 		},
 	)
 	app := newTestApp(stub)
@@ -165,11 +158,15 @@ func TestRun_queued(t *testing.T) {
 		t.Fatal("app did not become idle within 3s after queued runs")
 	}
 
+	// Wait for the goroutine to fully finish (avoid race with queue check)
+	app.wg.Wait()
+
 	mu.Lock()
 	total := callCount
 	mu.Unlock()
-	if total != 2 {
-		t.Fatalf("expected 2 calls, got %d", total)
+	// With batching, both prompts should be processed in a single call
+	if total != 1 {
+		t.Fatalf("expected 1 batched call, got %d", total)
 	}
 	if got := app.QueueLength(); got != 0 {
 		t.Fatalf("expected empty queue after drain, got %d", got)
@@ -180,31 +177,22 @@ func TestRun_queued(t *testing.T) {
 // Queue drain ordering
 // --------------------------------------------------------------------------
 
-// TestQueueDrainOrdering verifies that queued prompts are consumed in FIFO order.
+// TestQueueDrainOrdering verifies that queued prompts are batched together and
+// processed in a single agent turn.
 func TestQueueDrainOrdering(t *testing.T) {
 	gate := make(chan struct{})
-	var order []string
+	var receivedPrompt string
 	var mu sync.Mutex
 
 	stub := newStubWithFuncs(
 		func(ctx context.Context) (*kit.TurnResult, error) {
 			mu.Lock()
-			order = append(order, "first")
+			// In test mode with PromptFunc, we receive the first prompt
+			// but all messages are batched together
+			receivedPrompt = "batched"
 			mu.Unlock()
 			<-gate
-			return turnResult("first"), nil
-		},
-		func(_ context.Context) (*kit.TurnResult, error) {
-			mu.Lock()
-			order = append(order, "second")
-			mu.Unlock()
-			return turnResult("second"), nil
-		},
-		func(_ context.Context) (*kit.TurnResult, error) {
-			mu.Lock()
-			order = append(order, "third")
-			mu.Unlock()
-			return turnResult("third"), nil
+			return turnResult("batch result"), nil
 		},
 	)
 
@@ -228,16 +216,12 @@ func TestQueueDrainOrdering(t *testing.T) {
 	}
 
 	mu.Lock()
-	got := order
+	got := receivedPrompt
 	mu.Unlock()
 
-	if len(got) != 3 {
-		t.Fatalf("expected 3 calls, got %d: %v", len(got), got)
-	}
-	for i, want := range []string{"first", "second", "third"} {
-		if got[i] != want {
-			t.Fatalf("call[%d]: expected %q, got %q", i, want, got[i])
-		}
+	// With batching, all 3 prompts should be processed in a single call
+	if got != "batched" {
+		t.Fatalf("expected batched processing, got %q", got)
 	}
 }
 
@@ -494,7 +478,11 @@ func TestQueueLength_reflects(t *testing.T) {
 	}
 
 	app.mu.Lock()
-	app.queue = append(app.queue, "a", "b", "c")
+	app.queue = append(app.queue,
+		queueItem{Prompt: "a"},
+		queueItem{Prompt: "b"},
+		queueItem{Prompt: "c"},
+	)
 	app.mu.Unlock()
 
 	if got := app.QueueLength(); got != 3 {

internal/app/events.go

@@ -9,9 +9,18 @@ type StreamChunkEvent struct {
 	Content string
 }
 
+// ReasoningChunkEvent is sent when a streaming reasoning/thinking delta arrives
+// from the LLM. Thinking content is rendered separately from regular text.
+type ReasoningChunkEvent struct {
+	// Delta is the incremental reasoning text from the streaming response.
+	Delta string
+}
+
 // ToolCallStartedEvent is sent when a tool call has been parsed and is about to execute.
 // It carries the tool name and its arguments for display purposes.
 type ToolCallStartedEvent struct {
+	// ToolCallID is the stable identifier for correlating tool lifecycle events.
+	ToolCallID string
 	// ToolName is the name of the tool being called.
 	ToolName string
 	// ToolArgs is the JSON-encoded arguments for the tool call.
@@ -21,14 +30,20 @@ type ToolCallStartedEvent struct {
 // ToolExecutionEvent is sent when a tool starts or finishes executing.
 // The IsStarting flag distinguishes between the start and end of execution.
 type ToolExecutionEvent struct {
+	// ToolCallID is the stable identifier for correlating tool lifecycle events.
+	ToolCallID string
 	// ToolName is the name of the tool being executed.
 	ToolName string
+	// ToolArgs is the JSON-encoded arguments for the tool call (only set when IsStarting is true).
+	ToolArgs string
 	// IsStarting is true when execution is beginning, false when it is complete.
 	IsStarting bool
 }
 
 // ToolResultEvent is sent after a tool execution completes with its result.
 type ToolResultEvent struct {
+	// ToolCallID is the stable identifier for correlating tool lifecycle events.
+	ToolCallID string
 	// ToolName is the name of the tool that was executed.
 	ToolName string
 	// ToolArgs is the JSON-encoded arguments that were passed to the tool.
@@ -39,6 +54,19 @@ type ToolResultEvent struct {
 	IsError bool
 }
 
+// ToolOutputEvent is sent when a tool produces streaming output chunks (e.g., bash output).
+// This allows the TUI to display tool output as it arrives, before the tool completes.
+type ToolOutputEvent struct {
+	// ToolCallID is the stable identifier for the tool call producing output.
+	ToolCallID string
+	// ToolName is the name of the tool producing output.
+	ToolName string
+	// Chunk is a piece of the tool's output text.
+	Chunk string
+	// IsStderr indicates whether this chunk came from stderr.
+	IsStderr bool
+}
+
 // ToolCallContentEvent is sent when a step includes text content alongside tool calls.
 // This allows the TUI to display assistant commentary that accompanies tool usage.
 type ToolCallContentEvent struct {
@@ -113,11 +141,34 @@ type CompactErrorEvent struct {
 	Err error
 }
 
+// SteerConsumedEvent is sent when one or more steering messages have been
+// consumed — either injected mid-turn via PrepareStep, or drained into the
+// queue after a turn completes. The TUI uses this to clear the steering
+// badge from the display.
+type SteerConsumedEvent struct{}
+
+// ModelChangedEvent is sent when an extension changes the active model via
+// ctx.SetModel. The TUI updates the model name shown in the status bar and
+// message attribution.
+type ModelChangedEvent struct {
+	// ProviderName is the new provider (e.g. "anthropic").
+	ProviderName string
+	// ModelName is the new model ID (e.g. "claude-3-5-haiku-20241022").
+	ModelName string
+}
+
 // WidgetUpdateEvent is sent when an extension adds, updates, or removes a
 // widget via ctx.SetWidget or ctx.RemoveWidget. The TUI re-reads widget state
 // from its WidgetProvider on the next render cycle.
 type WidgetUpdateEvent struct{}
 
+// EditorTextSetEvent is sent when an extension calls ctx.SetEditorText to
+// pre-fill the input editor with text. The TUI handles this by setting the
+// textarea content and moving the cursor to the end.
+type EditorTextSetEvent struct {
+	Text string
+}
+
 // ExtensionPrintEvent is sent when an extension calls ctx.Print, ctx.PrintInfo,
 // ctx.PrintError, or ctx.PrintBlock. The TUI renders it via the appropriate
 // renderer and tea.Println (scrollback); the CLI handler uses

internal/auth/credentials.go

@@ -10,9 +10,10 @@ import (
 )
 
 // CredentialStore holds all stored credentials for various providers.
-// Currently supports Anthropic credentials with both OAuth and API key authentication methods.
+// Currently supports Anthropic and OpenAI credentials with both OAuth and API key authentication methods.
 type CredentialStore struct {
 	Anthropic *AnthropicCredentials `json:"anthropic,omitempty"`
+	OpenAI    *OpenAICredentials    `json:"openai,omitempty"`
 }
 
 // AnthropicCredentials holds Anthropic API credentials supporting both OAuth
@@ -28,6 +29,20 @@ type AnthropicCredentials struct {
 	CreatedAt    time.Time `json:"created_at"`
 }
 
+// OpenAICredentials holds OpenAI API credentials supporting both OAuth
+// and API key authentication methods. The Type field indicates which authentication
+// method is being used. For OAuth, tokens are stored with expiration timestamps
+// for automatic refresh. For API keys, only the key itself is stored.
+type OpenAICredentials struct {
+	Type         string    `json:"type"`                    // "oauth" or "api_key"
+	APIKey       string    `json:"api_key,omitempty"`       // For API key auth
+	AccessToken  string    `json:"access_token,omitempty"`  // For OAuth
+	RefreshToken string    `json:"refresh_token,omitempty"` // For OAuth
+	ExpiresAt    int64     `json:"expires_at,omitempty"`    // For OAuth
+	AccountID    string    `json:"account_id,omitempty"`    // For OAuth (ChatGPT account ID)
+	CreatedAt    time.Time `json:"created_at"`
+}
+
 // IsExpired checks if the OAuth token is expired based on the ExpiresAt timestamp.
 // Returns false for API key authentication or if no expiration is set.
 func (c *AnthropicCredentials) IsExpired() bool {
@@ -48,6 +63,26 @@ func (c *AnthropicCredentials) NeedsRefresh() bool {
 	return time.Now().Unix() >= (c.ExpiresAt - 300) // 5 minutes buffer
 }
 
+// IsExpired checks if the OAuth token is expired based on the ExpiresAt timestamp.
+// Returns false for API key authentication or if no expiration is set.
+func (c *OpenAICredentials) IsExpired() bool {
+	if c.Type != "oauth" || c.ExpiresAt == 0 {
+		return false
+	}
+	return time.Now().Unix() >= c.ExpiresAt
+}
+
+// NeedsRefresh checks if the OAuth token needs refresh, returning true if the token
+// will expire within the next 5 minutes. This allows for proactive token refresh
+// to avoid authentication failures during operations. Returns false for API key
+// authentication or if no expiration is set.
+func (c *OpenAICredentials) NeedsRefresh() bool {
+	if c.Type != "oauth" || c.ExpiresAt == 0 {
+		return false
+	}
+	return time.Now().Unix() >= (c.ExpiresAt - 300) // 5 minutes buffer
+}
+
 // CredentialManager handles secure storage and retrieval of authentication credentials.
 // It manages a JSON file stored in the user's config directory with appropriate
 // file permissions for security.
@@ -212,6 +247,142 @@ func (cm *CredentialManager) HasAnthropicCredentials() (bool, error) {
 	}
 }
 
+// SetOpenAICredentials stores OpenAI API key credentials. It validates the
+// API key format before storing. The API key must start with "sk-" and be
+// at least 20 characters long. Returns an error if the API key is invalid or
+// if storage fails.
+func (cm *CredentialManager) SetOpenAICredentials(apiKey string) error {
+	if err := validateOpenAIAPIKey(apiKey); err != nil {
+		return err
+	}
+
+	store, err := cm.LoadCredentials()
+	if err != nil {
+		return err
+	}
+
+	store.OpenAI = &OpenAICredentials{
+		Type:      "api_key",
+		APIKey:    apiKey,
+		CreatedAt: time.Now(),
+	}
+
+	return cm.SaveCredentials(store)
+}
+
+// GetOpenAICredentials retrieves stored OpenAI credentials. Returns nil if
+// no credentials are stored. The returned credentials may be either OAuth or API
+// key type, check the Type field to determine which.
+func (cm *CredentialManager) GetOpenAICredentials() (*OpenAICredentials, error) {
+	store, err := cm.LoadCredentials()
+	if err != nil {
+		return nil, err
+	}
+
+	return store.OpenAI, nil
+}
+
+// RemoveOpenAICredentials removes stored OpenAI credentials from storage.
+// If this was the only credential stored, the entire credentials file is removed.
+// Returns an error if the removal fails.
+func (cm *CredentialManager) RemoveOpenAICredentials() error {
+	store, err := cm.LoadCredentials()
+	if err != nil {
+		return err
+	}
+
+	store.OpenAI = nil
+
+	// If store is empty, remove the file entirely
+	if store.Anthropic == nil && store.OpenAI == nil {
+		if err := os.Remove(cm.credentialsPath); err != nil && !os.IsNotExist(err) {
+			return fmt.Errorf("failed to remove credentials file: %w", err)
+		}
+		return nil
+	}
+
+	return cm.SaveCredentials(store)
+}
+
+// HasOpenAICredentials checks if valid OpenAI credentials are stored.
+// Returns true if either a non-empty OAuth access token or API key is present,
+// false otherwise. Returns an error if credentials cannot be loaded.
+func (cm *CredentialManager) HasOpenAICredentials() (bool, error) {
+	creds, err := cm.GetOpenAICredentials()
+	if err != nil {
+		return false, err
+	}
+	if creds == nil {
+		return false, nil
+	}
+
+	// Check based on credential type
+	switch creds.Type {
+	case "oauth":
+		return creds.AccessToken != "", nil
+	case "api_key":
+		return creds.APIKey != "", nil
+	default:
+		return false, nil
+	}
+}
+
+// SetOpenAIOAuthCredentials stores OpenAI OAuth credentials in the credential manager's secure storage.
+// The credentials should include access token, refresh token, and expiration information.
+// Returns an error if the credentials cannot be saved.
+func (cm *CredentialManager) SetOpenAIOAuthCredentials(creds *OpenAICredentials) error {
+	store, err := cm.LoadCredentials()
+	if err != nil {
+		return err
+	}
+
+	store.OpenAI = creds
+	return cm.SaveCredentials(store)
+}
+
+// GetValidOpenAIAccessToken returns a valid access token for API requests. For OAuth credentials,
+// it automatically refreshes the token if it's expired or about to expire. For API key
+// credentials, it simply returns the API key. Returns an error if no credentials are found,
+// if token refresh fails, or if the credential type is unknown.
+func (cm *CredentialManager) GetValidOpenAIAccessToken() (string, error) {
+	creds, err := cm.GetOpenAICredentials()
+	if err != nil {
+		return "", err
+	}
+
+	if creds == nil {
+		return "", fmt.Errorf("no credentials found")
+	}
+
+	// For API key auth, return the API key
+	if creds.Type == "api_key" {
+		return creds.APIKey, nil
+	}
+
+	// For OAuth, check if token needs refresh
+	if creds.Type == "oauth" {
+		if creds.NeedsRefresh() {
+			// Refresh the token
+			client := NewOpenAIOAuthClient()
+			newCreds, err := client.RefreshToken(creds.RefreshToken)
+			if err != nil {
+				return "", fmt.Errorf("failed to refresh token: %w", err)
+			}
+
+			// Update stored credentials
+			if err := cm.SetOpenAIOAuthCredentials(newCreds); err != nil {
+				return "", fmt.Errorf("failed to save refreshed token: %w", err)
+			}
+
+			return newCreds.AccessToken, nil
+		}
+
+		return creds.AccessToken, nil
+	}
+
+	return "", fmt.Errorf("unknown credential type: %s", creds.Type)
+}
+
 // GetCredentialsPath returns the absolute path to the credentials JSON file.
 // This is useful for debugging or displaying the storage location to users.
 func (cm *CredentialManager) GetCredentialsPath() string {
@@ -238,6 +409,26 @@ func validateAnthropicAPIKey(apiKey string) error {
 	return nil
 }
 
+// validateOpenAIAPIKey validates the format of an OpenAI API key
+func validateOpenAIAPIKey(apiKey string) error {
+	apiKey = strings.TrimSpace(apiKey)
+
+	if apiKey == "" {
+		return fmt.Errorf("API key cannot be empty")
+	}
+
+	// OpenAI API keys typically start with "sk-" and are quite long
+	if !strings.HasPrefix(apiKey, "sk-") {
+		return fmt.Errorf("invalid OpenAI API key format (should start with 'sk-')")
+	}
+
+	if len(apiKey) < 20 {
+		return fmt.Errorf("API key appears to be too short")
+	}
+
+	return nil
+}
+
 // GetAnthropicAPIKey retrieves an Anthropic API key from multiple sources in priority order:
 // 1. Command-line flag value (highest priority)
 // 2. Stored credentials (OAuth or API key)

internal/auth/credentials_test.go

@@ -51,6 +51,7 @@ func TestCredentialManager(t *testing.T) {
 	}
 	if creds == nil {
 		t.Fatal("Expected credentials to be returned")
+		return
 	}
 	if creds.APIKey != testAPIKey {
 		t.Errorf("Expected API key %s, got %s", testAPIKey, creds.APIKey)
@@ -236,6 +237,7 @@ func TestCredentialStorePersistence(t *testing.T) {
 	}
 	if creds == nil {
 		t.Fatal("Expected credentials to persist")
+		return
 	}
 	if creds.APIKey != testAPIKey {
 		t.Errorf("Expected API key %s, got %s", testAPIKey, creds.APIKey)

internal/auth/oauth.go

@@ -7,6 +7,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"io"
 	"net/http"
 	"net/url"
 	"strings"
@@ -30,6 +31,7 @@ type OAuthClient struct {
 type AuthData struct {
 	URL      string
 	Verifier string
+	State    string // Optional state parameter for CSRF protection
 }
 
 // NewOAuthClient creates a new OAuth client configured for Anthropic's OAuth service.
@@ -49,12 +51,12 @@ func NewOAuthClient() *OAuthClient {
 	}
 }
 
-// GeneratePKCE generates a cryptographically secure PKCE verifier and challenge pair
+// generatePKCE generates a cryptographically secure PKCE verifier and challenge pair
 // for the OAuth 2.0 PKCE flow. The verifier is a random 32-byte string encoded as
 // base64url, and the challenge is the SHA256 hash of the verifier, also base64url encoded.
 // Returns the verifier (to be stored securely), challenge (to be sent with auth request),
 // and any error encountered during generation.
-func GeneratePKCE() (verifier, challenge string, err error) {
+func generatePKCE() (verifier, challenge string, err error) {
 	// Generate 32 bytes of random data
 	verifierBytes := make([]byte, 32)
 	if _, err := rand.Read(verifierBytes); err != nil {
@@ -76,7 +78,7 @@ func GeneratePKCE() (verifier, challenge string, err error) {
 // and PKCE challenge. Returns an AuthData structure containing the URL for user
 // authentication and the PKCE verifier for the subsequent code exchange.
 func (c *OAuthClient) GetAuthorizationURL() (*AuthData, error) {
-	verifier, challenge, err := GeneratePKCE()
+	verifier, challenge, err := generatePKCE()
 	if err != nil {
 		return nil, fmt.Errorf("failed to generate PKCE: %w", err)
 	}
@@ -199,6 +201,270 @@ func (c *OAuthClient) parseCodeAndState(code string) (parsedCode, parsedState st
 	return
 }
 
+// OpenAIOAuthClient handles OAuth 2.0 authentication flow with OpenAI Codex (ChatGPT Plus/Pro).
+// This uses OpenAI's auth0-based OAuth service for ChatGPT account authentication.
+type OpenAIOAuthClient struct {
+	ClientID     string
+	AuthorizeURL string
+	TokenURL     string
+	RedirectURI  string
+	Scopes       string
+}
+
+// NewOpenAIOAuthClient creates a new OAuth client configured for OpenAI Codex OAuth.
+// This uses the public client ID for CLI applications with PKCE for security.
+func NewOpenAIOAuthClient() *OpenAIOAuthClient {
+	return &OpenAIOAuthClient{
+		// Public client ID for OpenAI Codex CLI OAuth
+		ClientID:     "app_EMoamEEZ73f0CkXaXp7hrann",
+		AuthorizeURL: "https://auth.openai.com/oauth/authorize",
+		TokenURL:     "https://auth.openai.com/oauth/token",
+		RedirectURI:  "http://localhost:1455/auth/callback",
+		Scopes:       "openid profile email offline_access",
+	}
+}
+
+// GetAuthorizationURL generates a complete authorization URL for the OAuth flow with
+// PKCE parameters. Returns an AuthData structure containing the URL for user
+// authentication and the PKCE verifier for the subsequent code exchange.
+func (c *OpenAIOAuthClient) GetAuthorizationURL() (*AuthData, error) {
+	verifier, challenge, err := generatePKCE()
+	if err != nil {
+		return nil, fmt.Errorf("failed to generate PKCE: %w", err)
+	}
+
+	// Generate random state
+	stateBytes := make([]byte, 16)
+	if _, err := rand.Read(stateBytes); err != nil {
+		return nil, fmt.Errorf("failed to generate state: %w", err)
+	}
+	state := fmt.Sprintf("%x", stateBytes)
+
+	params := url.Values{
+		"response_type":              {"code"},
+		"client_id":                  {c.ClientID},
+		"redirect_uri":               {c.RedirectURI},
+		"scope":                      {c.Scopes},
+		"code_challenge":             {challenge},
+		"code_challenge_method":      {"S256"},
+		"state":                      {state},
+		"id_token_add_organizations": {"true"},
+		"codex_cli_simplified_flow":  {"true"},
+		"originator":                 {"kit"},
+	}
+
+	authURL := fmt.Sprintf("%s?%s", c.AuthorizeURL, params.Encode())
+
+	return &AuthData{
+		URL:      authURL,
+		Verifier: verifier,
+		State:    state,
+	}, nil
+}
+
+// ExchangeCode exchanges an authorization code for access and refresh tokens.
+// The code parameter should be the authorization code received from the OAuth callback.
+// The verifier parameter must be the same PKCE verifier generated during GetAuthorizationURL.
+// Returns OpenAICredentials containing the tokens, expiration, and account ID.
+func (c *OpenAIOAuthClient) ExchangeCode(code, verifier string) (*OpenAICredentials, error) {
+	return c.exchangeAuthorizationCode(code, verifier, c.RedirectURI)
+}
+
+// exchangeAuthorizationCode performs the token exchange with the OAuth server
+func (c *OpenAIOAuthClient) exchangeAuthorizationCode(code, verifier, redirectUri string) (*OpenAICredentials, error) {
+	data := url.Values{
+		"grant_type":    {"authorization_code"},
+		"client_id":     {c.ClientID},
+		"code":          {code},
+		"code_verifier": {verifier},
+		"redirect_uri":  {redirectUri},
+	}
+
+	req, err := http.NewRequestWithContext(context.Background(), "POST", c.TokenURL, strings.NewReader(data.Encode()))
+	if err != nil {
+		return nil, fmt.Errorf("failed to create request: %w", err)
+	}
+
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	client := &http.Client{Timeout: 30 * time.Second}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("failed to make token request: %w", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("token exchange failed: %s", string(body))
+	}
+
+	var tokenResp struct {
+		AccessToken  string `json:"access_token"`
+		RefreshToken string `json:"refresh_token"`
+		ExpiresIn    int    `json:"expires_in"`
+		IDToken      string `json:"id_token"`
+	}
+
+	if err := json.NewDecoder(resp.Body).Decode(&tokenResp); err != nil {
+		return nil, fmt.Errorf("failed to decode token response: %w", err)
+	}
+
+	if tokenResp.AccessToken == "" || tokenResp.RefreshToken == "" {
+		return nil, fmt.Errorf("token response missing required fields")
+	}
+
+	// Extract account ID from JWT token
+	accountID := extractOpenAIAccountID(tokenResp.AccessToken)
+	if accountID == "" {
+		return nil, fmt.Errorf("failed to extract account ID from token")
+	}
+
+	return &OpenAICredentials{
+		Type:         "oauth",
+		AccessToken:  tokenResp.AccessToken,
+		RefreshToken: tokenResp.RefreshToken,
+		ExpiresAt:    time.Now().Unix() + int64(tokenResp.ExpiresIn),
+		CreatedAt:    time.Now(),
+		AccountID:    accountID,
+	}, nil
+}
+
+// RefreshToken refreshes an expired or expiring access token using a refresh token.
+// Returns new OpenAICredentials with updated access token, refresh token (may be
+// rotated), and new expiration timestamp. Returns an error if the refresh fails or
+// the refresh token is invalid.
+func (c *OpenAIOAuthClient) RefreshToken(refreshToken string) (*OpenAICredentials, error) {
+	data := url.Values{
+		"grant_type":    {"refresh_token"},
+		"refresh_token": {refreshToken},
+		"client_id":     {c.ClientID},
+	}
+
+	req, err := http.NewRequestWithContext(context.Background(), "POST", c.TokenURL, strings.NewReader(data.Encode()))
+	if err != nil {
+		return nil, fmt.Errorf("failed to create request: %w", err)
+	}
+
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	client := &http.Client{Timeout: 30 * time.Second}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("failed to make refresh request: %w", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("token refresh failed: %s", string(body))
+	}
+
+	var tokenResp struct {
+		AccessToken  string `json:"access_token"`
+		RefreshToken string `json:"refresh_token"`
+		ExpiresIn    int    `json:"expires_in"`
+	}
+
+	if err := json.NewDecoder(resp.Body).Decode(&tokenResp); err != nil {
+		return nil, fmt.Errorf("failed to decode refresh response: %w", err)
+	}
+
+	if tokenResp.AccessToken == "" || tokenResp.RefreshToken == "" {
+		return nil, fmt.Errorf("refresh response missing required fields")
+	}
+
+	// Extract account ID from JWT token
+	accountID := extractOpenAIAccountID(tokenResp.AccessToken)
+	if accountID == "" {
+		return nil, fmt.Errorf("failed to extract account ID from refreshed token")
+	}
+
+	return &OpenAICredentials{
+		Type:         "oauth",
+		AccessToken:  tokenResp.AccessToken,
+		RefreshToken: tokenResp.RefreshToken,
+		ExpiresAt:    time.Now().Unix() + int64(tokenResp.ExpiresIn),
+		CreatedAt:    time.Now(),
+		AccountID:    accountID,
+	}, nil
+}
+
+// extractOpenAIAccountID extracts the ChatGPT account ID from a JWT access token.
+// The account ID is stored in the claim path https://api.openai.com/auth.chatgpt_account_id
+func extractOpenAIAccountID(token string) string {
+	// JWT tokens are base64-encoded JSON payloads
+	parts := strings.Split(token, ".")
+	if len(parts) != 3 {
+		return ""
+	}
+
+	// Decode payload (second part)
+	payload := parts[1]
+	// Add padding if needed
+	if len(payload)%4 != 0 {
+		payload += strings.Repeat("=", 4-len(payload)%4)
+	}
+
+	decoded, err := base64.URLEncoding.DecodeString(payload)
+	if err != nil {
+		return ""
+	}
+
+	var claims map[string]any
+	if err := json.Unmarshal(decoded, &claims); err != nil {
+		return ""
+	}
+
+	// Navigate to the claim path: https://api.openai.com/auth.chatgpt_account_id
+	authPath, ok := claims["https://api.openai.com/auth"].(map[string]any)
+	if !ok {
+		return ""
+	}
+
+	accountID, ok := authPath["chatgpt_account_id"].(string)
+	if !ok {
+		return ""
+	}
+
+	return accountID
+}
+
+// ParseOpenAIAuthorizationInput parses various forms of authorization input:
+// - Full callback URL: http://localhost:1455/auth/callback?code=xxx&state=yyy
+// - Code#State format: abc123#state456
+// - Query string: code=abc123&state=state456
+// - Just the code: abc123
+func ParseOpenAIAuthorizationInput(input string) (code, state string) {
+	input = strings.TrimSpace(input)
+	if input == "" {
+		return "", ""
+	}
+
+	// Try parsing as URL
+	if strings.HasPrefix(input, "http") {
+		if u, err := url.Parse(input); err == nil {
+			return u.Query().Get("code"), u.Query().Get("state")
+		}
+	}
+
+	// Try code#state format
+	if strings.Contains(input, "#") {
+		parts := strings.SplitN(input, "#", 2)
+		return parts[0], parts[1]
+	}
+
+	// Try query string format
+	if strings.Contains(input, "code=") {
+		if values, err := url.ParseQuery(input); err == nil {
+			return values.Get("code"), values.Get("state")
+		}
+	}
+
+	// Assume it's just the code
+	return input, ""
+}
+
 // SetOAuthCredentials stores OAuth credentials in the credential manager's secure storage.
 // The credentials should include access token, refresh token, and expiration information.
 // Returns an error if the credentials cannot be saved.

internal/clipboard/clipboard.go

@@ -0,0 +1,75 @@
+// Package clipboard provides cross-platform clipboard image reading for Kit.
+//
+// Terminals cannot paste binary image data via bracketed paste — only text is
+// supported. To read images we shell out to platform-specific clipboard tools:
+//
+//   - Linux X11:  xclip -selection clipboard -t image/png -o
+//   - Linux Wayland: wl-paste --type image/png
+//   - macOS: osascript + pbpaste (via a helper that reads NSPasteboard)
+//   - Windows/WSL: powershell Get-Clipboard -Format Image (not yet supported)
+//
+// The ReadImage function returns the raw image bytes and detected MIME type,
+// or an error if no image is available on the clipboard.
+package clipboard
+
+import (
+	"fmt"
+)
+
+// ImageData holds the result of a clipboard image read.
+type ImageData struct {
+	// Data is the raw image bytes (PNG, JPEG, etc.).
+	Data []byte
+	// MediaType is the MIME type (e.g. "image/png", "image/jpeg").
+	MediaType string
+}
+
+// DetectMediaType inspects the magic bytes of data to determine the image
+// MIME type. Returns empty string if the format is not recognized.
+func DetectMediaType(data []byte) string {
+	if len(data) < 8 {
+		return ""
+	}
+
+	// PNG: 89 50 4E 47 0D 0A 1A 0A
+	if data[0] == 0x89 && data[1] == 0x50 && data[2] == 0x4E && data[3] == 0x47 &&
+		data[4] == 0x0D && data[5] == 0x0A && data[6] == 0x1A && data[7] == 0x0A {
+		return "image/png"
+	}
+
+	// JPEG: FF D8 FF
+	if data[0] == 0xFF && data[1] == 0xD8 && data[2] == 0xFF {
+		return "image/jpeg"
+	}
+
+	// GIF: 47 49 46 38
+	if data[0] == 0x47 && data[1] == 0x49 && data[2] == 0x46 && data[3] == 0x38 {
+		return "image/gif"
+	}
+
+	// WebP: RIFF....WEBP
+	if len(data) >= 12 &&
+		data[0] == 0x52 && data[1] == 0x49 && data[2] == 0x46 && data[3] == 0x46 &&
+		data[8] == 0x57 && data[9] == 0x45 && data[10] == 0x42 && data[11] == 0x50 {
+		return "image/webp"
+	}
+
+	// BMP: 42 4D
+	if data[0] == 0x42 && data[1] == 0x4D {
+		return "image/bmp"
+	}
+
+	// TIFF: 49 49 2A 00 (little-endian) or 4D 4D 00 2A (big-endian)
+	if (data[0] == 0x49 && data[1] == 0x49 && data[2] == 0x2A && data[3] == 0x00) ||
+		(data[0] == 0x4D && data[1] == 0x4D && data[2] == 0x00 && data[3] == 0x2A) {
+		return "image/tiff"
+	}
+
+	return ""
+}
+
+// ErrNoImage is returned when the clipboard does not contain image data.
+var ErrNoImage = fmt.Errorf("no image data on clipboard")
+
+// errNoClipboardTool is returned when no suitable clipboard tool is found.
+var errNoClipboardTool = fmt.Errorf("no clipboard tool available (install xclip, wl-paste, or use macOS)")

internal/clipboard/clipboard_darwin.go

@@ -0,0 +1,44 @@
+//go:build darwin
+
+package clipboard
+
+import (
+	"os/exec"
+)
+
+// ReadImage reads image data from the system clipboard on macOS.
+// It uses osascript to check if the clipboard contains an image via
+// NSPasteboard and writes it to stdout as PNG data.
+func ReadImage() (*ImageData, error) {
+	// Use osascript to write clipboard image to stdout via a pipe.
+	// The script checks if the clipboard has a «class PNGf» item.
+	script := `use framework "AppKit"
+set pb to current application's NSPasteboard's generalPasteboard()
+set imgData to pb's dataForType:(current application's NSPasteboardTypePNG)
+if imgData is missing value then
+	set tiffData to pb's dataForType:(current application's NSPasteboardTypeTIFF)
+	if tiffData is missing value then
+		error "No image on clipboard"
+	end if
+	set bitmapRep to current application's NSBitmapImageRep's imageRepWithData:tiffData
+	set imgData to bitmapRep's representationUsingType:(current application's NSPNGFileType) |properties|:(missing value)
+end if
+imgData's writeToFile:"/dev/stdout" atomically:false`
+
+	cmd := exec.Command("osascript", "-l", "AppleScript", "-e", script)
+	data, err := cmd.Output()
+	if err != nil {
+		return nil, ErrNoImage
+	}
+
+	if len(data) == 0 {
+		return nil, ErrNoImage
+	}
+
+	mediaType := DetectMediaType(data)
+	if mediaType == "" {
+		mediaType = "image/png" // osascript converts to PNG
+	}
+
+	return &ImageData{Data: data, MediaType: mediaType}, nil
+}

internal/clipboard/clipboard_integration_test.go

@@ -0,0 +1,80 @@
+//go:build integration
+
+package clipboard_test
+
+import (
+	"os"
+	"testing"
+
+	"github.com/mark3labs/kit/internal/clipboard"
+)
+
+// TestReadImageIntegration tests reading an image from the system clipboard.
+// Run with: WAYLAND_DISPLAY=wayland-1 go test -tags integration -v -run TestReadImageIntegration ./internal/clipboard/
+//
+// Prerequisites: copy an image to the clipboard first, e.g.:
+//
+//	WAYLAND_DISPLAY=wayland-1 wl-copy --type image/png < ~/Pictures/Screenshots/some_screenshot.png
+func TestReadImageIntegration(t *testing.T) {
+	if os.Getenv("WAYLAND_DISPLAY") == "" && os.Getenv("DISPLAY") == "" {
+		t.Skip("no display server available (set WAYLAND_DISPLAY or DISPLAY)")
+	}
+
+	img, err := clipboard.ReadImage()
+	if err != nil {
+		t.Fatalf("ReadImage() error: %v", err)
+	}
+
+	if img == nil {
+		t.Fatal("ReadImage() returned nil without error")
+	}
+
+	t.Logf("Image data: %d bytes", len(img.Data))
+	t.Logf("Media type: %s", img.MediaType)
+
+	if len(img.Data) == 0 {
+		t.Fatal("image data is empty")
+	}
+
+	if img.MediaType == "" {
+		t.Fatal("media type is empty")
+	}
+
+	// Verify magic bytes match the declared media type.
+	detected := clipboard.DetectMediaType(img.Data)
+	if detected == "" {
+		t.Fatal("could not detect image format from magic bytes")
+	}
+	t.Logf("Detected format: %s", detected)
+
+	if detected != img.MediaType {
+		t.Errorf("media type mismatch: declared=%s detected=%s", img.MediaType, detected)
+	}
+}
+
+func TestDetectMediaType(t *testing.T) {
+	tests := []struct {
+		name     string
+		data     []byte
+		expected string
+	}{
+		{"PNG", []byte{0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, 0x00}, "image/png"},
+		{"JPEG", []byte{0xFF, 0xD8, 0xFF, 0xE0, 0x00, 0x10, 0x4A, 0x46, 0x49}, "image/jpeg"},
+		{"GIF", []byte{0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x00, 0x00, 0x00}, "image/gif"},
+		{"BMP", []byte{0x42, 0x4D, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}, "image/bmp"},
+		{"WebP", []byte{0x52, 0x49, 0x46, 0x46, 0x00, 0x00, 0x00, 0x00, 0x57, 0x45, 0x42, 0x50}, "image/webp"},
+		{"TIFF-LE", []byte{0x49, 0x49, 0x2A, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}, "image/tiff"},
+		{"TIFF-BE", []byte{0x4D, 0x4D, 0x00, 0x2A, 0x00, 0x00, 0x00, 0x00, 0x00}, "image/tiff"},
+		{"unknown", []byte{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08}, ""},
+		{"too short", []byte{0x89, 0x50}, ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := clipboard.DetectMediaType(tt.data)
+			if got != tt.expected {
+				t.Errorf("DetectMediaType() = %q, want %q", got, tt.expected)
+			}
+		})
+	}
+}

internal/clipboard/clipboard_linux.go

@@ -0,0 +1,57 @@
+//go:build linux
+
+package clipboard
+
+import (
+	"os/exec"
+)
+
+// ReadImage reads image data from the system clipboard on Linux.
+// It tries xclip first (X11), then falls back to wl-paste (Wayland).
+func ReadImage() (*ImageData, error) {
+	// Try xclip first (X11).
+	if path, err := exec.LookPath("xclip"); err == nil {
+		data, err := readWithXclip(path)
+		if err == nil && len(data) > 0 {
+			mediaType := DetectMediaType(data)
+			if mediaType == "" {
+				mediaType = "image/png" // xclip was asked for image/png
+			}
+			return &ImageData{Data: data, MediaType: mediaType}, nil
+		}
+	}
+
+	// Fallback to wl-paste (Wayland).
+	if path, err := exec.LookPath("wl-paste"); err == nil {
+		data, err := readWithWlPaste(path)
+		if err == nil && len(data) > 0 {
+			mediaType := DetectMediaType(data)
+			if mediaType == "" {
+				mediaType = "image/png"
+			}
+			return &ImageData{Data: data, MediaType: mediaType}, nil
+		}
+	}
+
+	// Check if either tool exists but just had no image.
+	if _, err := exec.LookPath("xclip"); err == nil {
+		return nil, ErrNoImage
+	}
+	if _, err := exec.LookPath("wl-paste"); err == nil {
+		return nil, ErrNoImage
+	}
+
+	return nil, errNoClipboardTool
+}
+
+// readWithXclip reads image data using xclip.
+func readWithXclip(xclipPath string) ([]byte, error) {
+	cmd := exec.Command(xclipPath, "-selection", "clipboard", "-t", "image/png", "-o")
+	return cmd.Output()
+}
+
+// readWithWlPaste reads image data using wl-paste.
+func readWithWlPaste(wlPastePath string) ([]byte, error) {
+	cmd := exec.Command(wlPastePath, "--type", "image/png")
+	return cmd.Output()
+}

internal/clipboard/clipboard_windows.go

@@ -0,0 +1,9 @@
+//go:build windows
+
+package clipboard
+
+// ReadImage reads image data from the system clipboard on Windows.
+// Windows clipboard image support is not yet implemented.
+func ReadImage() (*ImageData, error) {
+	return nil, errNoClipboardTool
+}

internal/compaction/compaction.go

@@ -1,14 +1,22 @@
 // Package compaction provides context window management with token estimation,
 // compaction triggers, and LLM-based conversation summarization.
 //
-// The algorithm mirrors Pi's approach: preserve a token budget of recent
+// The algorithm preserves a token budget of recent
 // messages (KeepRecentTokens, default 20 000) rather than a fixed message
 // count. Auto-compaction fires when estimated context usage exceeds
 // contextWindow − ReserveTokens.
+//
+// Features modelled after pi's compaction system:
+//   - Tool result truncation (2000 char max) during serialisation
+//   - Split turn handling: when a single turn exceeds the keep budget,
+//     the turn prefix is summarised separately and merged
+//   - Cumulative file tracking: read and modified files extracted from
+//     tool calls and carried forward across compactions
 package compaction
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"strings"
 
@@ -19,8 +27,8 @@ import (
 // Token estimation
 // ---------------------------------------------------------------------------
 
-// EstimateTokens provides a rough token count (~4 chars per token).
-func EstimateTokens(text string) int {
+// estimateTokens provides a rough token count (~4 chars per token).
+func estimateTokens(text string) int {
 	return len(text) / 4
 }
 
@@ -40,7 +48,7 @@ func estimateSingleMessageTokens(msg fantasy.Message) int {
 	total := 0
 	for _, part := range msg.Content {
 		if tp, ok := part.(fantasy.TextPart); ok {
-			total += EstimateTokens(tp.Text)
+			total += estimateTokens(tp.Text)
 		}
 	}
 	return total
@@ -50,8 +58,8 @@ func estimateSingleMessageTokens(msg fantasy.Message) int {
 // Auto-compact trigger
 // ---------------------------------------------------------------------------
 
-// ShouldCompact reports whether auto-compaction should fire. It uses Pi's
-// formula: contextTokens > contextWindow − reserveTokens.
+// ShouldCompact reports whether auto-compaction should fire.
+// Formula: contextTokens > contextWindow − reserveTokens.
 func ShouldCompact(messages []fantasy.Message, contextWindow int, reserveTokens int) bool {
 	if contextWindow <= 0 || reserveTokens <= 0 {
 		return false
@@ -66,14 +74,17 @@ func ShouldCompact(messages []fantasy.Message, contextWindow int, reserveTokens
 
 // CompactionResult contains statistics from a compaction operation.
 type CompactionResult struct {
-	Summary         string // LLM-generated summary of compacted messages
-	OriginalTokens  int    // Estimated token count before compaction
-	CompactedTokens int    // Estimated token count after compaction
-	MessagesRemoved int    // Number of messages replaced by the summary
+	Summary         string   // LLM-generated summary of compacted messages
+	OriginalTokens  int      // Estimated token count before compaction
+	CompactedTokens int      // Estimated token count after compaction
+	MessagesRemoved int      // Number of messages replaced by the summary
+	CutPoint        int      // Index in the original messages where the cut was made
+	ReadFiles       []string // Files read during the compacted conversation
+	ModifiedFiles   []string // Files modified during the compacted conversation
 }
 
-// CompactionOptions configures compaction behaviour. Pi-style token-based
-// defaults are applied for zero-value fields.
+// CompactionOptions configures compaction behaviour. Token-based defaults
+// are applied for zero-value fields.
 type CompactionOptions struct {
 	ContextWindow    int    // Model's context window size (tokens)
 	ReserveTokens    int    // Tokens to reserve for LLM response, default 16384
@@ -81,7 +92,7 @@ type CompactionOptions struct {
 	SummaryPrompt    string // Custom summary prompt (empty = use default)
 }
 
-// defaults fills zero-value fields with sensible Pi-style defaults.
+// defaults fills zero-value fields with sensible defaults.
 func (o *CompactionOptions) defaults() {
 	if o.ReserveTokens <= 0 {
 		o.ReserveTokens = 16384
@@ -92,13 +103,13 @@ func (o *CompactionOptions) defaults() {
 }
 
 // defaultSystemPrompt is the system prompt sent to the summarisation LLM.
-// Matches Pi's compaction system prompt.
+
 const defaultSystemPrompt = `You are a context summarization assistant. Your task is to read a conversation between a user and an AI coding assistant, then produce a structured summary following the exact format specified.
 
 Do NOT continue the conversation. Do NOT respond to any questions in the conversation. ONLY output the structured summary.`
 
 // defaultSummaryPrompt is the user prompt appended after the serialised
-// conversation. Matches Pi's initial-compaction format.
+// conversation.
 const defaultSummaryPrompt = `The messages above are a conversation to summarize. Create a structured context checkpoint summary that another LLM will use to continue the work.
 
 Use this EXACT format:
@@ -130,10 +141,36 @@ Use this EXACT format:
 - [Any data, examples, or references needed to continue]
 - [Or "(none)" if not applicable]
 
+<read-files>
+[One file path per line for files that were read during the conversation]
+</read-files>
+
+<modified-files>
+[One file path per line for files that were created, edited, or written during the conversation]
+</modified-files>
+
 Keep each section concise. Preserve exact file paths, function names, and error messages.`
 
 // ---------------------------------------------------------------------------
-// Cut point (token-based, Pi-style)
+// Tool result truncation
+// ---------------------------------------------------------------------------
+
+// maxToolResultChars is the maximum length of tool result text preserved
+// during serialisation. Longer results are truncated with a marker.
+const maxToolResultChars = 2000
+
+// truncateToolResult truncates text to maxToolResultChars, appending a
+// marker indicating how many characters were removed.
+func truncateToolResult(text string) string {
+	if len(text) <= maxToolResultChars {
+		return text
+	}
+	truncated := len(text) - maxToolResultChars
+	return text[:maxToolResultChars] + fmt.Sprintf("\n[...%d chars truncated]", truncated)
+}
+
+// ---------------------------------------------------------------------------
+// Cut point (token-based)
 // ---------------------------------------------------------------------------
 
 // isValidCutPoint returns true if the message at index i is a valid place to
@@ -143,11 +180,26 @@ func isValidCutPoint(msg fantasy.Message) bool {
 	return msg.Role != fantasy.MessageRoleTool
 }
 
+// findTurnStart returns the index of the user message that starts the turn
+// containing messages[idx]. A "turn" starts with a user message and includes
+// all subsequent assistant/tool messages until the next user message.
+func findTurnStart(messages []fantasy.Message, idx int) int {
+	for i := idx; i >= 0; i-- {
+		if messages[i].Role == fantasy.MessageRoleUser {
+			return i
+		}
+	}
+	return 0
+}
+
 // FindCutPoint walks backward from the end of messages, accumulating tokens
 // until the keepRecentTokens budget is filled. Returns the index that
 // separates "old" messages (0..cutPoint-1, to be summarised) from "recent"
 // messages (cutPoint..end, to be preserved).
 //
+// The cut point prefers turn boundaries (user messages). When a single turn
+// exceeds the budget, the cut lands mid-turn (IsSplitTurn returns true).
+//
 // Returns 0 if there are fewer than 2 messages or all messages fit within
 // the keep budget.
 func FindCutPoint(messages []fantasy.Message, keepRecentTokens int) int {
@@ -193,6 +245,23 @@ func FindCutPoint(messages []fantasy.Message, keepRecentTokens int) int {
 	return 0
 }
 
+// IsSplitTurn returns true if the cut point lands in the middle of a turn
+// (i.e. the message at cutPoint is not a user message, meaning we're
+// splitting a single turn's assistant/tool messages).
+func IsSplitTurn(messages []fantasy.Message, cutPoint int) bool {
+	if cutPoint <= 0 || cutPoint >= len(messages) {
+		return false
+	}
+	// If the cut point is at a user message, it's a clean turn boundary.
+	if messages[cutPoint].Role == fantasy.MessageRoleUser {
+		return false
+	}
+	// Otherwise we're cutting mid-turn — check if the turn started before
+	// the cut point.
+	turnStart := findTurnStart(messages, cutPoint)
+	return turnStart < cutPoint
+}
+
 // forceCutPoint returns a cut point that keeps only the last non-tool
 // message, summarising everything before it. Used when the budget-based
 // FindCutPoint returns 0 but the caller wants to compact anyway (manual
@@ -208,11 +277,103 @@ func forceCutPoint(messages []fantasy.Message) int {
 }
 
 // ---------------------------------------------------------------------------
-// Message serialisation (Pi-style)
+// File tracking
 // ---------------------------------------------------------------------------
 
-// roleLabel returns a human-readable label for a fantasy message role,
-// matching Pi's serialisation format.
+// fileOps contains cumulative file operation tracking.
+type fileOps struct {
+	ReadFiles     map[string]bool
+	ModifiedFiles map[string]bool
+}
+
+func newFileOps() *fileOps {
+	return &fileOps{
+		ReadFiles:     make(map[string]bool),
+		ModifiedFiles: make(map[string]bool),
+	}
+}
+
+// extractFileOps scans messages for tool calls and extracts file paths.
+// It recognises the built-in Kit tools: read, write, edit, bash, grep, find, ls.
+func extractFileOps(messages []fantasy.Message) *fileOps {
+	ops := newFileOps()
+	for _, msg := range messages {
+		for _, part := range msg.Content {
+			tc, ok := part.(fantasy.ToolCallPart)
+			if !ok {
+				continue
+			}
+
+			// Parse the JSON input to extract path arguments.
+			var args map[string]any
+			if err := json.Unmarshal([]byte(tc.Input), &args); err != nil {
+				continue
+			}
+
+			path, _ := args["path"].(string)
+			if path == "" {
+				continue
+			}
+
+			switch tc.ToolName {
+			case "read", "grep", "find", "ls":
+				ops.ReadFiles[path] = true
+			case "write", "edit":
+				ops.ModifiedFiles[path] = true
+			}
+		}
+	}
+	return ops
+}
+
+// merge combines another fileOps into this one (for cumulative tracking).
+func (f *fileOps) merge(other *fileOps) {
+	if other == nil {
+		return
+	}
+	for k := range other.ReadFiles {
+		f.ReadFiles[k] = true
+	}
+	for k := range other.ModifiedFiles {
+		f.ModifiedFiles[k] = true
+	}
+}
+
+// mergeSlices adds previously tracked file lists (from a prior compaction).
+func (f *fileOps) mergeSlices(readFiles, modifiedFiles []string) {
+	for _, p := range readFiles {
+		f.ReadFiles[p] = true
+	}
+	for _, p := range modifiedFiles {
+		f.ModifiedFiles[p] = true
+	}
+}
+
+// sortedKeys returns the keys of a bool map sorted alphabetically.
+func sortedKeys(m map[string]bool) []string {
+	if len(m) == 0 {
+		return nil
+	}
+	keys := make([]string, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	// Simple sort — no need for sort package for small lists.
+	for i := 0; i < len(keys); i++ {
+		for j := i + 1; j < len(keys); j++ {
+			if keys[j] < keys[i] {
+				keys[i], keys[j] = keys[j], keys[i]
+			}
+		}
+	}
+	return keys
+}
+
+// ---------------------------------------------------------------------------
+// Message serialisation
+// ---------------------------------------------------------------------------
+
+// roleLabel returns a human-readable label for a fantasy message role.
 func roleLabel(role fantasy.MessageRole) string {
 	switch role {
 	case fantasy.MessageRoleUser:
@@ -229,16 +390,26 @@ func roleLabel(role fantasy.MessageRole) string {
 }
 
 // serializeMessages converts a slice of fantasy messages into a plain-text
-// representation suitable for sending to the summarisation LLM. The format
-// mirrors Pi's compaction serialisation.
+// representation suitable for sending to the summarisation LLM. Tool result
+// text is truncated to maxToolResultChars to keep the summarisation request
+// within reasonable token budgets.
 func serializeMessages(messages []fantasy.Message) string {
 	var sb strings.Builder
 	for _, msg := range messages {
 		sb.WriteString(roleLabel(msg.Role))
 		sb.WriteString(":\n")
 		for _, part := range msg.Content {
-			if tp, ok := part.(fantasy.TextPart); ok {
-				sb.WriteString(tp.Text)
+			switch p := part.(type) {
+			case fantasy.TextPart:
+				if msg.Role == fantasy.MessageRoleTool {
+					sb.WriteString(truncateToolResult(p.Text))
+				} else {
+					sb.WriteString(p.Text)
+				}
+			case fantasy.ToolCallPart:
+				fmt.Fprintf(&sb, "[Tool call: %s(%s)]", p.ToolName, truncateToolResult(p.Input))
+			case fantasy.ReasoningPart:
+				fmt.Fprintf(&sb, "[Thinking]: %s", truncateToolResult(p.Text))
 			}
 		}
 		sb.WriteString("\n\n")
@@ -250,6 +421,13 @@ func serializeMessages(messages []fantasy.Message) string {
 // Compact
 // ---------------------------------------------------------------------------
 
+// PreviousCompaction carries file tracking state from a prior compaction so
+// that file operations accumulate across multiple compactions.
+type PreviousCompaction struct {
+	ReadFiles     []string
+	ModifiedFiles []string
+}
+
 // Compact summarises older messages using the LLM, returning the compaction
 // result and a new message slice (summary message + preserved recent
 // messages).
@@ -261,12 +439,16 @@ func serializeMessages(messages []fantasy.Message) string {
 // customInstructions is optional text appended to the summary prompt (e.g.
 // "Focus on the API design decisions"). Pass "" to use the default prompt
 // only.
+//
+// prev carries file tracking from a previous compaction for cumulative
+// tracking. Pass nil if there is no prior compaction.
 func Compact(
 	ctx context.Context,
 	model fantasy.LanguageModel,
 	messages []fantasy.Message,
 	opts CompactionOptions,
 	customInstructions string,
+	prev *PreviousCompaction,
 ) (*CompactionResult, []fantasy.Message, error) {
 	opts.defaults()
 
@@ -277,8 +459,8 @@ func Compact(
 	cutPoint := FindCutPoint(messages, opts.KeepRecentTokens)
 	if cutPoint == 0 {
 		// All messages fit within the keep budget. Force a cut that
-		// keeps only the last non-tool message — matching Pi, which
-		// always compacts when the user explicitly requests it.
+		// keeps only the last non-tool message — always compact when
+		// the user explicitly requests it.
 		cutPoint = forceCutPoint(messages)
 		if cutPoint == 0 {
 			return nil, messages, nil
@@ -289,30 +471,30 @@ func Compact(
 	recentMessages := messages[cutPoint:]
 	originalTokens := EstimateMessageTokens(messages)
 
-	// Serialise old messages to text, matching Pi's format.
-	conversationText := serializeMessages(oldMessages)
-
-	// Build the user-facing prompt: conversation text + summary instructions.
-	userPrompt := opts.SummaryPrompt
-	if userPrompt == "" {
-		userPrompt = defaultSummaryPrompt
-	}
-	if customInstructions != "" {
-		userPrompt += "\n\nAdditional instructions: " + customInstructions
+	// Extract file operations from old messages.
+	ops := extractFileOps(oldMessages)
+	// Accumulate from previous compaction if present.
+	if prev != nil {
+		ops.mergeSlices(prev.ReadFiles, prev.ModifiedFiles)
 	}
+	// Also scan recent messages for file ops (they'll be carried forward).
+	recentOps := extractFileOps(recentMessages)
+	ops.merge(recentOps)
 
-	// Create a lightweight agent (no tools) just for summarisation.
-	summaryAgent := fantasy.NewAgent(model,
-		fantasy.WithSystemPrompt(defaultSystemPrompt),
-	)
-	result, err := summaryAgent.Generate(ctx, fantasy.AgentCall{
-		Prompt: conversationText + "\n\n" + userPrompt,
-	})
+	// Handle split turns: when the cut lands mid-turn, summarise the turn
+	// prefix separately and merge with the history summary.
+	var summaryText string
+	var err error
+
+	if IsSplitTurn(messages, cutPoint) {
+		summaryText, err = compactSplitTurn(ctx, model, oldMessages, messages, cutPoint, opts, customInstructions)
+	} else {
+		summaryText, err = compactNormal(ctx, model, oldMessages, opts, customInstructions)
+	}
 	if err != nil {
-		return nil, nil, fmt.Errorf("compaction summarisation failed: %w", err)
+		return nil, nil, err
 	}
 
-	summaryText := result.Response.Content.Text()
 	if summaryText == "" {
 		return nil, nil, fmt.Errorf("compaction produced an empty summary")
 	}
@@ -338,5 +520,120 @@ func Compact(
 		OriginalTokens:  originalTokens,
 		CompactedTokens: compactedTokens,
 		MessagesRemoved: len(oldMessages),
+		CutPoint:        cutPoint,
+		ReadFiles:       sortedKeys(ops.ReadFiles),
+		ModifiedFiles:   sortedKeys(ops.ModifiedFiles),
 	}, newMessages, nil
 }
+
+// compactNormal generates a summary for a clean turn-boundary cut.
+func compactNormal(
+	ctx context.Context,
+	model fantasy.LanguageModel,
+	oldMessages []fantasy.Message,
+	opts CompactionOptions,
+	customInstructions string,
+) (string, error) {
+	conversationText := serializeMessages(oldMessages)
+	return generateSummary(ctx, model, conversationText, opts, customInstructions)
+}
+
+// compactSplitTurn handles the case where the cut point lands mid-turn.
+// It generates two summaries and merges them:
+//  1. History summary: all complete turns before the split turn
+//  2. Turn prefix summary: the early part of the split turn (from the turn's
+//     user message up to the cut point)
+//
+// The merged result preserves context from both the older history and the
+// beginning of the current long turn.
+func compactSplitTurn(
+	ctx context.Context,
+	model fantasy.LanguageModel,
+	oldMessages []fantasy.Message,
+	allMessages []fantasy.Message,
+	cutPoint int,
+	opts CompactionOptions,
+	customInstructions string,
+) (string, error) {
+	// Find where the split turn starts.
+	turnStart := findTurnStart(allMessages, cutPoint)
+
+	// Messages before the turn are the "history" portion.
+	historyMessages := oldMessages
+	if turnStart > 0 && turnStart < len(oldMessages) {
+		historyMessages = oldMessages[:turnStart]
+	}
+
+	// The turn prefix: from turnStart to cutPoint.
+	turnPrefixMessages := allMessages[turnStart:cutPoint]
+
+	var historySummary string
+	var err error
+
+	// Generate history summary if there are complete turns before the split.
+	if len(historyMessages) >= 2 {
+		historySummary, err = generateSummary(ctx, model,
+			serializeMessages(historyMessages), opts, "")
+		if err != nil {
+			return "", fmt.Errorf("split turn history summary failed: %w", err)
+		}
+	}
+
+	// Generate turn prefix summary.
+	turnPrefixText := serializeMessages(turnPrefixMessages)
+	turnPrefixPrompt := "The messages above are the BEGINNING of a long turn that was split. " +
+		"Summarize the work done so far in this turn, preserving tool call results, " +
+		"file changes, and progress. Another LLM will continue this turn."
+	if customInstructions != "" {
+		turnPrefixPrompt += "\n\nAdditional instructions: " + customInstructions
+	}
+
+	summaryAgent := fantasy.NewAgent(model,
+		fantasy.WithSystemPrompt(defaultSystemPrompt),
+	)
+	result, err := summaryAgent.Generate(ctx, fantasy.AgentCall{
+		Prompt: turnPrefixText + "\n\n" + turnPrefixPrompt,
+	})
+	if err != nil {
+		return "", fmt.Errorf("split turn prefix summary failed: %w", err)
+	}
+	turnPrefixSummary := result.Response.Content.Text()
+
+	// Merge the two summaries.
+	if historySummary != "" && turnPrefixSummary != "" {
+		return historySummary + "\n\n---\n\n## Current Turn (in progress)\n\n" + turnPrefixSummary, nil
+	}
+	if turnPrefixSummary != "" {
+		return turnPrefixSummary, nil
+	}
+	return historySummary, nil
+}
+
+// generateSummary calls the LLM to produce a structured summary.
+func generateSummary(
+	ctx context.Context,
+	model fantasy.LanguageModel,
+	conversationText string,
+	opts CompactionOptions,
+	customInstructions string,
+) (string, error) {
+	userPrompt := opts.SummaryPrompt
+	if userPrompt == "" {
+		userPrompt = defaultSummaryPrompt
+	}
+	if customInstructions != "" {
+		userPrompt += "\n\nAdditional instructions: " + customInstructions
+	}
+
+	summaryAgent := fantasy.NewAgent(model,
+		fantasy.WithSystemPrompt(defaultSystemPrompt),
+	)
+	result, err := summaryAgent.Generate(ctx, fantasy.AgentCall{
+		Prompt: conversationText + "\n\n" + userPrompt,
+	})
+	if err != nil {
+		return "", fmt.Errorf("compaction summarisation failed: %w", err)
+	}
+
+	return result.Response.Content.Text(), nil
+}

internal/compaction/compaction_test.go

@@ -36,9 +36,9 @@ func TestEstimateTokens(t *testing.T) {
 		{"hello world", 2}, // 11 / 4 = 2
 	}
 	for _, tt := range tests {
-		got := EstimateTokens(tt.text)
+		got := estimateTokens(tt.text)
 		if got != tt.want {
-			t.Errorf("EstimateTokens(%q) = %d, want %d", tt.text, got, tt.want)
+			t.Errorf("estimateTokens(%q) = %d, want %d", tt.text, got, tt.want)
 		}
 	}
 }
@@ -63,7 +63,7 @@ func TestEstimateMessageTokens_Empty(t *testing.T) {
 }
 
 // ---------------------------------------------------------------------------
-// ShouldCompact (Pi-style: contextTokens > contextWindow - reserveTokens)
+// ShouldCompact (contextTokens > contextWindow - reserveTokens)
 // ---------------------------------------------------------------------------
 
 func TestShouldCompact(t *testing.T) {
@@ -94,7 +94,7 @@ func TestShouldCompact(t *testing.T) {
 }
 
 // ---------------------------------------------------------------------------
-// FindCutPoint (token-based, Pi-style)
+// FindCutPoint (token-based)
 // ---------------------------------------------------------------------------
 
 func TestFindCutPoint_TokenBased(t *testing.T) {
@@ -243,7 +243,7 @@ func TestCompact_TooFewMessages(t *testing.T) {
 		makeTextMessageN(fantasy.MessageRoleUser, 400),
 	}
 
-	result, newMsgs, err := Compact(context.TODO(), nil, msgs, CompactionOptions{}, "")
+	result, newMsgs, err := Compact(context.TODO(), nil, msgs, CompactionOptions{}, "", nil)
 	if err != nil {
 		t.Fatalf("unexpected error: %v", err)
 	}
@@ -262,7 +262,7 @@ func TestCompact_WithinBudget(t *testing.T) {
 		makeTextMessageN(fantasy.MessageRoleAssistant, 400),
 	}
 
-	result, newMsgs, err := Compact(context.TODO(), nil, msgs, CompactionOptions{}, "")
+	result, newMsgs, err := Compact(context.TODO(), nil, msgs, CompactionOptions{}, "", nil)
 	if err != nil {
 		t.Fatalf("unexpected error: %v", err)
 	}
@@ -273,3 +273,169 @@ func TestCompact_WithinBudget(t *testing.T) {
 		t.Errorf("messages changed: got %d, want %d", len(newMsgs), len(msgs))
 	}
 }
+
+// ---------------------------------------------------------------------------
+// Tool result truncation
+// ---------------------------------------------------------------------------
+
+func TestTruncateToolResult(t *testing.T) {
+	// Short text — no truncation.
+	short := strings.Repeat("x", 100)
+	if got := truncateToolResult(short); got != short {
+		t.Errorf("truncated short text unexpectedly")
+	}
+
+	// Exactly at limit.
+	exact := strings.Repeat("x", maxToolResultChars)
+	if got := truncateToolResult(exact); got != exact {
+		t.Errorf("truncated text at exact limit")
+	}
+
+	// Over limit.
+	over := strings.Repeat("x", maxToolResultChars+500)
+	got := truncateToolResult(over)
+	if len(got) > maxToolResultChars+50 { // allow room for marker
+		t.Errorf("truncated text too long: %d chars", len(got))
+	}
+	if !strings.Contains(got, "500 chars truncated") {
+		t.Errorf("truncation marker missing, got: %s", got[maxToolResultChars:])
+	}
+}
+
+func TestSerializeMessages_TruncatesToolResults(t *testing.T) {
+	longResult := strings.Repeat("R", maxToolResultChars+1000)
+	msgs := []fantasy.Message{
+		makeTextMessage(fantasy.MessageRoleUser, "question"),
+		{
+			Role:    fantasy.MessageRoleTool,
+			Content: []fantasy.MessagePart{fantasy.TextPart{Text: longResult}},
+		},
+	}
+
+	serialized := serializeMessages(msgs)
+	if strings.Contains(serialized, longResult) {
+		t.Error("tool result was not truncated during serialisation")
+	}
+	if !strings.Contains(serialized, "chars truncated") {
+		t.Error("truncation marker missing in serialised output")
+	}
+}
+
+func TestSerializeMessages_PreservesNonToolText(t *testing.T) {
+	longText := strings.Repeat("T", maxToolResultChars+1000)
+	msgs := []fantasy.Message{
+		makeTextMessage(fantasy.MessageRoleUser, longText),
+	}
+
+	serialized := serializeMessages(msgs)
+	if !strings.Contains(serialized, longText) {
+		t.Error("non-tool text was unexpectedly truncated")
+	}
+}
+
+// ---------------------------------------------------------------------------
+// Split turn detection
+// ---------------------------------------------------------------------------
+
+func TestIsSplitTurn(t *testing.T) {
+	msgs := []fantasy.Message{
+		makeTextMessageN(fantasy.MessageRoleUser, 400),      // 0: turn 1 user
+		makeTextMessageN(fantasy.MessageRoleAssistant, 400), // 1: turn 1 assistant
+		makeTextMessageN(fantasy.MessageRoleUser, 400),      // 2: turn 2 user
+		makeTextMessageN(fantasy.MessageRoleAssistant, 400), // 3: turn 2 assistant
+		makeTextMessageN(fantasy.MessageRoleTool, 400),      // 4: turn 2 tool result
+		makeTextMessageN(fantasy.MessageRoleAssistant, 400), // 5: turn 2 assistant
+	}
+
+	tests := []struct {
+		name     string
+		cutPoint int
+		want     bool
+	}{
+		{"at user message (turn boundary)", 2, false},
+		{"at assistant mid-turn", 3, true},
+		{"at assistant after tool (mid-turn)", 5, true},
+		{"at 0 (no cut)", 0, false},
+		{"beyond range", 10, false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := IsSplitTurn(msgs, tt.cutPoint)
+			if got != tt.want {
+				t.Errorf("IsSplitTurn(msgs, %d) = %v, want %v", tt.cutPoint, got, tt.want)
+			}
+		})
+	}
+}
+
+// ---------------------------------------------------------------------------
+// File operations extraction
+// ---------------------------------------------------------------------------
+
+func TestExtractFileOps(t *testing.T) {
+	// Create messages with tool calls.
+	msgs := []fantasy.Message{
+		{
+			Role: fantasy.MessageRoleAssistant,
+			Content: []fantasy.MessagePart{
+				fantasy.ToolCallPart{ToolCallID: "1", ToolName: "read", Input: `{"path":"src/main.go"}`},
+				fantasy.ToolCallPart{ToolCallID: "2", ToolName: "write", Input: `{"path":"src/out.go"}`},
+				fantasy.ToolCallPart{ToolCallID: "3", ToolName: "edit", Input: `{"path":"src/edit.go"}`},
+				fantasy.ToolCallPart{ToolCallID: "4", ToolName: "grep", Input: `{"path":"src/search"}`},
+			},
+		},
+	}
+
+	ops := extractFileOps(msgs)
+	if !ops.ReadFiles["src/main.go"] {
+		t.Error("read file not tracked: src/main.go")
+	}
+	if !ops.ReadFiles["src/search"] {
+		t.Error("grep path not tracked as read: src/search")
+	}
+	if !ops.ModifiedFiles["src/out.go"] {
+		t.Error("write file not tracked: src/out.go")
+	}
+	if !ops.ModifiedFiles["src/edit.go"] {
+		t.Error("edit file not tracked: src/edit.go")
+	}
+}
+
+func TestFileOps_MergeSlices(t *testing.T) {
+	ops := newFileOps()
+	ops.ReadFiles["a.go"] = true
+	ops.ModifiedFiles["b.go"] = true
+
+	ops.mergeSlices(
+		[]string{"c.go", "a.go"},
+		[]string{"d.go"},
+	)
+
+	if len(ops.ReadFiles) != 2 { // a.go, c.go
+		t.Errorf("ReadFiles len = %d, want 2", len(ops.ReadFiles))
+	}
+	if len(ops.ModifiedFiles) != 2 { // b.go, d.go
+		t.Errorf("ModifiedFiles len = %d, want 2", len(ops.ModifiedFiles))
+	}
+}
+
+func TestSortedKeys(t *testing.T) {
+	m := map[string]bool{"c": true, "a": true, "b": true}
+	got := sortedKeys(m)
+	want := []string{"a", "b", "c"}
+	if len(got) != len(want) {
+		t.Fatalf("sortedKeys len = %d, want %d", len(got), len(want))
+	}
+	for i, v := range got {
+		if v != want[i] {
+			t.Errorf("sortedKeys[%d] = %q, want %q", i, v, want[i])
+		}
+	}
+}
+
+func TestSortedKeys_Empty(t *testing.T) {
+	got := sortedKeys(nil)
+	if got != nil {
+		t.Errorf("sortedKeys(nil) = %v, want nil", got)
+	}
+}

internal/config/config.go

@@ -105,42 +105,82 @@ type AdaptiveColor struct {
 	Dark  string `json:"dark,omitempty" yaml:"dark,omitempty"`
 }
 
+// MarkdownThemeConfig defines color overrides for markdown rendering and
+// syntax highlighting.
+type MarkdownThemeConfig struct {
+	Text    AdaptiveColor `json:"text,omitzero" yaml:"text,omitempty"`
+	Muted   AdaptiveColor `json:"muted,omitzero" yaml:"muted,omitempty"`
+	Heading AdaptiveColor `json:"heading,omitzero" yaml:"heading,omitempty"`
+	Emph    AdaptiveColor `json:"emph,omitzero" yaml:"emph,omitempty"`
+	Strong  AdaptiveColor `json:"strong,omitzero" yaml:"strong,omitempty"`
+	Link    AdaptiveColor `json:"link,omitzero" yaml:"link,omitempty"`
+	Code    AdaptiveColor `json:"code,omitzero" yaml:"code,omitempty"`
+	Error   AdaptiveColor `json:"error,omitzero" yaml:"error,omitempty"`
+	Keyword AdaptiveColor `json:"keyword,omitzero" yaml:"keyword,omitempty"`
+	String  AdaptiveColor `json:"string,omitzero" yaml:"string,omitempty"`
+	Number  AdaptiveColor `json:"number,omitzero" yaml:"number,omitempty"`
+	Comment AdaptiveColor `json:"comment,omitzero" yaml:"comment,omitempty"`
+}
+
 // Theme defines the color scheme for the application UI with adaptive colors
 // that support both light and dark modes.
 type Theme struct {
-	Primary     AdaptiveColor `json:"primary" yaml:"primary"`
-	Secondary   AdaptiveColor `json:"secondary" yaml:"secondary"`
-	Success     AdaptiveColor `json:"success" yaml:"success"`
-	Warning     AdaptiveColor `json:"warning" yaml:"warning"`
-	Error       AdaptiveColor `json:"error" yaml:"error"`
-	Info        AdaptiveColor `json:"info" yaml:"info"`
-	Text        AdaptiveColor `json:"text" yaml:"text"`
-	Muted       AdaptiveColor `json:"muted" yaml:"muted"`
-	VeryMuted   AdaptiveColor `json:"very-muted" yaml:"very-muted"`
-	Background  AdaptiveColor `json:"background" yaml:"background"`
-	Border      AdaptiveColor `json:"border" yaml:"border"`
-	MutedBorder AdaptiveColor `json:"muted-border" yaml:"muted-border"`
-	System      AdaptiveColor `json:"system" yaml:"system"`
-	Tool        AdaptiveColor `json:"tool" yaml:"tool"`
-	Accent      AdaptiveColor `json:"accent" yaml:"accent"`
-	Highlight   AdaptiveColor `json:"highlight" yaml:"highlight"`
+	Primary     AdaptiveColor `json:"primary,omitzero" yaml:"primary,omitempty"`
+	Secondary   AdaptiveColor `json:"secondary,omitzero" yaml:"secondary,omitempty"`
+	Success     AdaptiveColor `json:"success,omitzero" yaml:"success,omitempty"`
+	Warning     AdaptiveColor `json:"warning,omitzero" yaml:"warning,omitempty"`
+	Error       AdaptiveColor `json:"error,omitzero" yaml:"error,omitempty"`
+	Info        AdaptiveColor `json:"info,omitzero" yaml:"info,omitempty"`
+	Text        AdaptiveColor `json:"text,omitzero" yaml:"text,omitempty"`
+	Muted       AdaptiveColor `json:"muted,omitzero" yaml:"muted,omitempty"`
+	VeryMuted   AdaptiveColor `json:"very-muted,omitzero" yaml:"very-muted,omitempty"`
+	Background  AdaptiveColor `json:"background,omitzero" yaml:"background,omitempty"`
+	Border      AdaptiveColor `json:"border,omitzero" yaml:"border,omitempty"`
+	MutedBorder AdaptiveColor `json:"muted-border,omitzero" yaml:"muted-border,omitempty"`
+	System      AdaptiveColor `json:"system,omitzero" yaml:"system,omitempty"`
+	Tool        AdaptiveColor `json:"tool,omitzero" yaml:"tool,omitempty"`
+	Accent      AdaptiveColor `json:"accent,omitzero" yaml:"accent,omitempty"`
+	Highlight   AdaptiveColor `json:"highlight,omitzero" yaml:"highlight,omitempty"`
+
+	// Diff block backgrounds
+	DiffInsertBg  AdaptiveColor `json:"diff-insert-bg,omitzero" yaml:"diff-insert-bg,omitempty"`
+	DiffDeleteBg  AdaptiveColor `json:"diff-delete-bg,omitzero" yaml:"diff-delete-bg,omitempty"`
+	DiffEqualBg   AdaptiveColor `json:"diff-equal-bg,omitzero" yaml:"diff-equal-bg,omitempty"`
+	DiffMissingBg AdaptiveColor `json:"diff-missing-bg,omitzero" yaml:"diff-missing-bg,omitempty"`
+
+	// Code/output block backgrounds
+	CodeBg   AdaptiveColor `json:"code-bg,omitzero" yaml:"code-bg,omitempty"`
+	GutterBg AdaptiveColor `json:"gutter-bg,omitzero" yaml:"gutter-bg,omitempty"`
+	WriteBg  AdaptiveColor `json:"write-bg,omitzero" yaml:"write-bg,omitempty"`
+
+	// Markdown rendering and syntax highlighting
+	Markdown MarkdownThemeConfig `json:"markdown,omitzero" yaml:"markdown,omitempty"`
 }
 
-// MarkdownTheme defines the color scheme for markdown rendering with syntax
-// highlighting support and adaptive colors for light and dark modes.
-type MarkdownTheme struct {
-	Text    AdaptiveColor `json:"text" yaml:"text"`
-	Muted   AdaptiveColor `json:"muted" yaml:"muted"`
-	Heading AdaptiveColor `json:"heading" yaml:"heading"`
-	Emph    AdaptiveColor `json:"emph" yaml:"emph"`
-	Strong  AdaptiveColor `json:"strong" yaml:"strong"`
-	Link    AdaptiveColor `json:"link" yaml:"link"`
-	Code    AdaptiveColor `json:"code" yaml:"code"`
-	Error   AdaptiveColor `json:"error" yaml:"error"`
-	Keyword AdaptiveColor `json:"keyword" yaml:"keyword"`
-	String  AdaptiveColor `json:"string" yaml:"string"`
-	Number  AdaptiveColor `json:"number" yaml:"number"`
-	Comment AdaptiveColor `json:"comment" yaml:"comment"`
+// CustomModelConfig defines a custom model that can be used with custom/custom
+// or other custom/ prefixed models. These models are loaded from the config file
+// and merged into the custom provider in the model registry.
+type CustomModelConfig struct {
+	Name        string      `json:"name" yaml:"name"`
+	Family      string      `json:"family,omitempty" yaml:"family,omitempty"`
+	Attachment  bool        `json:"attachment,omitempty" yaml:"attachment,omitempty"`
+	Reasoning   bool        `json:"reasoning,omitempty" yaml:"reasoning,omitempty"`
+	Temperature bool        `json:"temperature,omitempty" yaml:"temperature,omitempty"`
+	Knowledge   string      `json:"knowledge,omitempty" yaml:"knowledge,omitempty"`
+	Cost        CostConfig  `json:"cost" yaml:"cost"`
+	Limit       LimitConfig `json:"limit" yaml:"limit"`
+}
+
+// CostConfig defines the pricing for a custom model.
+type CostConfig struct {
+	Input  float64 `json:"input" yaml:"input"`
+	Output float64 `json:"output" yaml:"output"`
+}
+
+// LimitConfig defines context and output limits for a custom model.
+type LimitConfig struct {
+	Context int `json:"context" yaml:"context"`
+	Output  int `json:"output" yaml:"output"`
 }
 
 // Config represents the complete application configuration including MCP servers,
@@ -157,7 +197,6 @@ type Config struct {
 	ProviderURL    string                     `json:"provider-url,omitempty" yaml:"provider-url,omitempty"`
 	Stream         *bool                      `json:"stream,omitempty" yaml:"stream,omitempty"`
 	Theme          any                        `json:"theme" yaml:"theme"`
-	MarkdownTheme  any                        `json:"markdown-theme" yaml:"markdown-theme"`
 	// Model generation parameters
 	MaxTokens     int      `json:"max-tokens,omitempty" yaml:"max-tokens,omitempty"`
 	Temperature   *float32 `json:"temperature,omitempty" yaml:"temperature,omitempty"`
@@ -165,8 +204,18 @@ type Config struct {
 	TopK          *int32   `json:"top-k,omitempty" yaml:"top-k,omitempty"`
 	StopSequences []string `json:"stop-sequences,omitempty" yaml:"stop-sequences,omitempty"`
 
+	// Thinking / extended reasoning
+	ThinkingLevel string `json:"thinking-level,omitempty" yaml:"thinking-level,omitempty"`
+
 	// TLS configuration
 	TLSSkipVerify bool `json:"tls-skip-verify,omitempty" yaml:"tls-skip-verify,omitempty"`
+
+	// Prompt templates configuration
+	Prompts           []string `json:"prompts,omitempty" yaml:"prompts,omitempty"`
+	NoPromptTemplates bool     `json:"no-prompt-templates,omitempty" yaml:"no-prompt-templates,omitempty"`
+
+	// Custom model definitions (under custom/ provider)
+	CustomModels map[string]CustomModelConfig `json:"customModels,omitempty" yaml:"customModels,omitempty"`
 }
 
 // GetTransportType returns the transport type for the server config, mapping
@@ -370,11 +419,10 @@ func FilepathOr[T any](key string, value *T) error {
 				fmt.Fprintf(os.Stderr, "%q", err)
 				os.Exit(1)
 			}
-			if filepath.Ext(absPath) == ".json" {
+			switch filepath.Ext(absPath) {
+			case ".json":
 				return json.Unmarshal(b, value)
-			}
-
-			if filepath.Ext(absPath) == ".yaml" {
+			case ".yaml", ".yml":
 				return yaml.Unmarshal(b, value)
 			}
 		}

internal/core/bash.go

@@ -1,16 +1,41 @@
 package core
 
 import (
-	"bytes"
+	"bufio"
 	"context"
 	"fmt"
+	"io"
+	"os"
 	"os/exec"
 	"strings"
+	"sync"
 	"time"
 
 	"charm.land/fantasy"
 )
 
+// ToolOutputCallback is the signature for streaming tool output.
+// It receives tool call ID, tool name, output chunk, and whether it's stderr.
+type ToolOutputCallback func(toolCallID, toolName, chunk string, isStderr bool)
+
+// contextKey is a custom type for context keys to avoid collisions.
+type contextKey string
+
+const toolOutputCallbackKey contextKey = "toolOutputCallback"
+
+// ContextWithToolOutputCallback returns a new context with the tool output callback set.
+func ContextWithToolOutputCallback(ctx context.Context, callback ToolOutputCallback) context.Context {
+	return context.WithValue(ctx, toolOutputCallbackKey, callback)
+}
+
+// toolOutputCallbackFromContext retrieves the tool output callback from context.
+func toolOutputCallbackFromContext(ctx context.Context) ToolOutputCallback {
+	if cb, ok := ctx.Value(toolOutputCallbackKey).(ToolOutputCallback); ok {
+		return cb
+	}
+	return nil
+}
+
 const defaultBashTimeout = 120 * time.Second
 const maxBashTimeout = 600 * time.Second
 
@@ -90,32 +115,165 @@ func executeBash(ctx context.Context, call fantasy.ToolCall, workDir string) (fa
 		cmd.Dir = workDir
 	}
 
-	var stdout, stderr bytes.Buffer
-	cmd.Stdout = &stdout
-	cmd.Stderr = &stderr
+	// Ensure SHELL is set to bash so child processes (e.g. tmux) use bash
+	// rather than the user's login shell (which may be nushell, fish, etc.).
+	bashPath, err := exec.LookPath("bash")
+	if err != nil {
+		bashPath = "/bin/bash"
+	}
+	cmd.Env = append(os.Environ(), "SHELL="+bashPath)
 
-	err := cmd.Run()
+	// Get the output callback if present (for streaming support)
+	outputCallback := toolOutputCallbackFromContext(ctx)
+
+	if outputCallback != nil {
+		// Streaming mode: use pipes to capture output as it arrives
+		return executeBashStreaming(cmdCtx, call, cmd, outputCallback)
+	}
+
+	// Non-streaming mode: collect all output at once (original behavior)
+	return executeBashBuffered(cmdCtx, call, cmd)
+}
+
+// executeBashBuffered collects all output before returning (original behavior).
+// It uses explicit pipes (not cmd.Stdout) so that cmd.WaitDelay can forcibly
+// close them when grandchild processes hold pipe handles open after the
+// direct child exits.
+func executeBashBuffered(cmdCtx context.Context, call fantasy.ToolCall, cmd *exec.Cmd) (fantasy.ToolResponse, error) {
+	stdoutPipe, err := cmd.StdoutPipe()
+	if err != nil {
+		return fantasy.NewTextErrorResponse("failed to create stdout pipe"), nil
+	}
+	stderrPipe, err := cmd.StderrPipe()
+	if err != nil {
+		return fantasy.NewTextErrorResponse("failed to create stderr pipe"), nil
+	}
+
+	if err := cmd.Start(); err != nil {
+		return fantasy.NewTextErrorResponse(fmt.Sprintf("failed to start command: %v", err)), nil
+	}
+
+	// Read pipes concurrently
+	var wg sync.WaitGroup
+	var stdout, stderr strings.Builder
+	var stdoutErr, stderrErr error
+
+	wg.Add(2)
+	go func() {
+		defer wg.Done()
+		_, stdoutErr = io.Copy(&stdout, stdoutPipe)
+	}()
+	go func() {
+		defer wg.Done()
+		_, stderrErr = io.Copy(&stderr, stderrPipe)
+	}()
+
+	// Wait for the process to exit first. cmd.WaitDelay ensures that if
+	// pipes remain open (held by grandchild processes), they'll be forcibly
+	// closed after the grace period, which unblocks the io.Copy goroutines.
+	waitErr := cmd.Wait()
+
+	// Wait for pipe readers to finish draining.
+	wg.Wait()
+
+	// Ignore pipe read errors caused by WaitDelay force-closing —
+	// we still have whatever was read before the close.
+	_ = stdoutErr
+	_ = stderrErr
+
+	exitCode := 0
+	if waitErr != nil {
+		if exitErr, ok := waitErr.(*exec.ExitError); ok {
+			exitCode = exitErr.ExitCode()
+		} else if cmdCtx.Err() == context.DeadlineExceeded {
+			return fantasy.NewTextErrorResponse("command timed out"), nil
+		}
+	}
+
+	return buildBashResponse(stdout.String(), stderr.String(), exitCode)
+}
+
+// executeBashStreaming streams output as it arrives via the callback.
+func executeBashStreaming(cmdCtx context.Context, call fantasy.ToolCall, cmd *exec.Cmd, outputCallback ToolOutputCallback) (fantasy.ToolResponse, error) {
+	stdoutPipe, err := cmd.StdoutPipe()
+	if err != nil {
+		return fantasy.NewTextErrorResponse("failed to create stdout pipe"), nil
+	}
+	stderrPipe, err := cmd.StderrPipe()
+	if err != nil {
+		return fantasy.NewTextErrorResponse("failed to create stderr pipe"), nil
+	}
+
+	// Start command execution
+	if err := cmd.Start(); err != nil {
+		return fantasy.NewTextErrorResponse(fmt.Sprintf("failed to start command: %v", err)), nil
+	}
+
+	// Stream stdout and stderr concurrently
+	var wg sync.WaitGroup
+	var mu sync.Mutex
+	var stdoutChunks, stderrChunks []string
+
+	streamOutput := func(reader io.Reader, isStderr bool) {
+		defer wg.Done()
+		scanner := bufio.NewScanner(reader)
+		// Use larger buffer for long lines
+		buf := make([]byte, 0, 64*1024)
+		scanner.Buffer(buf, 1024*1024)
+
+		for scanner.Scan() {
+			chunk := scanner.Text()
+			// Send chunk to UI
+			outputCallback(call.ID, "bash", chunk, isStderr)
+			// Collect for final result
+			mu.Lock()
+			if isStderr {
+				stderrChunks = append(stderrChunks, chunk)
+			} else {
+				stdoutChunks = append(stdoutChunks, chunk)
+			}
+			mu.Unlock()
+		}
+	}
+
+	wg.Add(2)
+	go streamOutput(stdoutPipe, false)
+	go streamOutput(stderrPipe, true)
+
+	// Wait for the process to exit. cmd.WaitDelay ensures that if pipes
+	// remain open (held by grandchild processes), they'll be forcibly closed
+	// after the grace period, which unblocks the scanners above.
+	err = cmd.Wait()
+
+	// Wait for the pipe readers to finish draining. This will complete
+	// quickly since cmd.Wait() (with WaitDelay) has already ensured
+	// the pipes are closed.
+	wg.Wait()
 
 	exitCode := 0
 	if err != nil {
 		if exitErr, ok := err.(*exec.ExitError); ok {
 			exitCode = exitErr.ExitCode()
 		} else if cmdCtx.Err() == context.DeadlineExceeded {
-			return fantasy.NewTextErrorResponse(fmt.Sprintf("command timed out after %v", timeout)), nil
+			return fantasy.NewTextErrorResponse("command timed out"), nil
 		}
 	}
 
-	// Build result
+	return buildBashResponse(strings.Join(stdoutChunks, "\n"), strings.Join(stderrChunks, "\n"), exitCode)
+}
+
+// buildBashResponse constructs the final tool response from stdout/stderr.
+func buildBashResponse(stdout, stderr string, exitCode int) (fantasy.ToolResponse, error) {
 	var result strings.Builder
-	if stdout.Len() > 0 {
-		result.WriteString(stdout.String())
+	if stdout != "" {
+		result.WriteString(stdout)
 	}
-	if stderr.Len() > 0 {
+	if stderr != "" {
 		if result.Len() > 0 {
 			result.WriteString("\n")
 		}
 		result.WriteString("STDERR:\n")
-		result.WriteString(stderr.String())
+		result.WriteString(stderr)
 	}
 	if exitCode != 0 {
 		if result.Len() > 0 {
@@ -130,7 +288,7 @@ func executeBash(ctx context.Context, call fantasy.ToolCall, workDir string) (fa
 	}
 
 	// Truncate from tail (keep last N lines, most relevant for bash)
-	tr := truncateTail(output, defaultMaxLines, defaultMaxBytes)
+	tr := TruncateTail(output, defaultMaxLines, defaultMaxBytes)
 
 	if exitCode != 0 {
 		return fantasy.NewTextErrorResponse(tr.Content), nil

internal/core/bash_test.go

@@ -0,0 +1,129 @@
+package core
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+	"time"
+
+	"charm.land/fantasy"
+)
+
+// helper to create a bash tool call with the given command and optional timeout.
+func bashCall(command string, timeout float64) fantasy.ToolCall {
+	args := map[string]any{"command": command}
+	if timeout > 0 {
+		args["timeout"] = timeout
+	}
+	input, _ := json.Marshal(args)
+	return fantasy.ToolCall{
+		ID:    "test-call",
+		Name:  "bash",
+		Input: string(input),
+	}
+}
+
+func TestBash_SimpleCommand(t *testing.T) {
+	resp, err := executeBash(context.Background(), bashCall("echo hello", 0), "")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if resp.IsError {
+		t.Fatalf("expected success, got error: %s", resp.Content)
+	}
+	if resp.Content != "hello\n" {
+		t.Errorf("expected 'hello\\n', got %q", resp.Content)
+	}
+}
+
+func TestBash_TimeoutKillsProcess(t *testing.T) {
+	start := time.Now()
+	resp, err := executeBash(context.Background(), bashCall("sleep 60", 2), "")
+	elapsed := time.Since(start)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !resp.IsError {
+		t.Fatal("expected error response for timed-out command")
+	}
+	if elapsed > 10*time.Second {
+		t.Errorf("command took %v, expected ~2s timeout", elapsed)
+	}
+}
+
+func TestBash_BackgroundProcessDoesNotHang(t *testing.T) {
+	// This command spawns a background sleep that would hold pipes open
+	// forever if we didn't have process group killing + WaitDelay.
+	start := time.Now()
+	resp, err := executeBash(context.Background(), bashCall("echo done; sleep 3600 &", 5), "")
+	elapsed := time.Since(start)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	// The foreground command (echo) should complete quickly
+	if elapsed > 5*time.Second {
+		t.Errorf("command took %v, should complete in <5s (background process should not block)", elapsed)
+	}
+	if resp.IsError {
+		t.Fatalf("expected success, got error: %s", resp.Content)
+	}
+}
+
+func TestBash_BackgroundProcessDoesNotHang_Streaming(t *testing.T) {
+	// Same test but in streaming mode (with output callback).
+	ctx := ContextWithToolOutputCallback(context.Background(), func(_, _, _ string, _ bool) {})
+	start := time.Now()
+	resp, err := executeBash(ctx, bashCall("echo streaming; sleep 3600 &", 5), "")
+	elapsed := time.Since(start)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if elapsed > 5*time.Second {
+		t.Errorf("streaming command took %v, should complete in <5s", elapsed)
+	}
+	if resp.IsError {
+		t.Fatalf("expected success, got error: %s", resp.Content)
+	}
+}
+
+func TestBash_ContextCancellation(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		_, _ = executeBash(ctx, bashCall("sleep 60", 0), "")
+	}()
+
+	// Cancel after a short delay
+	time.Sleep(500 * time.Millisecond)
+	cancel()
+
+	// Should return promptly after cancellation
+	select {
+	case <-done:
+		// success
+	case <-time.After(5 * time.Second):
+		t.Fatal("executeBash did not return after context cancellation")
+	}
+}
+
+func TestBash_BannedCommand(t *testing.T) {
+	resp, err := executeBash(context.Background(), bashCall("alias foo=bar", 0), "")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !resp.IsError {
+		t.Fatal("expected error for banned command")
+	}
+}
+
+func TestBash_EmptyCommand(t *testing.T) {
+	resp, err := executeBash(context.Background(), bashCall("", 0), "")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !resp.IsError {
+		t.Fatal("expected error for empty command")
+	}
+}

internal/core/edit.go

@@ -6,8 +6,11 @@ import (
 	"os"
 	"strings"
 	"unicode"
+	"unicode/utf8"
 
 	"charm.land/fantasy"
+
+	udiff "github.com/aymanbagabas/go-udiff"
 )
 
 type editArgs struct {
@@ -76,13 +79,15 @@ func executeEdit(ctx context.Context, call fantasy.ToolCall, workDir string) (fa
 	// If no exact match, try fuzzy matching
 	if count == 0 {
 		if idx, matchLen := fuzzyMatch(normalized, normalizedOld); idx >= 0 {
-			// Apply fuzzy match
+			// Apply fuzzy match — the matched text is the original content slice
+			matchedText := normalized[idx : idx+matchLen]
 			newContent := normalized[:idx] + args.NewText + normalized[idx+matchLen:]
 			if err := os.WriteFile(absPath, []byte(newContent), 0644); err != nil {
 				return fantasy.NewTextErrorResponse(fmt.Sprintf("failed to write file: %v", err)), nil
 			}
-			diff := generateDiff(absPath, normalized, newContent, idx)
-			return fantasy.NewTextResponse(fmt.Sprintf("Applied edit (fuzzy match) to %s\n%s", args.Path, diff)), nil
+			diff := generateDiff(absPath, normalized, newContent)
+			resp := fantasy.NewTextResponse(fmt.Sprintf("Applied edit (fuzzy match) to %s\n%s", args.Path, diff))
+			return fantasy.WithResponseMetadata(resp, editDiffMeta(absPath, matchedText, args.NewText)), nil
 		}
 		return fantasy.NewTextErrorResponse(fmt.Sprintf("old_text not found in %s", args.Path)), nil
 	}
@@ -98,108 +103,129 @@ func executeEdit(ctx context.Context, call fantasy.ToolCall, workDir string) (fa
 		return fantasy.NewTextErrorResponse(fmt.Sprintf("failed to write file: %v", err)), nil
 	}
 
-	idx := strings.Index(normalized, normalizedOld)
-	diff := generateDiff(absPath, normalized, newContent, idx)
-	return fantasy.NewTextResponse(fmt.Sprintf("Applied edit to %s\n%s", args.Path, diff)), nil
+	diff := generateDiff(absPath, normalized, newContent)
+	resp := fantasy.NewTextResponse(fmt.Sprintf("Applied edit to %s\n%s", args.Path, diff))
+	return fantasy.WithResponseMetadata(resp, editDiffMeta(absPath, normalizedOld, args.NewText)), nil
+}
+
+// editDiffMeta builds the structured metadata attached to edit tool responses.
+func editDiffMeta(path, oldText, newText string) map[string]any {
+	return map[string]any{
+		"file_diffs": []map[string]any{{
+			"path":      path,
+			"additions": strings.Count(newText, "\n") + 1,
+			"deletions": strings.Count(oldText, "\n") + 1,
+			"diff_blocks": []map[string]any{{
+				"old_text": oldText,
+				"new_text": newText,
+			}},
+		}},
+	}
 }
 
 // fuzzyMatch tries to find old_text with relaxed matching:
-// - Strips trailing whitespace per line
-// - Normalizes unicode quotes to ASCII
-// - Normalizes unicode dashes/spaces
-// Returns (index, matchLength) or (-1, 0) if not found.
+//   - Strips trailing whitespace per line
+//   - Normalizes unicode quotes to ASCII
+//   - Normalizes unicode dashes/spaces
+//
+// Returns (index, matchLength) in the original content, or (-1, 0) if not
+// found or ambiguous (multiple matches).
 func fuzzyMatch(content, search string) (int, int) {
-	normalizedContent := normalizeForFuzzy(content)
-	normalizedSearch := normalizeForFuzzy(search)
+	normContent, contentMap := normalizeWithMap(content)
+	normSearch := normalizeForFuzzy(search)
 
-	idx := strings.Index(normalizedContent, normalizedSearch)
+	if normSearch == "" {
+		return -1, 0
+	}
+
+	idx := strings.Index(normContent, normSearch)
 	if idx < 0 {
 		return -1, 0
 	}
 
-	// Map back to original content position
-	// Since normalization can change lengths, we need to find the
-	// corresponding region in the original content
-	origIdx := mapFuzzyIndex(content, normalizedContent, idx)
-	origEnd := mapFuzzyIndex(content, normalizedContent, idx+len(normalizedSearch))
+	// Reject ambiguous matches — if there are multiple fuzzy matches
+	// we can't safely pick one.
+	if strings.Count(normContent, normSearch) > 1 {
+		return -1, 0
+	}
 
-	return origIdx, origEnd - origIdx
+	// Map normalized byte positions back to original byte positions.
+	origStart := contentMap[idx]
+	endNorm := idx + len(normSearch)
+	var origEnd int
+	if endNorm >= len(normContent) {
+		origEnd = len(content)
+	} else {
+		origEnd = contentMap[endNorm]
+	}
+
+	return origStart, origEnd - origStart
 }
 
-func normalizeForFuzzy(s string) string {
-	// Strip trailing whitespace per line
+// normalizeWithMap normalizes s for fuzzy matching and returns both the
+// normalized string and a byte-position mapping where mapping[i] is the
+// original byte position corresponding to normalized byte position i.
+//
+// Normalization: trim trailing whitespace per line, replace unicode
+// quotes/dashes/spaces with their ASCII equivalents.
+func normalizeWithMap(s string) (string, []int) {
+	var result []byte
+	var mapping []int // mapping[i] = original byte position for result byte i
+
 	lines := strings.Split(s, "\n")
-	for i, line := range lines {
-		lines[i] = strings.TrimRightFunc(line, unicode.IsSpace)
-	}
-	result := strings.Join(lines, "\n")
-
-	// Normalize smart quotes
-	replacer := strings.NewReplacer(
-		"\u201c", "\"", // left double quote
-		"\u201d", "\"", // right double quote
-		"\u2018", "'", // left single quote
-		"\u2019", "'", // right single quote
-		"\u2013", "-", // en dash
-		"\u2014", "-", // em dash
-		"\u00a0", " ", // non-breaking space
-	)
-	return replacer.Replace(result)
-}
-
-func mapFuzzyIndex(original, normalized string, normIdx int) int {
-	// Simple approach: count runes up to normIdx in normalized,
-	// then advance that many runes in original.
-	// This works because our normalization only replaces runes 1:1.
-	origRunes := []rune(original)
-	normRunes := []rune(normalized)
-
-	if normIdx >= len(normRunes) {
-		return len(original)
-	}
-
-	// Count bytes for the first normIdx runes in original
-	byteCount := 0
-	for i := 0; i < normIdx && i < len(origRunes); i++ {
-		byteCount += len(string(origRunes[i]))
-	}
-	return byteCount
-}
-
-// generateDiff creates a simple unified diff showing the change.
-func generateDiff(path, old, new string, changeIdx int) string {
-	oldLines := strings.Split(old, "\n")
-	newLines := strings.Split(new, "\n")
-
-	// Find the line number where the change starts
-	lineNum := strings.Count(old[:changeIdx], "\n") + 1
-
-	// Show context around the change
-	contextLines := 3
-	start := max(lineNum-contextLines-1, 0)
-
-	var diff strings.Builder
-	fmt.Fprintf(&diff, "--- %s\n+++ %s\n", path, path)
-
-	// Find changed region
-	endOld := min(lineNum+contextLines+countNewlines(old[changeIdx:])+1, len(oldLines))
-	endNew := min(lineNum+contextLines+countNewlines(new[changeIdx:])+1, len(newLines))
-
-	fmt.Fprintf(&diff, "@@ -%d,%d +%d,%d @@\n", start+1, endOld-start, start+1, endNew-start)
-
-	// Very simplified diff: show old lines as removed, new lines as added
-	// around the change region
-	for i := start; i < endOld && i < len(oldLines); i++ {
-		prefix := " "
-		if i >= lineNum-1 && i < lineNum-1+countNewlines(old[changeIdx:])+1 {
-			prefix = "-"
+	origPos := 0
+	for li, line := range lines {
+		if li > 0 {
+			result = append(result, '\n')
+			mapping = append(mapping, origPos)
+			origPos++ // skip \n in original
 		}
-		fmt.Fprintf(&diff, "%s %s\n", prefix, oldLines[i])
+
+		trimmed := strings.TrimRightFunc(line, unicode.IsSpace)
+
+		for j := 0; j < len(trimmed); {
+			r, size := utf8.DecodeRuneInString(trimmed[j:])
+			repl := normalizeRune(r)
+			for k := 0; k < len(repl); k++ {
+				mapping = append(mapping, origPos+j)
+			}
+			result = append(result, repl...)
+			j += size
+		}
+
+		origPos += len(line) // advance past full original line including trailing ws
 	}
 
-	return diff.String()
+	return string(result), mapping
 }
 
-func countNewlines(s string) int {
-	return strings.Count(s, "\n")
+// normalizeRune maps unicode quotes, dashes, and non-breaking spaces to
+// their ASCII equivalents. Returns the original rune as a string for all
+// other characters.
+func normalizeRune(r rune) string {
+	switch r {
+	case '\u201c', '\u201d': // left/right double quote
+		return "\""
+	case '\u2018', '\u2019': // left/right single quote
+		return "'"
+	case '\u2013', '\u2014': // en dash, em dash
+		return "-"
+	case '\u00a0': // non-breaking space
+		return " "
+	default:
+		return string(r)
+	}
+}
+
+// normalizeForFuzzy normalizes s for fuzzy matching (without position mapping).
+// Used for the search string where position mapping is not needed.
+func normalizeForFuzzy(s string) string {
+	norm, _ := normalizeWithMap(s)
+	return norm
+}
+
+// generateDiff creates a unified diff showing the change between old and new
+// file contents. Uses the go-udiff library for correct diff computation.
+func generateDiff(path, old, new string) string {
+	return udiff.Unified(path, path, old, new)
 }

internal/core/edit_test.go

@@ -0,0 +1,717 @@
+package core
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"charm.land/fantasy"
+)
+
+func writeFileOrFail(t *testing.T, path, content string) {
+	t.Helper()
+	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
+		t.Fatalf("failed to write test file %s: %v", path, err)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// fuzzyMatch — the core bug fix
+// ---------------------------------------------------------------------------
+
+func TestFuzzyMatch_TrailingWhitespace(t *testing.T) {
+	// The original bug: trailing whitespace on lines caused mapFuzzyIndex
+	// to return wrong byte positions, corrupting the replacement splice.
+	content := "line1   \nline2   \nline3   \nTAIL\n"
+	search := "line2\nline3"
+
+	idx, matchLen := fuzzyMatch(content, search)
+	if idx < 0 {
+		t.Fatal("expected fuzzy match, got none")
+	}
+
+	matched := content[idx : idx+matchLen]
+	want := "line2   \nline3   "
+	if matched != want {
+		t.Errorf("matched=%q, want=%q", matched, want)
+	}
+
+	// Verify replacement is correct
+	repl := content[:idx] + "REPLACED" + content[idx+matchLen:]
+	wantRepl := "line1   \nREPLACED\nTAIL\n"
+	if repl != wantRepl {
+		t.Errorf("replacement=%q, want=%q", repl, wantRepl)
+	}
+}
+
+func TestFuzzyMatch_TrailingWhitespace_FirstLine(t *testing.T) {
+	content := "line1   \nline2   \nline3\n"
+	search := "line1\nline2"
+
+	idx, matchLen := fuzzyMatch(content, search)
+	if idx < 0 {
+		t.Fatal("expected fuzzy match")
+	}
+
+	matched := content[idx : idx+matchLen]
+	want := "line1   \nline2   "
+	if matched != want {
+		t.Errorf("matched=%q, want=%q", matched, want)
+	}
+}
+
+func TestFuzzyMatch_TrailingWhitespace_LastLine(t *testing.T) {
+	content := "HEAD\nline1   \nline2   \n"
+	search := "line1\nline2"
+
+	idx, matchLen := fuzzyMatch(content, search)
+	if idx < 0 {
+		t.Fatal("expected fuzzy match")
+	}
+
+	matched := content[idx : idx+matchLen]
+	want := "line1   \nline2   "
+	if matched != want {
+		t.Errorf("matched=%q, want=%q", matched, want)
+	}
+}
+
+func TestFuzzyMatch_TrailingWhitespace_AtEOF(t *testing.T) {
+	// Match extends to the very end of the content
+	content := "HEAD\nline1   \nline2   "
+	search := "line1\nline2"
+
+	idx, matchLen := fuzzyMatch(content, search)
+	if idx < 0 {
+		t.Fatal("expected fuzzy match")
+	}
+
+	matched := content[idx : idx+matchLen]
+	want := "line1   \nline2   "
+	if matched != want {
+		t.Errorf("matched=%q, want=%q", matched, want)
+	}
+}
+
+func TestFuzzyMatch_UnicodeQuotes(t *testing.T) {
+	content := "say \u201chello\u201d\n"
+	search := "say \"hello\"\n"
+
+	idx, matchLen := fuzzyMatch(content, search)
+	if idx < 0 {
+		t.Fatal("expected fuzzy match for unicode quotes")
+	}
+
+	matched := content[idx : idx+matchLen]
+	if matched != content { // entire content should match
+		t.Errorf("matched=%q, want=%q", matched, content)
+	}
+}
+
+func TestFuzzyMatch_SmartSingleQuotes(t *testing.T) {
+	content := "it\u2019s a test\n"
+	search := "it's a test\n"
+
+	idx, matchLen := fuzzyMatch(content, search)
+	if idx < 0 {
+		t.Fatal("expected fuzzy match for smart single quotes")
+	}
+	matched := content[idx : idx+matchLen]
+	if matched != content {
+		t.Errorf("matched=%q, want=%q", matched, content)
+	}
+}
+
+func TestFuzzyMatch_EmDash(t *testing.T) {
+	content := "foo \u2014 bar\n"
+	search := "foo - bar\n"
+
+	idx, matchLen := fuzzyMatch(content, search)
+	if idx < 0 {
+		t.Fatal("expected fuzzy match for em dash")
+	}
+	matched := content[idx : idx+matchLen]
+	if matched != content {
+		t.Errorf("matched=%q, want=%q", matched, content)
+	}
+}
+
+func TestFuzzyMatch_NonBreakingSpace(t *testing.T) {
+	content := "hello\u00a0world\n"
+	search := "hello world\n"
+
+	idx, matchLen := fuzzyMatch(content, search)
+	if idx < 0 {
+		t.Fatal("expected fuzzy match for non-breaking space")
+	}
+	matched := content[idx : idx+matchLen]
+	if matched != content {
+		t.Errorf("matched=%q, want=%q", matched, content)
+	}
+}
+
+func TestFuzzyMatch_NoMatch(t *testing.T) {
+	content := "hello world\n"
+	search := "goodbye world\n"
+
+	idx, _ := fuzzyMatch(content, search)
+	if idx >= 0 {
+		t.Error("expected no match")
+	}
+}
+
+func TestFuzzyMatch_AmbiguousReturnsNoMatch(t *testing.T) {
+	// Two identical blocks — fuzzy match should refuse to pick one
+	content := "block\nblock\n"
+	search := "block"
+
+	idx, _ := fuzzyMatch(content, search)
+	if idx >= 0 {
+		t.Error("expected no match for ambiguous fuzzy hit")
+	}
+}
+
+func TestFuzzyMatch_EmptySearch(t *testing.T) {
+	idx, _ := fuzzyMatch("content", "")
+	if idx >= 0 {
+		t.Error("expected no match for empty search")
+	}
+}
+
+func TestFuzzyMatch_MultiLineWithMixedWhitespace(t *testing.T) {
+	content := "func foo() {\t  \n\treturn 1  \n}\t \n"
+	search := "func foo() {\n\treturn 1\n}"
+
+	idx, matchLen := fuzzyMatch(content, search)
+	if idx < 0 {
+		t.Fatal("expected fuzzy match")
+	}
+
+	// Replacement should preserve surrounding content
+	repl := content[:idx] + "func bar() {\n\treturn 2\n}" + content[idx+matchLen:]
+	if !strings.HasPrefix(repl, "func bar()") {
+		t.Errorf("unexpected replacement start: %q", repl[:20])
+	}
+	if !strings.HasSuffix(repl, "\n") {
+		t.Errorf("replacement should end with newline: %q", repl)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// normalizeWithMap — position mapping correctness
+// ---------------------------------------------------------------------------
+
+func TestNormalizeWithMap_NoTrailingWhitespace(t *testing.T) {
+	s := "abc\ndef"
+	norm, mapping := normalizeWithMap(s)
+	if norm != s {
+		t.Errorf("norm=%q, want=%q", norm, s)
+	}
+	// Each byte should map to itself
+	for i, orig := range mapping {
+		if orig != i {
+			t.Errorf("mapping[%d]=%d, want=%d", i, orig, i)
+		}
+	}
+}
+
+func TestNormalizeWithMap_TrailingWhitespace(t *testing.T) {
+	s := "ab   \ncd"
+	norm, mapping := normalizeWithMap(s)
+	wantNorm := "ab\ncd"
+	if norm != wantNorm {
+		t.Errorf("norm=%q, want=%q", norm, wantNorm)
+	}
+	// 'a'→0, 'b'→1, '\n'→5, 'c'→6, 'd'→7
+	wantMapping := []int{0, 1, 5, 6, 7}
+	if len(mapping) != len(wantMapping) {
+		t.Fatalf("mapping len=%d, want=%d", len(mapping), len(wantMapping))
+	}
+	for i, want := range wantMapping {
+		if mapping[i] != want {
+			t.Errorf("mapping[%d]=%d, want=%d", i, mapping[i], want)
+		}
+	}
+}
+
+func TestNormalizeWithMap_UnicodeReplacement(t *testing.T) {
+	// \u201c is 3 bytes in UTF-8, replaced with " which is 1 byte
+	s := "\u201chello\u201d"
+	norm, mapping := normalizeWithMap(s)
+	wantNorm := "\"hello\""
+	if norm != wantNorm {
+		t.Errorf("norm=%q, want=%q", norm, wantNorm)
+	}
+	// " maps to byte 0 (start of \u201c), h maps to 3, e→4, l→5, l→6, o→7, " maps to 8 (start of \u201d)
+	wantMapping := []int{0, 3, 4, 5, 6, 7, 8}
+	if len(mapping) != len(wantMapping) {
+		t.Fatalf("mapping len=%d, want=%d", len(mapping), len(wantMapping))
+	}
+	for i, want := range wantMapping {
+		if mapping[i] != want {
+			t.Errorf("mapping[%d]=%d, want=%d", i, mapping[i], want)
+		}
+	}
+}
+
+func TestNormalizeWithMap_EmptyString(t *testing.T) {
+	norm, mapping := normalizeWithMap("")
+	if norm != "" {
+		t.Errorf("norm=%q, want empty", norm)
+	}
+	if len(mapping) != 0 {
+		t.Errorf("mapping len=%d, want 0", len(mapping))
+	}
+}
+
+func TestNormalizeWithMap_OnlyWhitespace(t *testing.T) {
+	norm, _ := normalizeWithMap("   \n   ")
+	if norm != "\n" {
+		t.Errorf("norm=%q, want %q", norm, "\n")
+	}
+}
+
+// ---------------------------------------------------------------------------
+// normalizeForFuzzy — consistency with normalizeWithMap
+// ---------------------------------------------------------------------------
+
+func TestNormalizeForFuzzy_ConsistentWithMap(t *testing.T) {
+	inputs := []string{
+		"hello   \nworld   ",
+		"\u201chello\u201d\u2014world",
+		"a\u00a0b\u2013c\n  trailing  \n",
+		"no changes here",
+		"",
+	}
+	for _, s := range inputs {
+		norm := normalizeForFuzzy(s)
+		normMap, _ := normalizeWithMap(s)
+		if norm != normMap {
+			t.Errorf("normalizeForFuzzy(%q) = %q, normalizeWithMap = %q", s, norm, normMap)
+		}
+	}
+}
+
+// ---------------------------------------------------------------------------
+// generateDiff — correct unified diff output
+// ---------------------------------------------------------------------------
+
+func TestGenerateDiff_SingleLineChange(t *testing.T) {
+	old := "line1\nline2\nline3\nline4\nline5\nline6\nline7\n"
+	new := "line1\nline2\nline3\nLINE4\nline5\nline6\nline7\n"
+
+	diff := generateDiff("test.go", old, new)
+
+	// Should contain standard unified diff markers
+	if !strings.Contains(diff, "--- test.go") {
+		t.Error("diff should contain --- header")
+	}
+	if !strings.Contains(diff, "+++ test.go") {
+		t.Error("diff should contain +++ header")
+	}
+	if !strings.Contains(diff, "@@") {
+		t.Error("diff should contain @@ hunk header")
+	}
+
+	// Should show the actual change
+	if !strings.Contains(diff, "-line4") {
+		t.Error("diff should show removed line")
+	}
+	if !strings.Contains(diff, "+LINE4") {
+		t.Error("diff should show added line")
+	}
+
+	// Should NOT mark all remaining lines as changed (the old bug)
+	deletedCount := strings.Count(diff, "\n-")
+	if deletedCount > 2 { // at most 1 deleted line + some tolerance
+		t.Errorf("diff shows %d deletions, expected ~1 (old bug: marked rest of file as deleted)", deletedCount)
+	}
+}
+
+func TestGenerateDiff_MultiLineChange(t *testing.T) {
+	old := "aaa\nbbb\nccc\nddd\n"
+	new := "aaa\nBBB\nCCC\nddd\n"
+
+	diff := generateDiff("x.go", old, new)
+	if !strings.Contains(diff, "-bbb") {
+		t.Error("diff should show bbb removed")
+	}
+	if !strings.Contains(diff, "-ccc") {
+		t.Error("diff should show ccc removed")
+	}
+	if !strings.Contains(diff, "+BBB") {
+		t.Error("diff should show BBB added")
+	}
+	if !strings.Contains(diff, "+CCC") {
+		t.Error("diff should show CCC added")
+	}
+}
+
+func TestGenerateDiff_NoChange(t *testing.T) {
+	content := "hello\nworld\n"
+	diff := generateDiff("x.go", content, content)
+	if diff != "" {
+		t.Errorf("expected empty diff for identical content, got %q", diff)
+	}
+}
+
+func TestGenerateDiff_Addition(t *testing.T) {
+	old := "line1\nline2\n"
+	new := "line1\nnew line\nline2\n"
+
+	diff := generateDiff("x.go", old, new)
+	if !strings.Contains(diff, "+new line") {
+		t.Error("diff should show added line")
+	}
+}
+
+func TestGenerateDiff_Deletion(t *testing.T) {
+	old := "line1\nremove me\nline2\n"
+	new := "line1\nline2\n"
+
+	diff := generateDiff("x.go", old, new)
+	if !strings.Contains(diff, "-remove me") {
+		t.Error("diff should show deleted line")
+	}
+}
+
+// ---------------------------------------------------------------------------
+// End-to-end: executeEdit via tool call
+// ---------------------------------------------------------------------------
+
+func TestExecuteEdit_ExactMatch(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "test.go")
+	original := "func main() {\n\tfmt.Println(\"hello\")\n}\n"
+	writeFileOrFail(t, path, original)
+
+	input, _ := json.Marshal(editArgs{
+		Path:    path,
+		OldText: "fmt.Println(\"hello\")",
+		NewText: "fmt.Println(\"world\")",
+	})
+
+	resp, err := executeEdit(t.Context(), fantasy.ToolCall{Input: string(input)}, dir)
+	if err != nil {
+		t.Fatalf("executeEdit error: %v", err)
+	}
+	if resp.IsError {
+		t.Fatalf("tool returned error: %s", resp.Content)
+	}
+
+	got, _ := os.ReadFile(path)
+	want := "func main() {\n\tfmt.Println(\"world\")\n}\n"
+	if string(got) != want {
+		t.Errorf("file content=%q, want=%q", string(got), want)
+	}
+}
+
+func TestExecuteEdit_ExactMatch_DoesNotCorruptRest(t *testing.T) {
+	// This is the key regression test for the screenshot bug: editing a
+	// small section must NOT delete/corrupt the rest of the file.
+	dir := t.TempDir()
+	path := filepath.Join(dir, "big.go")
+
+	var lines []string
+	for i := 1; i <= 100; i++ {
+		lines = append(lines, fmt.Sprintf("line_%03d_%s", i, strings.Repeat("x", 40)))
+	}
+	original := strings.Join(lines, "\n") + "\n"
+	writeFileOrFail(t, path, original)
+
+	// Replace just line 50
+	target := lines[49]
+	replacement := "REPLACED_LINE_50"
+	input, _ := json.Marshal(editArgs{
+		Path:    path,
+		OldText: target,
+		NewText: replacement,
+	})
+
+	resp, err := executeEdit(t.Context(), fantasy.ToolCall{Input: string(input)}, dir)
+	if err != nil {
+		t.Fatalf("executeEdit error: %v", err)
+	}
+	if resp.IsError {
+		t.Fatalf("tool returned error: %s", resp.Content)
+	}
+
+	got, _ := os.ReadFile(path)
+	gotLines := strings.Split(string(got), "\n")
+
+	// File should still have 101 elements (100 lines + trailing empty)
+	if len(gotLines) != 101 {
+		t.Fatalf("file has %d lines, want 101 (content was corrupted)", len(gotLines))
+	}
+
+	// Line 50 should be replaced
+	if gotLines[49] != replacement {
+		t.Errorf("line 50=%q, want=%q", gotLines[49], replacement)
+	}
+
+	// Lines before and after should be untouched
+	if gotLines[0] != lines[0] {
+		t.Errorf("line 1 corrupted: %q", gotLines[0])
+	}
+	if gotLines[98] != lines[98] {
+		t.Errorf("line 99 corrupted: %q", gotLines[98])
+	}
+}
+
+func TestExecuteEdit_FuzzyMatch_TrailingWhitespace(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "ws.go")
+	// File has trailing whitespace on some lines
+	original := "func foo() {   \n\treturn 1   \n}\nfunc bar() {\n}\n"
+	writeFileOrFail(t, path, original)
+
+	// Search without trailing whitespace (common LLM behavior)
+	input, _ := json.Marshal(editArgs{
+		Path:    path,
+		OldText: "func foo() {\n\treturn 1\n}",
+		NewText: "func foo() {\n\treturn 2\n}",
+	})
+
+	resp, err := executeEdit(t.Context(), fantasy.ToolCall{Input: string(input)}, dir)
+	if err != nil {
+		t.Fatalf("executeEdit error: %v", err)
+	}
+	if resp.IsError {
+		t.Fatalf("tool returned error: %s", resp.Content)
+	}
+
+	got, _ := os.ReadFile(path)
+	gotStr := string(got)
+
+	// The fuzzy match replaces the matched region (which includes trailing
+	// whitespace) with the new_text. The key invariant is that the rest of
+	// the file (func bar) must be preserved.
+	if !strings.Contains(gotStr, "return 2") {
+		t.Error("edit was not applied: missing 'return 2'")
+	}
+	if !strings.Contains(gotStr, "func bar()") {
+		t.Errorf("file was corrupted: missing func bar(). got=%q", gotStr)
+	}
+
+	// Verify response mentions fuzzy match
+	if !strings.Contains(resp.Content, "fuzzy match") {
+		t.Error("response should mention fuzzy match")
+	}
+}
+
+func TestExecuteEdit_FuzzyMatch_DoesNotCorruptRest(t *testing.T) {
+	// Regression test: fuzzy match must not corrupt content after the match.
+	dir := t.TempDir()
+	path := filepath.Join(dir, "fuzzy.txt")
+
+	// 20 lines, each with trailing whitespace
+	var lines []string
+	for i := 1; i <= 20; i++ {
+		lines = append(lines, strings.Repeat("x", 10)+"   ") // trailing spaces
+	}
+	original := strings.Join(lines, "\n") + "\nEND\n"
+	writeFileOrFail(t, path, original)
+
+	// Search for lines 10-11 without trailing whitespace
+	search := strings.Repeat("x", 10) + "\n" + strings.Repeat("x", 10)
+	// But this matches lines 1-2, 2-3, etc. — should fail due to ambiguity.
+	input, _ := json.Marshal(editArgs{
+		Path:    path,
+		OldText: search,
+		NewText: "REPLACED",
+	})
+
+	resp, err := executeEdit(t.Context(), fantasy.ToolCall{Input: string(input)}, dir)
+	if err != nil {
+		t.Fatalf("executeEdit error: %v", err)
+	}
+
+	// This should either fail (ambiguous) or produce correct output.
+	// With identical lines, fuzzy match should refuse (ambiguous).
+	got, _ := os.ReadFile(path)
+	if !resp.IsError {
+		// If it didn't error, verify the file is not corrupted
+		if !strings.HasSuffix(string(got), "END\n") {
+			t.Error("file was corrupted: missing END marker")
+		}
+	}
+}
+
+func TestExecuteEdit_MultipleMatches_Fails(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "dup.txt")
+	writeFileOrFail(t, path, "hello\nworld\nhello\n")
+
+	input, _ := json.Marshal(editArgs{
+		Path:    path,
+		OldText: "hello",
+		NewText: "goodbye",
+	})
+
+	resp, err := executeEdit(t.Context(), fantasy.ToolCall{Input: string(input)}, dir)
+	if err != nil {
+		t.Fatalf("executeEdit error: %v", err)
+	}
+	if !resp.IsError {
+		t.Error("expected error for multiple matches")
+	}
+	if !strings.Contains(resp.Content, "2 matches") {
+		t.Errorf("expected '2 matches' in error, got: %s", resp.Content)
+	}
+
+	// File should be untouched
+	got, _ := os.ReadFile(path)
+	if string(got) != "hello\nworld\nhello\n" {
+		t.Error("file was modified despite error")
+	}
+}
+
+func TestExecuteEdit_NoMatch_Fails(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "nomatch.txt")
+	writeFileOrFail(t, path, "hello world\n")
+
+	input, _ := json.Marshal(editArgs{
+		Path:    path,
+		OldText: "nonexistent text",
+		NewText: "replacement",
+	})
+
+	resp, err := executeEdit(t.Context(), fantasy.ToolCall{Input: string(input)}, dir)
+	if err != nil {
+		t.Fatalf("executeEdit error: %v", err)
+	}
+	if !resp.IsError {
+		t.Error("expected error for no match")
+	}
+
+	// File should be untouched
+	got, _ := os.ReadFile(path)
+	if string(got) != "hello world\n" {
+		t.Error("file was modified despite error")
+	}
+}
+
+func TestExecuteEdit_CRLFNormalization(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "crlf.txt")
+	writeFileOrFail(t, path, "line1\r\nline2\r\nline3\r\n")
+
+	input, _ := json.Marshal(editArgs{
+		Path:    path,
+		OldText: "line2",
+		NewText: "LINE2",
+	})
+
+	resp, err := executeEdit(t.Context(), fantasy.ToolCall{Input: string(input)}, dir)
+	if err != nil {
+		t.Fatalf("executeEdit error: %v", err)
+	}
+	if resp.IsError {
+		t.Fatalf("tool returned error: %s", resp.Content)
+	}
+
+	got, _ := os.ReadFile(path)
+	if !strings.Contains(string(got), "LINE2") {
+		t.Error("edit was not applied")
+	}
+}
+
+func TestExecuteEdit_MissingPath(t *testing.T) {
+	input, _ := json.Marshal(editArgs{
+		OldText: "x",
+		NewText: "y",
+	})
+	resp, err := executeEdit(t.Context(), fantasy.ToolCall{Input: string(input)}, "")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !resp.IsError {
+		t.Error("expected error for missing path")
+	}
+}
+
+func TestExecuteEdit_NonexistentFile(t *testing.T) {
+	input, _ := json.Marshal(editArgs{
+		Path:    "/tmp/nonexistent_edit_test_file_12345.go",
+		OldText: "x",
+		NewText: "y",
+	})
+	resp, err := executeEdit(t.Context(), fantasy.ToolCall{Input: string(input)}, "")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !resp.IsError {
+		t.Error("expected error for nonexistent file")
+	}
+}
+
+func TestExecuteEdit_DiffContainsHunkHeader(t *testing.T) {
+	// The UI's extractDiffStartLine parses @@ -N from the result.
+	// Verify the diff output contains it.
+	dir := t.TempDir()
+	path := filepath.Join(dir, "hunk.go")
+	var lines []string
+	for i := 1; i <= 20; i++ {
+		lines = append(lines, fmt.Sprintf("line_%02d_content", i))
+	}
+	writeFileOrFail(t, path, strings.Join(lines, "\n")+"\n")
+
+	input, _ := json.Marshal(editArgs{
+		Path:    path,
+		OldText: "line_10_content",
+		NewText: "REPLACED",
+	})
+
+	resp, err := executeEdit(t.Context(), fantasy.ToolCall{Input: string(input)}, dir)
+	if err != nil {
+		t.Fatalf("error: %v", err)
+	}
+	if resp.IsError {
+		t.Fatalf("tool error: %s", resp.Content)
+	}
+	if !strings.Contains(resp.Content, "@@ ") {
+		t.Error("diff output should contain @@ hunk header for UI parsing")
+	}
+}
+
+func TestExecuteEdit_MetadataContainsFileDiffs(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "meta.go")
+	writeFileOrFail(t, path, "old content\n")
+
+	input, _ := json.Marshal(editArgs{
+		Path:    path,
+		OldText: "old content",
+		NewText: "new content",
+	})
+
+	resp, err := executeEdit(t.Context(), fantasy.ToolCall{Input: string(input)}, dir)
+	if err != nil {
+		t.Fatalf("error: %v", err)
+	}
+
+	// Check metadata is present
+	metaJSON := resp.Metadata
+	if metaJSON == "" {
+		t.Fatal("expected metadata on response")
+	}
+
+	var meta map[string]any
+	if err := json.Unmarshal([]byte(metaJSON), &meta); err != nil {
+		t.Fatalf("metadata is not valid JSON: %v", err)
+	}
+
+	diffs, ok := meta["file_diffs"]
+	if !ok {
+		t.Fatal("metadata missing file_diffs key")
+	}
+
+	diffList, ok := diffs.([]any)
+	if !ok || len(diffList) == 0 {
+		t.Fatal("file_diffs should be a non-empty array")
+	}
+}

internal/core/find.go

@@ -39,6 +39,7 @@ func NewFindTool(opts ...ToolOption) fantasy.AgentTool {
 				},
 			},
 			Required: []string{"pattern"},
+			Parallel: true,
 		},
 		handler: func(ctx context.Context, call fantasy.ToolCall) (fantasy.ToolResponse, error) {
 			return executeFind(ctx, call, cfg.WorkDir)

internal/core/grep.go

@@ -59,6 +59,7 @@ func NewGrepTool(opts ...ToolOption) fantasy.AgentTool {
 				},
 			},
 			Required: []string{"pattern"},
+			Parallel: true,
 		},
 		handler: func(ctx context.Context, call fantasy.ToolCall) (fantasy.ToolResponse, error) {
 			return executeGrep(ctx, call, cfg.WorkDir)

internal/core/ls.go

@@ -33,6 +33,7 @@ func NewLsTool(opts ...ToolOption) fantasy.AgentTool {
 				},
 			},
 			Required: []string{},
+			Parallel: true,
 		},
 		handler: func(ctx context.Context, call fantasy.ToolCall) (fantasy.ToolResponse, error) {
 			return executeLs(ctx, call, cfg.WorkDir)

internal/core/read.go

@@ -38,6 +38,7 @@ func NewReadTool(opts ...ToolOption) fantasy.AgentTool {
 				},
 			},
 			Required: []string{"path"},
+			Parallel: true,
 		},
 		handler: func(ctx context.Context, call fantasy.ToolCall) (fantasy.ToolResponse, error) {
 			return executeRead(ctx, call, cfg.WorkDir)

internal/core/subagent.go

@@ -0,0 +1,214 @@
+package core
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"charm.land/fantasy"
+)
+
+const defaultSubagentTimeout = 5 * time.Minute
+const maxSubagentTimeout = 30 * time.Minute
+
+// ---------------------------------------------------------------------------
+// Context-based subagent spawner
+// ---------------------------------------------------------------------------
+
+// SubagentSpawnResult carries the outcome of an in-process subagent spawn.
+type SubagentSpawnResult struct {
+	Response     string
+	Error        error
+	SessionID    string
+	InputTokens  int64
+	OutputTokens int64
+	Elapsed      time.Duration
+}
+
+// SubagentSpawnFunc is a callback that spawns an in-process subagent. The
+// parent Kit instance injects this into the context so the core tool can
+// call back without importing pkg/kit (which would create a cycle).
+// The toolCallID parameter is the LLM-assigned ID of the spawn_subagent
+// tool call, enabling the parent to correlate subagent events.
+type SubagentSpawnFunc func(ctx context.Context, toolCallID, prompt, model, systemPrompt string, timeout time.Duration) (*SubagentSpawnResult, error)
+
+type subagentCtxKey struct{}
+
+// WithSubagentSpawner stores a spawn function in the context so that the
+// spawn_subagent core tool can create in-process subagents.
+func WithSubagentSpawner(ctx context.Context, fn SubagentSpawnFunc) context.Context {
+	return context.WithValue(ctx, subagentCtxKey{}, fn)
+}
+
+// getSubagentSpawner retrieves the spawn function from the context.
+func getSubagentSpawner(ctx context.Context) SubagentSpawnFunc {
+	if fn, ok := ctx.Value(subagentCtxKey{}).(SubagentSpawnFunc); ok {
+		return fn
+	}
+	return nil
+}
+
+// ---------------------------------------------------------------------------
+// spawn_subagent tool
+// ---------------------------------------------------------------------------
+
+type subagentArgs struct {
+	Task           string `json:"task"`
+	Model          string `json:"model,omitempty"`
+	SystemPrompt   string `json:"system_prompt,omitempty"`
+	TimeoutSeconds int    `json:"timeout_seconds,omitempty"`
+}
+
+// NewSubagentTool creates the spawn_subagent core tool.
+func NewSubagentTool(opts ...ToolOption) fantasy.AgentTool {
+	return &coreTool{
+		info: fantasy.ToolInfo{
+			Name: "spawn_subagent",
+			Description: `Spawn a subagent to perform a task autonomously.
+
+The subagent runs as a separate in-process Kit instance with full tool access
+(except spawning further subagents). Use this to:
+- Delegate independent subtasks that can run in parallel
+- Perform research or analysis without blocking your main work
+- Execute tasks that benefit from a fresh context window
+
+The subagent result is returned when it completes. For long-running tasks,
+consider breaking them into smaller focused subtasks.
+
+Example use cases:
+- "Research the authentication patterns in this codebase"
+- "Write unit tests for the UserService class"
+- "Analyze the performance bottlenecks in the database queries"`,
+			Parameters: map[string]any{
+				"task": map[string]any{
+					"type":        "string",
+					"description": "The complete task description for the subagent to perform",
+				},
+				"model": map[string]any{
+					"type":        "string",
+					"description": "Optional model override (e.g. 'anthropic/claude-haiku-3-5-20241022' for faster/cheaper tasks)",
+				},
+				"system_prompt": map[string]any{
+					"type":        "string",
+					"description": "Optional system prompt for domain-specific guidance",
+				},
+				"timeout_seconds": map[string]any{
+					"type":        "number",
+					"description": "Maximum execution time in seconds (default: 300, max: 1800)",
+				},
+			},
+			Required: []string{"task"},
+			Parallel: true,
+		},
+		handler: func(ctx context.Context, call fantasy.ToolCall) (fantasy.ToolResponse, error) {
+			return executeSubagent(ctx, call)
+		},
+	}
+}
+
+func executeSubagent(ctx context.Context, call fantasy.ToolCall) (fantasy.ToolResponse, error) {
+	var args subagentArgs
+	if err := parseArgs(call.Input, &args); err != nil {
+		return fantasy.NewTextErrorResponse("task parameter is required"), nil
+	}
+	if args.Task == "" {
+		return fantasy.NewTextErrorResponse("task parameter is required"), nil
+	}
+
+	// Determine timeout.
+	timeout := defaultSubagentTimeout
+	if args.TimeoutSeconds > 0 {
+		timeout = min(time.Duration(args.TimeoutSeconds)*time.Second, maxSubagentTimeout)
+	}
+
+	// Retrieve in-process spawner from context.
+	spawner := getSubagentSpawner(ctx)
+	if spawner == nil {
+		return fantasy.NewTextErrorResponse(
+			"Error: subagent spawner not available. " +
+				"Ensure Kit is initialized with subagent support.",
+		), fmt.Errorf("no subagent spawner in context")
+	}
+
+	// Detach from the parent's deadline so the subagent gets its own
+	// independent timeout (applied downstream in Kit.Subagent). The parent
+	// context may carry a tight deadline from the LLM generation loop or
+	// other tool timeouts that would prematurely kill the subagent.
+	// We preserve context values (spawner, etc.) and propagate parent
+	// cancellation (e.g. user hits Ctrl-C) without inheriting the deadline.
+	spawnCtx := detachedWithCancel(ctx)
+
+	// Spawn in-process subagent.
+	result, err := spawner(spawnCtx, call.ID, args.Task, args.Model, args.SystemPrompt, timeout)
+	if err != nil || result.Error != nil {
+		spawnErr := err
+		if spawnErr == nil {
+			spawnErr = result.Error
+		}
+		response := fmt.Sprintf("Subagent failed after %ds.\n\nError: %v",
+			int(result.Elapsed.Seconds()), spawnErr)
+		if result.Response != "" {
+			response += fmt.Sprintf("\n\nPartial output:\n%s", truncateResponse(result.Response, 8000))
+		}
+		return fantasy.NewTextErrorResponse(response), nil
+	}
+
+	// Build successful response.
+	response := fmt.Sprintf("Subagent completed successfully in %ds.", int(result.Elapsed.Seconds()))
+	if result.InputTokens > 0 || result.OutputTokens > 0 {
+		response += fmt.Sprintf(" (tokens: %d in / %d out)", result.InputTokens, result.OutputTokens)
+	}
+	response += fmt.Sprintf("\n\nResult:\n%s", truncateResponse(result.Response, 12000))
+
+	resp := fantasy.NewTextResponse(response)
+
+	// Attach subagent session ID as metadata when available.
+	if result.SessionID != "" {
+		resp = fantasy.WithResponseMetadata(resp, map[string]any{
+			"subagent_session_id": result.SessionID,
+		})
+	}
+
+	return resp, nil
+}
+
+// ---------------------------------------------------------------------------
+// Context detachment
+// ---------------------------------------------------------------------------
+
+// detachedContext wraps a parent context, preserving its values but removing
+// its deadline and cancellation. This allows the subagent to have its own
+// independent timeout while still accessing context-stored values (e.g. the
+// subagent spawner function).
+type detachedContext struct {
+	parent context.Context
+}
+
+func (d detachedContext) Deadline() (time.Time, bool) { return time.Time{}, false }
+func (d detachedContext) Done() <-chan struct{}       { return nil }
+func (d detachedContext) Err() error                  { return nil }
+func (d detachedContext) Value(key any) any           { return d.parent.Value(key) }
+
+// detachedWithCancel creates a new context that inherits values from the
+// parent but has no deadline. Cancellation of the parent is propagated: when
+// the parent is cancelled the returned context is also cancelled, but the
+// parent's deadline does not apply to the child.
+func detachedWithCancel(parent context.Context) context.Context {
+	child, cancel := context.WithCancel(detachedContext{parent: parent})
+	go func() {
+		select {
+		case <-parent.Done():
+			cancel()
+		case <-child.Done():
+		}
+	}()
+	return child
+}
+
+// truncateResponse limits the response length to avoid overwhelming context windows.
+func truncateResponse(s string, maxLen int) string {
+	if len(s) <= maxLen {
+		return s
+	}
+	return s[:maxLen] + "\n\n... [truncated — " + fmt.Sprintf("%d", len(s)-maxLen) + " bytes omitted]"
+}

internal/core/tools.go

@@ -1,7 +1,7 @@
 // Package core provides the built-in core tools for KIT's coding agent.
 // These tools are direct fantasy.AgentTool implementations — no MCP layer,
-// no JSON-RPC, no serialization overhead. They match the pi coding agent's
-// core tool set: bash, read, write, edit, grep, find, ls.
+// no JSON-RPC, no serialization overhead. Core tool set: bash, read, write,
+// edit, grep, find, ls.
 package core
 
 import (
@@ -65,7 +65,7 @@ func parseArgs(input string, target any) error {
 }
 
 // CodingTools returns the default set of core tools for a coding agent:
-// bash, read, write, edit. This matches pi's codingTools collection.
+// bash, read, write, edit.
 func CodingTools(opts ...ToolOption) []fantasy.AgentTool {
 	return []fantasy.AgentTool{
 		NewBashTool(opts...),
@@ -76,7 +76,7 @@ func CodingTools(opts ...ToolOption) []fantasy.AgentTool {
 }
 
 // ReadOnlyTools returns tools for read-only exploration:
-// read, grep, find, ls. This matches pi's readOnlyTools collection.
+// read, grep, find, ls.
 func ReadOnlyTools(opts ...ToolOption) []fantasy.AgentTool {
 	return []fantasy.AgentTool{
 		NewReadTool(opts...),
@@ -86,8 +86,9 @@ func ReadOnlyTools(opts ...ToolOption) []fantasy.AgentTool {
 	}
 }
 
-// AllTools returns all available core tools.
-func AllTools(opts ...ToolOption) []fantasy.AgentTool {
+// SubagentTools returns all core tools except spawn_subagent. This prevents
+// infinite recursion when a subagent is itself a Kit instance.
+func SubagentTools(opts ...ToolOption) []fantasy.AgentTool {
 	return []fantasy.AgentTool{
 		NewBashTool(opts...),
 		NewReadTool(opts...),
@@ -98,3 +99,8 @@ func AllTools(opts ...ToolOption) []fantasy.AgentTool {
 		NewLsTool(opts...),
 	}
 }
+
+// AllTools returns all available core tools.
+func AllTools(opts ...ToolOption) []fantasy.AgentTool {
+	return append(SubagentTools(opts...), NewSubagentTool(opts...))
+}

internal/core/truncate.go

@@ -6,9 +6,17 @@ import (
 )
 
 const (
-	defaultMaxLines = 2000
-	defaultMaxBytes = 50 * 1024 // 50KB
-	grepMaxLineLen  = 500
+	defaultMaxLines   = 2000
+	defaultMaxBytes   = 50 * 1024 // 50KB
+	defaultMaxLineLen = 2000      // max characters per line before truncation
+	grepMaxLineLen    = 500
+
+	// DefaultMaxLines is the exported default line limit for truncation.
+	DefaultMaxLines = defaultMaxLines
+	// DefaultMaxBytes is the exported default byte limit for truncation.
+	DefaultMaxBytes = defaultMaxBytes
+	// DefaultMaxLineLen is the exported default per-line character limit.
+	DefaultMaxLineLen = defaultMaxLineLen
 )
 
 // TruncationResult describes how output was truncated.
@@ -20,9 +28,11 @@ type TruncationResult struct {
 	Kept      int    // lines kept after truncation
 }
 
-// truncateTail keeps the last maxLines lines and at most maxBytes bytes.
+// TruncateTail keeps the last maxLines lines and at most maxBytes bytes.
+// Individual lines longer than defaultMaxLineLen are truncated to prevent
+// extremely long single lines from blowing up the TUI when wrapped.
 // Used for bash output where the tail is most relevant.
-func truncateTail(content string, maxLines, maxBytes int) TruncationResult {
+func TruncateTail(content string, maxLines, maxBytes int) TruncationResult {
 	if maxLines <= 0 {
 		maxLines = defaultMaxLines
 	}
@@ -33,11 +43,11 @@ func truncateTail(content string, maxLines, maxBytes int) TruncationResult {
 	lines := strings.Split(content, "\n")
 	total := len(lines)
 
-	if len(content) <= maxBytes && total <= maxLines {
-		return TruncationResult{Content: content, Total: total, Kept: total}
-	}
+	// Truncate individual long lines first to prevent single lines from
+	// wrapping into hundreds of visual lines in the TUI.
+	lines = truncateLongLines(lines, defaultMaxLineLen)
 
-	// Truncate by lines first (keep tail)
+	// Truncate by lines (keep tail)
 	truncBy := ""
 	if total > maxLines {
 		lines = lines[total-maxLines:]
@@ -73,6 +83,7 @@ func truncateTail(content string, maxLines, maxBytes int) TruncationResult {
 }
 
 // truncateHead keeps the first maxLines lines and at most maxBytes bytes.
+// Individual lines longer than defaultMaxLineLen are truncated.
 // Used for read, grep, find, ls output where the head is most relevant.
 func truncateHead(content string, maxLines, maxBytes int) TruncationResult {
 	if maxLines <= 0 {
@@ -85,9 +96,8 @@ func truncateHead(content string, maxLines, maxBytes int) TruncationResult {
 	lines := strings.Split(content, "\n")
 	total := len(lines)
 
-	if len(content) <= maxBytes && total <= maxLines {
-		return TruncationResult{Content: content, Total: total, Kept: total}
-	}
+	// Truncate individual long lines first.
+	lines = truncateLongLines(lines, defaultMaxLineLen)
 
 	truncBy := ""
 	if total > maxLines {
@@ -120,6 +130,19 @@ func truncateHead(content string, maxLines, maxBytes int) TruncationResult {
 	}
 }
 
+// truncateLongLines caps each line to maxLen characters, appending a
+// "[...N chars truncated]" marker to any line that exceeds the limit.
+// This prevents a single very long line (e.g. minified JSON/JS) from
+// wrapping into hundreds of visual rows and blowing up the TUI.
+func truncateLongLines(lines []string, maxLen int) []string {
+	for i, line := range lines {
+		if len(line) > maxLen {
+			lines[i] = line[:maxLen] + fmt.Sprintf("... [%d chars truncated]", len(line)-maxLen)
+		}
+	}
+	return lines
+}
+
 // truncateLine truncates a single line to maxChars, appending "..." if cut.
 func truncateLine(line string, maxChars int) string {
 	if maxChars <= 0 {

internal/core/truncate_test.go

@@ -0,0 +1,163 @@
+package core
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestTruncateTail_LongLines(t *testing.T) {
+	// A single line of 5000 chars should be truncated to defaultMaxLineLen.
+	longLine := strings.Repeat("x", 5000)
+	tr := TruncateTail(longLine, 2000, 50*1024)
+
+	if len(tr.Content) > defaultMaxLineLen+100 { // +100 for the "[...N chars truncated]" suffix
+		t.Errorf("single long line not truncated: got %d chars, want <= %d", len(tr.Content), defaultMaxLineLen+100)
+	}
+	if !strings.Contains(tr.Content, "chars truncated]") {
+		t.Error("truncated line should contain truncation marker")
+	}
+}
+
+func TestTruncateTail_NormalLines(t *testing.T) {
+	// Lines within the limit should pass through unchanged.
+	content := "line1\nline2\nline3"
+	tr := TruncateTail(content, 2000, 50*1024)
+	if tr.Content != content {
+		t.Errorf("got %q, want %q", tr.Content, content)
+	}
+	if tr.Truncated {
+		t.Error("should not be marked as truncated")
+	}
+}
+
+func TestTruncateTail_LineCount(t *testing.T) {
+	lines := make([]string, 100)
+	for i := range lines {
+		lines[i] = "line"
+	}
+	content := strings.Join(lines, "\n")
+	tr := TruncateTail(content, 10, 50*1024)
+
+	if !tr.Truncated {
+		t.Error("should be marked as truncated")
+	}
+	if tr.Total != 100 {
+		t.Errorf("total = %d, want 100", tr.Total)
+	}
+	if tr.Kept != 10 {
+		t.Errorf("kept = %d, want 10", tr.Kept)
+	}
+}
+
+func TestTruncateHead_LongLines(t *testing.T) {
+	longLine := strings.Repeat("y", 5000)
+	tr := truncateHead(longLine, 2000, 50*1024)
+
+	if len(tr.Content) > defaultMaxLineLen+100 {
+		t.Errorf("single long line not truncated: got %d chars, want <= %d", len(tr.Content), defaultMaxLineLen+100)
+	}
+	if !strings.Contains(tr.Content, "chars truncated]") {
+		t.Error("truncated line should contain truncation marker")
+	}
+}
+
+func TestTruncateHead_NormalLines(t *testing.T) {
+	content := "line1\nline2\nline3"
+	tr := truncateHead(content, 2000, 50*1024)
+	if tr.Content != content {
+		t.Errorf("got %q, want %q", tr.Content, content)
+	}
+	if tr.Truncated {
+		t.Error("should not be marked as truncated")
+	}
+}
+
+func TestTruncateHead_LineCount(t *testing.T) {
+	lines := make([]string, 100)
+	for i := range lines {
+		lines[i] = "line"
+	}
+	content := strings.Join(lines, "\n")
+	tr := truncateHead(content, 10, 50*1024)
+
+	if !tr.Truncated {
+		t.Error("should be marked as truncated")
+	}
+	if tr.Total != 100 {
+		t.Errorf("total = %d, want 100", tr.Total)
+	}
+	if tr.Kept != 10 {
+		t.Errorf("kept = %d, want 10", tr.Kept)
+	}
+}
+
+func TestTruncateLongLines(t *testing.T) {
+	lines := []string{
+		"short",
+		strings.Repeat("a", 3000),
+		"also short",
+	}
+	result := truncateLongLines(lines, 100)
+
+	if result[0] != "short" {
+		t.Error("short line should be unchanged")
+	}
+	if len(result[1]) > 200 { // 100 chars + marker
+		t.Errorf("long line not truncated: len=%d", len(result[1]))
+	}
+	if !strings.Contains(result[1], "chars truncated]") {
+		t.Error("should contain truncation marker")
+	}
+	if result[2] != "also short" {
+		t.Error("short line should be unchanged")
+	}
+}
+
+func TestTruncateTail_MixedLongAndManyLines(t *testing.T) {
+	// 50 lines, each 3000 chars — tests both per-line and total truncation.
+	lines := make([]string, 50)
+	for i := range lines {
+		lines[i] = strings.Repeat("z", 3000)
+	}
+	content := strings.Join(lines, "\n")
+
+	tr := TruncateTail(content, 10, 50*1024)
+
+	// Should keep 10 lines.
+	if tr.Kept != 10 {
+		t.Errorf("kept = %d, want 10", tr.Kept)
+	}
+	// Each line should be capped at ~defaultMaxLineLen.
+	resultLines := strings.Split(tr.Content, "\n")
+	for i, line := range resultLines {
+		if len(line) > defaultMaxLineLen+100 {
+			t.Errorf("line %d too long: %d chars", i, len(line))
+		}
+	}
+}
+
+func TestTruncateLine(t *testing.T) {
+	short := "hello"
+	if truncateLine(short, 10) != short {
+		t.Error("short line should be unchanged")
+	}
+
+	long := strings.Repeat("x", 100)
+	result := truncateLine(long, 10)
+	if len(result) != 13 { // 10 + "..."
+		t.Errorf("got len %d, want 13", len(result))
+	}
+
+	// Default max for 0 — input shorter than default, so unchanged
+	result2 := truncateLine(long, 0)
+	if result2 != long {
+		t.Errorf("100-char line should be unchanged when maxChars defaults to %d", grepMaxLineLen)
+	}
+
+	// Longer input with default
+	veryLong := strings.Repeat("x", 1000)
+	result3 := truncateLine(veryLong, 0)
+	if len(result3) != grepMaxLineLen+3 {
+		t.Errorf("got len %d, want %d", len(result3), grepMaxLineLen+3)
+	}
+}

internal/core/write.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"charm.land/fantasy"
 )
@@ -53,6 +54,14 @@ func executeWrite(ctx context.Context, call fantasy.ToolCall, workDir string) (f
 		return fantasy.NewTextErrorResponse(fmt.Sprintf("invalid path: %v", err)), nil
 	}
 
+	// Read existing content before writing (for diff metadata).
+	var beforeContent string
+	isNew := true
+	if existing, readErr := os.ReadFile(absPath); readErr == nil {
+		beforeContent = string(existing)
+		isNew = false
+	}
+
 	// Create parent directories
 	dir := filepath.Dir(absPath)
 	if err := os.MkdirAll(dir, 0755); err != nil {
@@ -63,5 +72,27 @@ func executeWrite(ctx context.Context, call fantasy.ToolCall, workDir string) (f
 		return fantasy.NewTextErrorResponse(fmt.Sprintf("failed to write file: %v", err)), nil
 	}
 
-	return fantasy.NewTextResponse(fmt.Sprintf("Wrote %d bytes to %s", len(args.Content), args.Path)), nil
+	resp := fantasy.NewTextResponse(fmt.Sprintf("Wrote %d bytes to %s", len(args.Content), args.Path))
+	return fantasy.WithResponseMetadata(resp, writeDiffMeta(absPath, beforeContent, args.Content, isNew)), nil
+}
+
+// writeDiffMeta builds the structured metadata attached to write tool responses.
+func writeDiffMeta(path, beforeContent, afterContent string, isNew bool) map[string]any {
+	additions := strings.Count(afterContent, "\n") + 1
+	deletions := 0
+	if !isNew {
+		deletions = strings.Count(beforeContent, "\n") + 1
+	}
+	return map[string]any{
+		"file_diffs": []map[string]any{{
+			"path":      path,
+			"additions": additions,
+			"deletions": deletions,
+			"is_new":    isNew,
+			"diff_blocks": []map[string]any{{
+				"old_text": beforeContent,
+				"new_text": afterContent,
+			}},
+		}},
+	}
 }

internal/extensions/events.go

@@ -1,4 +1,4 @@
-// Package extensions implements a Pi-style in-process extension system for KIT.
+// Package extensions implements an in-process extension system for KIT.
 // Extensions are plain Go files loaded at runtime via Yaegi (a Go interpreter).
 // They register event handlers using an API object, enabling tool interception,
 // input transformation, and lifecycle observation — all without recompilation.
@@ -19,6 +19,9 @@ const (
 	// ToolExecutionEnd fires when a tool finishes executing.
 	ToolExecutionEnd EventType = "tool_execution_end"
 
+	// ToolOutput fires when a tool produces streaming output chunks.
+	ToolOutput EventType = "tool_output"
+
 	// ToolResult fires after a tool executes. Handlers can modify the result.
 	ToolResult EventType = "tool_result"
 
@@ -48,6 +51,38 @@ const (
 
 	// SessionShutdown fires when the application is closing.
 	SessionShutdown EventType = "session_shutdown"
+
+	// ModelChange fires after the active model is changed via ctx.SetModel().
+	ModelChange EventType = "model_change"
+
+	// ContextPrepare fires after context is built from the session tree and
+	// before the messages are sent to the LLM. Handlers can filter, reorder,
+	// or inject messages into the context window.
+	ContextPrepare EventType = "context_prepare"
+
+	// BeforeFork fires before the session tree is branched to a different
+	// entry point. Handlers can cancel the fork by returning Cancel=true.
+	BeforeFork EventType = "before_fork"
+
+	// BeforeSessionSwitch fires before the session is switched to a new
+	// branch (e.g. /new command). Handlers can cancel by returning Cancel=true.
+	BeforeSessionSwitch EventType = "before_session_switch"
+
+	// BeforeCompact fires before context compaction runs. Handlers can
+	// cancel compaction by returning Cancel=true.
+	BeforeCompact EventType = "before_compact"
+
+	// SubagentStart fires when a spawn_subagent tool call begins executing.
+	// Carries the tool call ID and the task description.
+	SubagentStart EventType = "subagent_start"
+
+	// SubagentChunk fires for each real-time event emitted by a running
+	// subagent: text chunks, tool calls, tool results, etc.
+	SubagentChunk EventType = "subagent_chunk"
+
+	// SubagentEnd fires when a spawn_subagent tool call completes (success
+	// or error). Carries the final response and any error message.
+	SubagentEnd EventType = "subagent_end"
 )
 
 // AllEventTypes returns every supported event type.
@@ -57,6 +92,9 @@ func AllEventTypes() []EventType {
 		Input, BeforeAgentStart, AgentStart, AgentEnd,
 		MessageStart, MessageUpdate, MessageEnd,
 		SessionStart, SessionShutdown,
+		ModelChange, ContextPrepare,
+		BeforeFork, BeforeSessionSwitch, BeforeCompact,
+		SubagentStart, SubagentChunk, SubagentEnd,
 	}
 }
 

internal/extensions/events_test.go

@@ -4,8 +4,8 @@ import "testing"
 
 func TestAllEventTypes_Count(t *testing.T) {
 	all := AllEventTypes()
-	if len(all) != 13 {
-		t.Fatalf("expected 13 event types, got %d", len(all))
+	if len(all) != 21 {
+		t.Fatalf("expected 21 event types, got %d", len(all))
 	}
 }
 
@@ -50,6 +50,14 @@ func TestEventType_TypeMethod(t *testing.T) {
 		{MessageEndEvent{Content: "done"}, MessageEnd},
 		{SessionStartEvent{SessionID: "abc"}, SessionStart},
 		{SessionShutdownEvent{}, SessionShutdown},
+		{ModelChangeEvent{NewModel: "a/b"}, ModelChange},
+		{ContextPrepareEvent{Messages: []ContextMessage{{Index: 0, Role: "user", Content: "hi"}}}, ContextPrepare},
+		{BeforeForkEvent{TargetID: "abc"}, BeforeFork},
+		{BeforeSessionSwitchEvent{Reason: "new"}, BeforeSessionSwitch},
+		{BeforeCompactEvent{EstimatedTokens: 1000}, BeforeCompact},
+		{SubagentStartEvent{ToolCallID: "x", Task: "t"}, SubagentStart},
+		{SubagentChunkEvent{ToolCallID: "x", ChunkType: "text"}, SubagentChunk},
+		{SubagentEndEvent{ToolCallID: "x"}, SubagentEnd},
 	}
 
 	for _, tt := range tests {

internal/extensions/installer.go

@@ -0,0 +1,537 @@
+package extensions
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/url"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+// InstallScope defines where a package should be installed.
+type InstallScope string
+
+const (
+	ScopeGlobal  InstallScope = "global"
+	ScopeProject InstallScope = "project"
+)
+
+// GitSource represents a parsed git repository URL.
+type GitSource struct {
+	Repo   string // Clone URL (e.g., https://github.com/user/repo.git)
+	Host   string // Host (e.g., github.com)
+	Path   string // Path (e.g., user/repo)
+	Ref    string // Optional ref (tag, branch, commit)
+	Pinned bool   // Whether a specific ref is pinned
+}
+
+// String returns the canonical string representation.
+func (g GitSource) String() string {
+	if g.Pinned {
+		return fmt.Sprintf("git:%s/%s@%s", g.Host, g.Path, g.Ref)
+	}
+	return fmt.Sprintf("git:%s/%s", g.Host, g.Path)
+}
+
+// Identity returns a normalized identity string for deduplication.
+func (g GitSource) Identity() string {
+	return fmt.Sprintf("%s/%s", g.Host, g.Path)
+}
+
+// ParseGitSource parses a git source string into a GitSource.
+// Supports formats like:
+//   - git:github.com/user/repo
+//   - git:github.com/user/repo@v1.0.0
+//   - https://github.com/user/repo
+//   - https://github.com/user/repo@v1.0.0
+//   - ssh://git@github.com/user/repo
+//   - git@github.com:user/repo
+//   - github.com/user/repo (shorthand, defaults to https)
+func ParseGitSource(source string) (*GitSource, error) {
+	source = strings.TrimSpace(source)
+
+	// Check for @ref suffix
+	ref := ""
+	pinned := false
+	if atIdx := strings.LastIndex(source, "@"); atIdx > 0 {
+		// Make sure it's not part of the protocol (e.g., @ in ssh://git@)
+		after := source[atIdx+1:]
+		if !strings.Contains(after, "/") && !strings.Contains(after, ":") {
+			ref = after
+			pinned = true
+			source = source[:atIdx]
+		}
+	}
+
+	// Handle git: prefix
+	source, _ = strings.CutPrefix(source, "git:")
+
+	var repo, host, path string
+
+	// Handle explicit URLs
+	if strings.HasPrefix(source, "http://") || strings.HasPrefix(source, "https://") {
+		u, err := url.Parse(source)
+		if err != nil {
+			return nil, fmt.Errorf("invalid URL: %w", err)
+		}
+		host = u.Host
+		path = strings.TrimPrefix(u.Path, "/")
+		path, _ = strings.CutSuffix(path, ".git")
+		repo = source
+		if !strings.HasSuffix(repo, ".git") {
+			repo += ".git"
+		}
+	} else if strings.HasPrefix(source, "ssh://") {
+		u, err := url.Parse(source)
+		if err != nil {
+			return nil, fmt.Errorf("invalid SSH URL: %w", err)
+		}
+		host = u.Host
+		path = strings.TrimPrefix(u.Path, "/")
+		path, _ = strings.CutSuffix(path, ".git")
+		repo = source
+	} else if strings.HasPrefix(source, "git@") {
+		// SSH shorthand: git@github.com:user/repo
+		parts := strings.SplitN(source, ":", 2)
+		if len(parts) != 2 {
+			return nil, fmt.Errorf("invalid SSH shorthand format")
+		}
+		host = strings.TrimPrefix(parts[0], "git@")
+		path = parts[1]
+		path, _ = strings.CutSuffix(path, ".git")
+		repo = source
+	} else if strings.HasPrefix(source, "github.com/") || strings.HasPrefix(source, "gitlab.com/") || strings.HasPrefix(source, "bitbucket.org/") {
+		// Shorthand for known hosts: host/path
+		parts := strings.SplitN(source, "/", 2)
+		if len(parts) != 2 {
+			return nil, fmt.Errorf("invalid shorthand format, expected host/path")
+		}
+		host = parts[0]
+		path = parts[1]
+		repo = fmt.Sprintf("https://%s/%s.git", host, path)
+	} else if strings.HasPrefix(source, ".") || strings.HasPrefix(source, "/") || strings.HasPrefix(source, "~") {
+		// Local paths are not supported
+		return nil, fmt.Errorf("local paths not supported, use explicit extension path with -e flag")
+	} else {
+		// Generic shorthand: host/user/repo (3+ path segments)
+		parts := strings.Split(source, "/")
+		if len(parts) >= 3 {
+			host = parts[0]
+			path = strings.Join(parts[1:], "/")
+			repo = fmt.Sprintf("https://%s/%s.git", host, path)
+		} else {
+			return nil, fmt.Errorf("unrecognized source format: %s", source)
+		}
+	}
+
+	return &GitSource{
+		Repo:   repo,
+		Host:   host,
+		Path:   path,
+		Ref:    ref,
+		Pinned: pinned,
+	}, nil
+}
+
+// Installer handles installing, updating, and removing git-based extensions.
+type Installer struct {
+	// Global packages root: $XDG_DATA_HOME/kit/git/ (default ~/.local/share/kit/git/)
+	globalGitRoot string
+	// Project packages root: .kit/git/
+	projectGitRoot string
+}
+
+// NewInstaller creates a new Installer.
+func NewInstaller(projectDir string) *Installer {
+	return &Installer{
+		globalGitRoot:  globalGitInstallRoot(),
+		projectGitRoot: filepath.Join(projectDir, ".kit", "git"),
+	}
+}
+
+// Install clones a git repository to the appropriate scope.
+func (i *Installer) Install(source *GitSource, scope InstallScope) error {
+	targetDir := i.getInstallPath(source, scope)
+
+	// Check if already installed
+	if _, err := os.Stat(targetDir); err == nil {
+		return fmt.Errorf("extension already installed at %s", targetDir)
+	}
+
+	// Ensure parent directory exists
+	if err := os.MkdirAll(filepath.Dir(targetDir), 0755); err != nil {
+		return fmt.Errorf("creating parent directory: %w", err)
+	}
+
+	// Clone the repository
+	cmd := exec.Command("git", "clone", "--depth=1", source.Repo, targetDir)
+	if output, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("git clone failed: %w\n%s", err, string(output))
+	}
+
+	// Checkout specific ref if pinned
+	if source.Pinned && source.Ref != "" {
+		checkoutCmd := exec.Command("git", "checkout", source.Ref)
+		checkoutCmd.Dir = targetDir
+		if output, err := checkoutCmd.CombinedOutput(); err != nil {
+			// Clean up on failed checkout
+			_ = os.RemoveAll(targetDir)
+			return fmt.Errorf("git checkout failed: %w\n%s", err, string(output))
+		}
+	}
+
+	// Validate that the package contains valid extensions
+	if err := i.validatePackage(targetDir); err != nil {
+		_ = os.RemoveAll(targetDir)
+		return fmt.Errorf("validation failed: %w", err)
+	}
+
+	// Add to manifest
+	entry := ManifestEntry{
+		Source:    source.String(),
+		Repo:      source.Repo,
+		Host:      source.Host,
+		Path:      source.Path,
+		Ref:       source.Ref,
+		Pinned:    source.Pinned,
+		Scope:     scope,
+		Installed: time.Now(),
+	}
+	if err := i.addToManifest(entry, scope); err != nil {
+		// Don't fail the install, just log the error
+		// The package is installed, manifest update failed
+		return fmt.Errorf("installed but failed to update manifest: %w", err)
+	}
+
+	return nil
+}
+
+// Uninstall removes an installed package.
+func (i *Installer) Uninstall(source *GitSource, scope InstallScope) error {
+	targetDir := i.getInstallPath(source, scope)
+
+	if _, err := os.Stat(targetDir); err != nil {
+		return fmt.Errorf("extension not found at %s", targetDir)
+	}
+
+	// Remove the directory
+	if err := os.RemoveAll(targetDir); err != nil {
+		return fmt.Errorf("removing extension directory: %w", err)
+	}
+
+	// Remove from manifest
+	if err := i.removeFromManifest(source.Identity(), scope); err != nil {
+		return fmt.Errorf("removed but failed to update manifest: %w", err)
+	}
+
+	return nil
+}
+
+// Update fetches and resets a git package to the latest.
+// For pinned packages, this does nothing.
+func (i *Installer) Update(source *GitSource, scope InstallScope) error {
+	if source.Pinned {
+		return nil // Don't update pinned packages
+	}
+
+	targetDir := i.getInstallPath(source, scope)
+
+	if _, err := os.Stat(targetDir); err != nil {
+		return i.Install(source, scope)
+	}
+
+	// Fetch latest
+	fetchCmd := exec.Command("git", "fetch", "--prune", "origin")
+	fetchCmd.Dir = targetDir
+	if output, err := fetchCmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("git fetch failed: %w\n%s", err, string(output))
+	}
+
+	// Reset to tracking branch or origin/HEAD
+	resetCmd := exec.Command("git", "reset", "--hard", "@{upstream}")
+	resetCmd.Dir = targetDir
+	if _, err := resetCmd.CombinedOutput(); err != nil {
+		// Try alternative: set HEAD and reset to origin/HEAD
+		_ = exec.Command("git", "remote", "set-head", "origin", "-a").Run()
+		resetCmd = exec.Command("git", "reset", "--hard", "origin/HEAD")
+		resetCmd.Dir = targetDir
+		if output, err := resetCmd.CombinedOutput(); err != nil {
+			return fmt.Errorf("git reset failed: %w\n%s", err, string(output))
+		}
+	}
+
+	// Clean untracked files
+	cleanCmd := exec.Command("git", "clean", "-fdx")
+	cleanCmd.Dir = targetDir
+	_ = cleanCmd.Run() // Ignore errors - clean is best effort
+
+	// Update manifest timestamp
+	entry := ManifestEntry{
+		Source:    source.String(),
+		Repo:      source.Repo,
+		Host:      source.Host,
+		Path:      source.Path,
+		Ref:       "",
+		Pinned:    false,
+		Scope:     scope,
+		Installed: time.Now(),
+		Updated:   time.Now(),
+	}
+	_ = i.addToManifest(entry, scope) // Best effort - don't fail update if manifest fails
+
+	return nil
+}
+
+// getInstallPath returns the target directory for a source.
+func (i *Installer) getInstallPath(source *GitSource, scope InstallScope) string {
+	root := i.globalGitRoot
+	if scope == ScopeProject {
+		root = i.projectGitRoot
+	}
+	return filepath.Join(root, source.Host, source.Path)
+}
+
+// validatePackage checks that the cloned repo contains valid .go extension files.
+func (i *Installer) validatePackage(dir string) error {
+	// Find all .go files in the directory
+	var goFiles []string
+	err := filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		if !info.IsDir() && strings.HasSuffix(info.Name(), ".go") {
+			goFiles = append(goFiles, path)
+		}
+		return nil
+	})
+	if err != nil {
+		return fmt.Errorf("walking directory: %w", err)
+	}
+
+	if len(goFiles) == 0 {
+		return fmt.Errorf("no .go files found in package")
+	}
+
+	// Try to load the first .go file to validate it's a valid extension
+	// We don't fail if validation fails - the extension might be fine but
+	// have dependencies that aren't available during install time
+	_, err = loadSingleExtension(goFiles[0])
+	if err != nil {
+		// Log but don't fail - the extension might need runtime deps
+		// User can use `kit extensions validate` to check later
+		return nil
+	}
+
+	return nil
+}
+
+// addToManifest adds an entry to the manifest.
+func (i *Installer) addToManifest(entry ManifestEntry, scope InstallScope) error {
+	manifest, err := i.loadManifest(scope)
+	if err != nil {
+		return err
+	}
+
+	// Remove any existing entry with same identity
+	identity := entry.Host + "/" + entry.Path
+	filtered := make([]ManifestEntry, 0, len(manifest.Packages))
+	for _, p := range manifest.Packages {
+		if p.Host+"/"+p.Path != identity {
+			filtered = append(filtered, p)
+		}
+	}
+	filtered = append(filtered, entry)
+	manifest.Packages = filtered
+
+	return i.saveManifest(manifest, scope)
+}
+
+// removeFromManifest removes an entry from the manifest by identity.
+func (i *Installer) removeFromManifest(identity string, scope InstallScope) error {
+	manifest, err := i.loadManifest(scope)
+	if err != nil {
+		return err
+	}
+
+	filtered := make([]ManifestEntry, 0, len(manifest.Packages))
+	for _, p := range manifest.Packages {
+		if p.Host+"/"+p.Path != identity {
+			filtered = append(filtered, p)
+		}
+	}
+	manifest.Packages = filtered
+
+	return i.saveManifest(manifest, scope)
+}
+
+// loadManifest loads the manifest for the given scope.
+func (i *Installer) loadManifest(scope InstallScope) (*Manifest, error) {
+	path := i.manifestPath(scope)
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &Manifest{Packages: []ManifestEntry{}}, nil
+		}
+		return nil, err
+	}
+
+	var manifest Manifest
+	if err := json.Unmarshal(data, &manifest); err != nil {
+		return nil, fmt.Errorf("parsing manifest: %w", err)
+	}
+
+	return &manifest, nil
+}
+
+// saveManifest saves the manifest for the given scope.
+func (i *Installer) saveManifest(manifest *Manifest, scope InstallScope) error {
+	path := i.manifestPath(scope)
+
+	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
+		return fmt.Errorf("creating manifest directory: %w", err)
+	}
+
+	data, err := json.MarshalIndent(manifest, "", "  ")
+	if err != nil {
+		return fmt.Errorf("encoding manifest: %w", err)
+	}
+
+	if err := os.WriteFile(path, data, 0644); err != nil {
+		return fmt.Errorf("writing manifest: %w", err)
+	}
+
+	return nil
+}
+
+// manifestPath returns the path to the manifest file.
+func (i *Installer) manifestPath(scope InstallScope) string {
+	if scope == ScopeProject {
+		return filepath.Join(i.projectGitRoot, "packages.json")
+	}
+	return filepath.Join(i.globalGitRoot, "packages.json")
+}
+
+// globalGitInstallRoot returns the global git install root.
+func globalGitInstallRoot() string {
+	base := os.Getenv("XDG_DATA_HOME")
+	if base == "" {
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return ""
+		}
+		base = filepath.Join(home, ".local", "share")
+	}
+	return filepath.Join(base, "kit", "git")
+}
+
+// GetInstalledPackages returns all installed packages from both scopes.
+func (i *Installer) GetInstalledPackages() ([]ManifestEntry, error) {
+	var all []ManifestEntry
+
+	global, err := i.loadManifest(ScopeGlobal)
+	if err != nil {
+		return nil, fmt.Errorf("loading global manifest: %w", err)
+	}
+	all = append(all, global.Packages...)
+
+	project, err := i.loadManifest(ScopeProject)
+	if err != nil {
+		return nil, fmt.Errorf("loading project manifest: %w", err)
+	}
+	all = append(all, project.Packages...)
+
+	return all, nil
+}
+
+// IsInstalled checks if a package is installed in either scope.
+// Returns (scope, true) if installed, ("", false) otherwise.
+func (i *Installer) IsInstalled(source *GitSource) (InstallScope, bool) {
+	globalPath := i.getInstallPath(source, ScopeGlobal)
+	if _, err := os.Stat(globalPath); err == nil {
+		return ScopeGlobal, true
+	}
+
+	projectPath := i.getInstallPath(source, ScopeProject)
+	if _, err := os.Stat(projectPath); err == nil {
+		return ScopeProject, true
+	}
+
+	return "", false
+}
+
+// PreviewExtensions clones a repo to a temporary directory and scans for extensions.
+// Returns the preview list and the temp directory path (caller should clean up).
+func (i *Installer) PreviewExtensions(source *GitSource) ([]ExtensionPreview, string, error) {
+	// Create temp directory
+	tempDir, err := os.MkdirTemp("", "kit-install-preview-*")
+	if err != nil {
+		return nil, "", fmt.Errorf("creating temp directory: %w", err)
+	}
+
+	// Clone to temp
+	cloneDir := filepath.Join(tempDir, "repo")
+	cmd := exec.Command("git", "clone", "--depth=1", source.Repo, cloneDir)
+	if output, err := cmd.CombinedOutput(); err != nil {
+		_ = os.RemoveAll(tempDir)
+		return nil, "", fmt.Errorf("git clone failed: %w\n%s", err, string(output))
+	}
+
+	// Checkout specific ref if pinned
+	if source.Pinned && source.Ref != "" {
+		checkoutCmd := exec.Command("git", "checkout", source.Ref)
+		checkoutCmd.Dir = cloneDir
+		if output, err := checkoutCmd.CombinedOutput(); err != nil {
+			_ = os.RemoveAll(tempDir)
+			return nil, "", fmt.Errorf("git checkout failed: %w\n%s", err, string(output))
+		}
+	}
+
+	// Scan for extensions
+	previews, err := ScanForExtensions(cloneDir)
+	if err != nil {
+		_ = os.RemoveAll(tempDir)
+		return nil, "", fmt.Errorf("scanning extensions: %w", err)
+	}
+
+	return previews, tempDir, nil
+}
+
+// InstallWithInclude clones a repo and installs only the specified extensions.
+// includePaths are relative paths like "./git/main.go" - if empty, installs all.
+func (i *Installer) InstallWithInclude(source *GitSource, scope InstallScope, includePaths []string) error {
+	// First, do a regular install
+	if err := i.Install(source, scope); err != nil {
+		return err
+	}
+
+	// If specific includes were requested, update the manifest
+	if len(includePaths) > 0 {
+		entry := ManifestEntry{
+			Source:  source.String(),
+			Repo:    source.Repo,
+			Host:    source.Host,
+			Path:    source.Path,
+			Ref:     source.Ref,
+			Pinned:  source.Pinned,
+			Scope:   scope,
+			Include: includePaths,
+		}
+
+		if err := addEntryToManifest(entry, scope); err != nil {
+			return fmt.Errorf("updating manifest with includes: %w", err)
+		}
+	}
+
+	return nil
+}
+
+// CleanupTempDir removes a temporary directory used for preview.
+func CleanupTempDir(tempDir string) {
+	if tempDir != "" {
+		_ = os.RemoveAll(tempDir)
+	}
+}

internal/extensions/installer_test.go

@@ -0,0 +1,392 @@
+package extensions
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestParseGitSource(t *testing.T) {
+	tests := []struct {
+		name       string
+		source     string
+		wantRepo   string
+		wantHost   string
+		wantPath   string
+		wantRef    string
+		wantPinned bool
+		wantErr    bool
+	}{
+		{
+			name:       "github shorthand",
+			source:     "github.com/user/repo",
+			wantRepo:   "https://github.com/user/repo.git",
+			wantHost:   "github.com",
+			wantPath:   "user/repo",
+			wantRef:    "",
+			wantPinned: false,
+		},
+		{
+			name:       "github shorthand with version",
+			source:     "github.com/user/repo@v1.0.0",
+			wantRepo:   "https://github.com/user/repo.git",
+			wantHost:   "github.com",
+			wantPath:   "user/repo",
+			wantRef:    "v1.0.0",
+			wantPinned: true,
+		},
+		{
+			name:       "git prefix shorthand",
+			source:     "git:github.com/user/repo",
+			wantRepo:   "https://github.com/user/repo.git",
+			wantHost:   "github.com",
+			wantPath:   "user/repo",
+			wantRef:    "",
+			wantPinned: false,
+		},
+		{
+			name:       "https URL",
+			source:     "https://github.com/user/repo",
+			wantRepo:   "https://github.com/user/repo.git",
+			wantHost:   "github.com",
+			wantPath:   "user/repo",
+			wantRef:    "",
+			wantPinned: false,
+		},
+		{
+			name:       "https URL with .git suffix",
+			source:     "https://github.com/user/repo.git",
+			wantRepo:   "https://github.com/user/repo.git",
+			wantHost:   "github.com",
+			wantPath:   "user/repo",
+			wantRef:    "",
+			wantPinned: false,
+		},
+		{
+			name:       "ssh shorthand",
+			source:     "git@github.com:user/repo",
+			wantRepo:   "git@github.com:user/repo",
+			wantHost:   "github.com",
+			wantPath:   "user/repo",
+			wantRef:    "",
+			wantPinned: false,
+		},
+		{
+			name:       "ssh URL",
+			source:     "ssh://git@github.com/user/repo",
+			wantRepo:   "ssh://git@github.com/user/repo",
+			wantHost:   "github.com",
+			wantPath:   "user/repo",
+			wantRef:    "",
+			wantPinned: false,
+		},
+		{
+			name:       "gitlab shorthand",
+			source:     "gitlab.com/user/repo",
+			wantRepo:   "https://gitlab.com/user/repo.git",
+			wantHost:   "gitlab.com",
+			wantPath:   "user/repo",
+			wantRef:    "",
+			wantPinned: false,
+		},
+		{
+			name:       "bitbucket shorthand",
+			source:     "bitbucket.org/user/repo",
+			wantRepo:   "https://bitbucket.org/user/repo.git",
+			wantHost:   "bitbucket.org",
+			wantPath:   "user/repo",
+			wantRef:    "",
+			wantPinned: false,
+		},
+		{
+			name:       "generic host",
+			source:     "gitea.example.com/user/repo",
+			wantRepo:   "https://gitea.example.com/user/repo.git",
+			wantHost:   "gitea.example.com",
+			wantPath:   "user/repo",
+			wantRef:    "",
+			wantPinned: false,
+		},
+		{
+			name:       "with branch ref",
+			source:     "github.com/user/repo@main",
+			wantRepo:   "https://github.com/user/repo.git",
+			wantHost:   "github.com",
+			wantPath:   "user/repo",
+			wantRef:    "main",
+			wantPinned: true,
+		},
+		{
+			name:       "with commit ref",
+			source:     "github.com/user/repo@abc1234",
+			wantRepo:   "https://github.com/user/repo.git",
+			wantHost:   "github.com",
+			wantPath:   "user/repo",
+			wantRef:    "abc1234",
+			wantPinned: true,
+		},
+		{
+			name:    "local path should error",
+			source:  "./local/path",
+			wantErr: true,
+		},
+		{
+			name:    "absolute path should error",
+			source:  "/absolute/path",
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ParseGitSource(tt.source)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ParseGitSource() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if err != nil {
+				return
+			}
+			if got.Repo != tt.wantRepo {
+				t.Errorf("ParseGitSource() Repo = %v, want %v", got.Repo, tt.wantRepo)
+			}
+			if got.Host != tt.wantHost {
+				t.Errorf("ParseGitSource() Host = %v, want %v", got.Host, tt.wantHost)
+			}
+			if got.Path != tt.wantPath {
+				t.Errorf("ParseGitSource() Path = %v, want %v", got.Path, tt.wantPath)
+			}
+			if got.Ref != tt.wantRef {
+				t.Errorf("ParseGitSource() Ref = %v, want %v", got.Ref, tt.wantRef)
+			}
+			if got.Pinned != tt.wantPinned {
+				t.Errorf("ParseGitSource() Pinned = %v, want %v", got.Pinned, tt.wantPinned)
+			}
+		})
+	}
+}
+
+func TestGitSourceIdentity(t *testing.T) {
+	source := &GitSource{
+		Host: "github.com",
+		Path: "user/repo",
+	}
+	if got := source.Identity(); got != "github.com/user/repo" {
+		t.Errorf("Identity() = %v, want %v", got, "github.com/user/repo")
+	}
+}
+
+func TestGitSourceString(t *testing.T) {
+	tests := []struct {
+		name   string
+		source GitSource
+		want   string
+	}{
+		{
+			name: "unpinned",
+			source: GitSource{
+				Host:   "github.com",
+				Path:   "user/repo",
+				Pinned: false,
+			},
+			want: "git:github.com/user/repo",
+		},
+		{
+			name: "pinned",
+			source: GitSource{
+				Host:   "github.com",
+				Path:   "user/repo",
+				Ref:    "v1.0.0",
+				Pinned: true,
+			},
+			want: "git:github.com/user/repo@v1.0.0",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := tt.source.String(); got != tt.want {
+				t.Errorf("String() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestInstallerGetInstallPath(t *testing.T) {
+	tempDir := t.TempDir()
+	installer := NewInstaller(tempDir)
+
+	source := &GitSource{
+		Host: "github.com",
+		Path: "user/repo",
+	}
+
+	// Test global scope
+	globalPath := installer.getInstallPath(source, ScopeGlobal)
+	if !filepath.IsAbs(globalPath) {
+		t.Error("Global install path should be absolute")
+	}
+
+	// Test project scope
+	projectPath := installer.getInstallPath(source, ScopeProject)
+	expectedProjectPath := filepath.Join(tempDir, ".kit", "git", "github.com", "user", "repo")
+	if projectPath != expectedProjectPath {
+		t.Errorf("Project path = %v, want %v", projectPath, expectedProjectPath)
+	}
+}
+
+func TestManifestEntryIdentity(t *testing.T) {
+	entry := ManifestEntry{
+		Host: "github.com",
+		Path: "user/repo",
+	}
+	if got := entry.Identity(); got != "github.com/user/repo" {
+		t.Errorf("Identity() = %v, want %v", got, "github.com/user/repo")
+	}
+}
+
+func TestLoadAndSaveManifest(t *testing.T) {
+	tempDir := t.TempDir()
+	manifestPath := filepath.Join(tempDir, "packages.json")
+
+	// Test loading non-existent manifest
+	manifest, err := loadManifestFromPath(manifestPath)
+	if err != nil {
+		t.Fatalf("loadManifestFromPath() error = %v", err)
+	}
+	if len(manifest.Packages) != 0 {
+		t.Errorf("Expected empty packages, got %d", len(manifest.Packages))
+	}
+
+	// Create a manifest
+	manifest = &Manifest{
+		Packages: []ManifestEntry{
+			{
+				Source: "git:github.com/user/repo",
+				Repo:   "https://github.com/user/repo.git",
+				Host:   "github.com",
+				Path:   "user/repo",
+				Pinned: false,
+				Scope:  ScopeGlobal,
+			},
+		},
+	}
+
+	// Save it
+	err = saveManifestToPath(manifest, manifestPath)
+	if err != nil {
+		t.Fatalf("saveManifestToPath() error = %v", err)
+	}
+
+	// Load it back
+	loaded, err := loadManifestFromPath(manifestPath)
+	if err != nil {
+		t.Fatalf("loadManifestFromPath() error = %v", err)
+	}
+	if len(loaded.Packages) != 1 {
+		t.Errorf("Expected 1 package, got %d", len(loaded.Packages))
+	}
+	if loaded.Packages[0].Host != "github.com" {
+		t.Errorf("Expected host github.com, got %s", loaded.Packages[0].Host)
+	}
+}
+
+func TestAddAndRemoveFromManifest(t *testing.T) {
+	tempDir := t.TempDir()
+
+	// Set up environment for manifest path
+	if err := os.Setenv("XDG_DATA_HOME", tempDir); err != nil {
+		t.Fatalf("Setenv() error = %v", err)
+	}
+	defer func() {
+		if err := os.Unsetenv("XDG_DATA_HOME"); err != nil {
+			t.Logf("Unsetenv() error = %v", err)
+		}
+	}()
+
+	// The manifest path when XDG_DATA_HOME is set
+	manifestPath := filepath.Join(tempDir, "kit", "git", "packages.json")
+
+	// Add an entry
+	entry := ManifestEntry{
+		Source: "git:github.com/user/repo",
+		Host:   "github.com",
+		Path:   "user/repo",
+		Scope:  ScopeGlobal,
+	}
+
+	err := addEntryToManifest(entry, ScopeGlobal)
+	if err != nil {
+		t.Fatalf("addEntryToManifest() error = %v", err)
+	}
+
+	// Verify it was added
+	manifest, err := loadManifestFromPath(manifestPath)
+	if err != nil {
+		t.Fatalf("loadManifestFromPath() error = %v", err)
+	}
+	if len(manifest.Packages) != 1 {
+		t.Errorf("Expected 1 package, got %d", len(manifest.Packages))
+	}
+
+	// Remove it
+	err = removeEntryFromManifest("github.com/user/repo", ScopeGlobal)
+	if err != nil {
+		t.Fatalf("removeEntryFromManifest() error = %v", err)
+	}
+
+	// Verify it was removed
+	manifest, err = loadManifestFromPath(manifestPath)
+	if err != nil {
+		t.Fatalf("loadManifestFromPath() error = %v", err)
+	}
+	if len(manifest.Packages) != 0 {
+		t.Errorf("Expected 0 packages, got %d", len(manifest.Packages))
+	}
+}
+
+func TestFindInManifest(t *testing.T) {
+	tempDir := t.TempDir()
+	if err := os.Setenv("XDG_DATA_HOME", tempDir); err != nil {
+		t.Fatalf("Setenv() error = %v", err)
+	}
+	defer func() {
+		if err := os.Unsetenv("XDG_DATA_HOME"); err != nil {
+			t.Logf("Unsetenv() error = %v", err)
+		}
+	}()
+
+	// Add an entry to global manifest
+	entry := ManifestEntry{
+		Source: "git:github.com/user/repo",
+		Host:   "github.com",
+		Path:   "user/repo",
+		Scope:  ScopeGlobal,
+	}
+
+	err := addEntryToManifest(entry, ScopeGlobal)
+	if err != nil {
+		t.Fatalf("addEntryToManifest() error = %v", err)
+	}
+
+	// Find it
+	found, scope, err := FindInManifest("github.com/user/repo")
+	if err != nil {
+		t.Fatalf("FindInManifest() error = %v", err)
+	}
+	if found == nil {
+		t.Fatal("Expected to find entry, got nil")
+	}
+	if scope != ScopeGlobal {
+		t.Errorf("Expected scope global, got %s", scope)
+	}
+
+	// Try to find non-existent
+	notFound, _, err := FindInManifest("github.com/other/repo")
+	if err != nil {
+		t.Fatalf("FindInManifest() error = %v", err)
+	}
+	if notFound != nil {
+		t.Error("Expected nil for non-existent entry")
+	}
+}

internal/extensions/loader.go

@@ -71,12 +71,24 @@ func discoverExtensionPaths(extraPaths []string) []string {
 		add(p)
 	}
 
+	// Global installed git packages: $XDG_DATA_HOME/kit/git/
+	globalGitDir := globalGitInstallRoot()
+	for _, p := range findExtensionsInGitPackages(globalGitDir) {
+		add(p)
+	}
+
 	// Project-local extensions: .kit/extensions/
 	localDir := filepath.Join(".kit", "extensions")
 	for _, p := range findExtensionsInDir(localDir) {
 		add(p)
 	}
 
+	// Project-local installed git packages: .kit/git/
+	projectGitDir := filepath.Join(".kit", "git")
+	for _, p := range findExtensionsInGitPackages(projectGitDir) {
+		add(p)
+	}
+
 	// Explicit paths (highest precedence)
 	for _, p := range extraPaths {
 		info, err := os.Stat(p)
@@ -123,6 +135,219 @@ func findExtensionsInDir(dir string) []string {
 	return results
 }
 
+// findExtensionsInRepo scans a git repository for extensions using opinionated conventions.
+// Extensions are ONLY recognized in:
+//  1. Root-level *.go files
+//  2. Files in examples/extensions/ or examples/ext/ subdirectories
+//  3. Files in any top-level ext/ directory
+//  4. Files in any subdirectory that ends in -ext/ or -extensions/
+//
+// Everything else (cmd/, internal/, pkg/, etc.) is ignored.
+func findExtensionsInRepo(repoPath string) []string {
+	var results []string
+	multiFileDirs := make(map[string]bool)
+
+	_ = filepath.Walk(repoPath, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		relPath, _ := filepath.Rel(repoPath, path)
+		relPath = filepath.ToSlash(relPath)
+
+		// Skip directories we know don't contain extensions
+		if info.IsDir() {
+			switch info.Name() {
+			case ".git", ".github", "node_modules", "vendor", "dist", "build":
+				return filepath.SkipDir
+			}
+
+			// Skip internal code directories
+			if strings.HasPrefix(relPath, "internal/") ||
+				strings.HasPrefix(relPath, "cmd/") ||
+				strings.HasPrefix(relPath, "pkg/") ||
+				strings.HasPrefix(relPath, "test/") ||
+				strings.HasPrefix(relPath, "tests/") {
+				return filepath.SkipDir
+			}
+
+			// Root directory - scan it
+			if relPath == "." {
+				return nil
+			}
+
+			base := info.Name()
+			isExtDir := base == "extensions" || base == "ext" ||
+				strings.HasSuffix(base, "-extensions") || strings.HasSuffix(base, "-ext")
+
+			isExamplesSubdir := relPath == "examples" || strings.HasPrefix(relPath, "examples/")
+
+			if !isExtDir && !isExamplesSubdir {
+				mainPath := filepath.Join(path, "main.go")
+				if _, err := os.Stat(mainPath); err == nil {
+					if relPath == base { // Top-level directory
+						if !multiFileDirs[relPath] {
+							multiFileDirs[relPath] = true
+							results = append(results, mainPath)
+						}
+						return filepath.SkipDir
+					}
+					if isExamplesSubdir || isExtDir {
+						if !multiFileDirs[relPath] {
+							multiFileDirs[relPath] = true
+							results = append(results, mainPath)
+						}
+						return filepath.SkipDir
+					}
+				}
+				return filepath.SkipDir
+			}
+
+			// Check for main.go
+			mainPath := filepath.Join(path, "main.go")
+			if _, err := os.Stat(mainPath); err == nil {
+				if !multiFileDirs[relPath] {
+					multiFileDirs[relPath] = true
+					results = append(results, mainPath)
+				}
+				return filepath.SkipDir
+			}
+
+			return nil
+		}
+
+		// It's a file
+		if !strings.HasSuffix(info.Name(), ".go") {
+			return nil
+		}
+
+		if info.Name() == "main.go" {
+			return nil
+		}
+
+		parentDir := filepath.Dir(relPath)
+		if parentDir == "." {
+			// Root-level .go file - valid extension
+			results = append(results, path)
+			return nil
+		}
+
+		// Must be in valid extension directory
+		isValidExtDir := false
+		if strings.HasPrefix(parentDir, "examples/extensions/") ||
+			parentDir == "examples/extensions" {
+			isValidExtDir = true
+		} else if strings.HasPrefix(parentDir, "examples/ext/") ||
+			parentDir == "examples/ext" {
+			isValidExtDir = true
+		} else if strings.HasPrefix(parentDir, "ext/") ||
+			parentDir == "ext" {
+			isValidExtDir = true
+		} else if strings.Contains(parentDir, "-extensions/") ||
+			strings.HasSuffix(parentDir, "-extensions") {
+			isValidExtDir = true
+		} else if strings.Contains(parentDir, "-ext/") ||
+			strings.HasSuffix(parentDir, "-ext") {
+			isValidExtDir = true
+		}
+
+		if !isValidExtDir {
+			return nil
+		}
+
+		results = append(results, path)
+		return nil
+	})
+
+	return results
+}
+
+// Each git package is stored at <gitRoot>/<host>/<owner>/<repo>/ and can contain
+// .go files or a main.go in subdirectories.
+// If a package has a manifest with Include field, only those paths are loaded.
+func findExtensionsInGitPackages(gitRoot string) []string {
+	info, err := os.Stat(gitRoot)
+	if err != nil || !info.IsDir() {
+		return nil
+	}
+
+	var results []string
+
+	// Load the manifest if it exists
+	manifestPath := filepath.Join(gitRoot, "packages.json")
+	manifest, _ := loadManifestFromPath(manifestPath)
+	// Build a map of package identity -> include list
+	includeMap := make(map[string][]string)
+	if manifest != nil {
+		for _, entry := range manifest.Packages {
+			if len(entry.Include) > 0 {
+				identity := fmt.Sprintf("%s/%s", entry.Host, entry.Path)
+				includeMap[identity] = entry.Include
+			}
+		}
+	}
+
+	// Walk through host directories (e.g., github.com/)
+	hosts, err := os.ReadDir(gitRoot)
+	if err != nil {
+		return nil
+	}
+
+	for _, host := range hosts {
+		if !host.IsDir() {
+			continue
+		}
+		hostPath := filepath.Join(gitRoot, host.Name())
+
+		// Walk through owner directories (e.g., github.com/user/)
+		owners, err := os.ReadDir(hostPath)
+		if err != nil {
+			continue
+		}
+
+		for _, owner := range owners {
+			if !owner.IsDir() {
+				continue
+			}
+			ownerPath := filepath.Join(hostPath, owner.Name())
+
+			// Walk through repo directories (e.g., github.com/user/repo/)
+			repos, err := os.ReadDir(ownerPath)
+			if err != nil {
+				continue
+			}
+
+			for _, repo := range repos {
+				if !repo.IsDir() {
+					continue
+				}
+				repoPath := filepath.Join(ownerPath, repo.Name())
+
+				// Check if there's an include filter for this package
+				identity := fmt.Sprintf("%s/%s/%s", host.Name(), owner.Name(), repo.Name())
+				includes, hasFilter := includeMap[identity]
+
+				if hasFilter {
+					// Only include specific paths
+					for _, include := range includes {
+						// Convert relative path to absolute
+						include = strings.TrimPrefix(include, "./")
+						fullPath := filepath.Join(repoPath, filepath.FromSlash(include))
+						if _, err := os.Stat(fullPath); err == nil {
+							results = append(results, fullPath)
+						}
+					}
+				} else {
+					// Find all extensions within this repo using convention-based scanning
+					results = append(results, findExtensionsInRepo(repoPath)...)
+				}
+			}
+		}
+	}
+
+	return results
+}
+
 // globalExtensionsDir returns the global extensions directory, respecting
 // $XDG_CONFIG_HOME. Defaults to ~/.config/kit/extensions.
 func globalExtensionsDir() string {
@@ -214,6 +439,12 @@ func loadSingleExtension(path string) (*LoadedExtension, error) {
 				return nil
 			})
 		},
+		onToolOutput: func(h func(ToolOutputEvent, Context)) {
+			reg(ToolOutput, func(e Event, c Context) Result {
+				h(e.(ToolOutputEvent), c)
+				return nil
+			})
+		},
 		onToolResult: func(h func(ToolResultEvent, Context) *ToolResultResult) {
 			reg(ToolResult, func(e Event, c Context) Result {
 				r := h(e.(ToolResultEvent), c)
@@ -283,6 +514,48 @@ func loadSingleExtension(path string) (*LoadedExtension, error) {
 				return nil
 			})
 		},
+		onModelChange: func(h func(ModelChangeEvent, Context)) {
+			reg(ModelChange, func(e Event, c Context) Result {
+				h(e.(ModelChangeEvent), c)
+				return nil
+			})
+		},
+		onContextPrepare: func(h func(ContextPrepareEvent, Context) *ContextPrepareResult) {
+			reg(ContextPrepare, func(e Event, c Context) Result {
+				r := h(e.(ContextPrepareEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
+		onBeforeFork: func(h func(BeforeForkEvent, Context) *BeforeForkResult) {
+			reg(BeforeFork, func(e Event, c Context) Result {
+				r := h(e.(BeforeForkEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
+		onBeforeSessionSwitch: func(h func(BeforeSessionSwitchEvent, Context) *BeforeSessionSwitchResult) {
+			reg(BeforeSessionSwitch, func(e Event, c Context) Result {
+				r := h(e.(BeforeSessionSwitchEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
+		onBeforeCompact: func(h func(BeforeCompactEvent, Context) *BeforeCompactResult) {
+			reg(BeforeCompact, func(e Event, c Context) Result {
+				r := h(e.(BeforeCompactEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
 		registerToolFn: func(tool ToolDef) {
 			ext.Tools = append(ext.Tools, tool)
 		},
@@ -292,6 +565,39 @@ func loadSingleExtension(path string) (*LoadedExtension, error) {
 		registerToolRendererFn: func(config ToolRenderConfig) {
 			ext.ToolRenderers = append(ext.ToolRenderers, config)
 		},
+		registerMessageRendererFn: func(config MessageRendererConfig) {
+			ext.MessageRenderers = append(ext.MessageRenderers, config)
+		},
+		onCustomEvent: func(name string, handler func(string)) {
+			if ext.CustomEventHandlers == nil {
+				ext.CustomEventHandlers = make(map[string][]func(string))
+			}
+			ext.CustomEventHandlers[name] = append(ext.CustomEventHandlers[name], handler)
+		},
+		registerOption: func(opt OptionDef) {
+			ext.Options = append(ext.Options, opt)
+		},
+		registerShortcutFn: func(def ShortcutDef, handler func(Context)) {
+			ext.Shortcuts = append(ext.Shortcuts, ShortcutEntry{Def: def, Handler: handler})
+		},
+		onSubagentStart: func(h func(SubagentStartEvent, Context)) {
+			reg(SubagentStart, func(e Event, c Context) Result {
+				h(e.(SubagentStartEvent), c)
+				return nil
+			})
+		},
+		onSubagentChunk: func(h func(SubagentChunkEvent, Context)) {
+			reg(SubagentChunk, func(e Event, c Context) Result {
+				h(e.(SubagentChunkEvent), c)
+				return nil
+			})
+		},
+		onSubagentEnd: func(h func(SubagentEndEvent, Context)) {
+			reg(SubagentEnd, func(e Event, c Context) Result {
+				h(e.(SubagentEndEvent), c)
+				return nil
+			})
+		},
 	}
 
 	// Call Init — the extension registers its handlers, tools, commands.

internal/extensions/loader_test.go

@@ -304,6 +304,15 @@ func Init(api ext.API) {
 func TestLoadExtensions_SkipsBadFiles(t *testing.T) {
 	dir := t.TempDir()
 
+	// Isolate from host environment so globally-installed extensions
+	// are not discovered alongside the test fixtures.
+	isolated := t.TempDir()
+	t.Setenv("XDG_CONFIG_HOME", filepath.Join(isolated, "config"))
+	t.Setenv("XDG_DATA_HOME", filepath.Join(isolated, "data"))
+	origWd, _ := os.Getwd()
+	_ = os.Chdir(isolated)
+	t.Cleanup(func() { _ = os.Chdir(origWd) })
+
 	// Good extension
 	good := `package main
 import "kit/ext"

internal/extensions/manifest.go

@@ -0,0 +1,398 @@
+package extensions
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"golang.org/x/text/cases"
+	"golang.org/x/text/language"
+)
+
+// Manifest tracks installed git packages.
+type Manifest struct {
+	Packages []ManifestEntry `json:"packages"`
+}
+
+// ManifestEntry represents a single installed package.
+type ManifestEntry struct {
+	// Source is the canonical string representation (e.g., "git:github.com/user/repo@v1.0.0")
+	Source string `json:"source"`
+	// Repo is the clone URL
+	Repo string `json:"repo"`
+	// Host is the git host (e.g., github.com)
+	Host string `json:"host"`
+	// Path is the path on the host (e.g., user/repo)
+	Path string `json:"path"`
+	// Ref is the optional pinned ref (tag/branch/commit)
+	Ref string `json:"ref,omitempty"`
+	// Pinned indicates if the ref is pinned
+	Pinned bool `json:"pinned"`
+	// Scope is where the package is installed (global or project)
+	Scope InstallScope `json:"scope"`
+	// Installed is when the package was first installed
+	Installed time.Time `json:"installed"`
+	// Updated is when the package was last updated (only for unpinned, zero time means never updated)
+	Updated time.Time `json:"updated,omitzero"`
+	// Include is a list of relative paths to extensions that should be loaded.
+	// If empty, all extensions in the package are loaded.
+	// Paths are relative to the package root (e.g., "./git/main.go", "./weather.go")
+	Include []string `json:"include,omitempty"`
+}
+
+// Identity returns the normalized identity for deduplication.
+func (e ManifestEntry) Identity() string {
+	return fmt.Sprintf("%s/%s", e.Host, e.Path)
+}
+
+// loadManifest loads the manifest from the given scope.
+func loadManifestFromScope(scope InstallScope) (*Manifest, error) {
+	path := manifestPathForScope(scope)
+	return loadManifestFromPath(path)
+}
+
+// loadManifestFromPath loads a manifest from a specific file path.
+func loadManifestFromPath(path string) (*Manifest, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &Manifest{Packages: []ManifestEntry{}}, nil
+		}
+		return nil, fmt.Errorf("reading manifest: %w", err)
+	}
+
+	var manifest Manifest
+	if err := json.Unmarshal(data, &manifest); err != nil {
+		return nil, fmt.Errorf("parsing manifest: %w", err)
+	}
+
+	return &manifest, nil
+}
+
+// saveManifestToScope saves the manifest to the given scope.
+func saveManifestToScope(manifest *Manifest, scope InstallScope) error {
+	path := manifestPathForScope(scope)
+	return saveManifestToPath(manifest, path)
+}
+
+// saveManifestToPath saves a manifest to a specific file path.
+func saveManifestToPath(manifest *Manifest, path string) error {
+	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
+		return fmt.Errorf("creating manifest directory: %w", err)
+	}
+
+	data, err := json.MarshalIndent(manifest, "", "  ")
+	if err != nil {
+		return fmt.Errorf("encoding manifest: %w", err)
+	}
+
+	if err := os.WriteFile(path, data, 0644); err != nil {
+		return fmt.Errorf("writing manifest: %w", err)
+	}
+
+	return nil
+}
+
+// manifestPathForScope returns the manifest file path for a scope.
+func manifestPathForScope(scope InstallScope) string {
+	if scope == ScopeProject {
+		return filepath.Join(".kit", "git", "packages.json")
+	}
+
+	base := os.Getenv("XDG_DATA_HOME")
+	if base == "" {
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return ""
+		}
+		base = filepath.Join(home, ".local", "share")
+	}
+	return filepath.Join(base, "kit", "git", "packages.json")
+}
+
+// GetGlobalManifest returns the global manifest.
+func GetGlobalManifest() (*Manifest, error) {
+	return loadManifestFromScope(ScopeGlobal)
+}
+
+// GetProjectManifest returns the project manifest.
+func GetProjectManifest() (*Manifest, error) {
+	return loadManifestFromScope(ScopeProject)
+}
+
+// addEntryToManifest adds or replaces an entry in the manifest for a scope.
+func addEntryToManifest(entry ManifestEntry, scope InstallScope) error {
+	manifest, err := loadManifestFromScope(scope)
+	if err != nil {
+		return err
+	}
+
+	// Remove any existing entry with same identity
+	identity := entry.Identity()
+	filtered := make([]ManifestEntry, 0, len(manifest.Packages))
+	for _, p := range manifest.Packages {
+		if p.Identity() != identity {
+			filtered = append(filtered, p)
+		}
+	}
+	filtered = append(filtered, entry)
+	manifest.Packages = filtered
+
+	return saveManifestToScope(manifest, scope)
+}
+
+// removeEntryFromManifest removes an entry by identity from the manifest for a scope.
+func removeEntryFromManifest(identity string, scope InstallScope) error {
+	manifest, err := loadManifestFromScope(scope)
+	if err != nil {
+		return err
+	}
+
+	filtered := make([]ManifestEntry, 0, len(manifest.Packages))
+	for _, p := range manifest.Packages {
+		if p.Identity() != identity {
+			filtered = append(filtered, p)
+		}
+	}
+	manifest.Packages = filtered
+
+	return saveManifestToScope(manifest, scope)
+}
+
+// FindInManifest finds an entry by identity in either global or project manifest.
+// Returns the entry and its scope, or nil if not found.
+func FindInManifest(identity string) (*ManifestEntry, InstallScope, error) {
+	global, err := loadManifestFromScope(ScopeGlobal)
+	if err != nil {
+		return nil, "", fmt.Errorf("loading global manifest: %w", err)
+	}
+	for _, p := range global.Packages {
+		if p.Identity() == identity {
+			return &p, ScopeGlobal, nil
+		}
+	}
+
+	project, err := loadManifestFromScope(ScopeProject)
+	if err != nil {
+		return nil, "", fmt.Errorf("loading project manifest: %w", err)
+	}
+	for _, p := range project.Packages {
+		if p.Identity() == identity {
+			return &p, ScopeProject, nil
+		}
+	}
+
+	return nil, "", nil
+}
+
+// ExtensionPreview represents a discovered extension in a package before installation.
+type ExtensionPreview struct {
+	// Path is the relative path from the package root (e.g., "./git/main.go")
+	Path string `json:"path"`
+	// Name is a display name for the extension (derived from path or metadata)
+	Name string `json:"name"`
+	// Description is an optional description (could be extracted from comments)
+	Description string `json:"description,omitempty"`
+	// IsMain indicates if this is a main.go in a subdirectory
+	IsMain bool `json:"is_main"`
+}
+
+// ScanForExtensions discovers all extensions in a directory using opinionated conventions.
+// Extensions are ONLY recognized in these specific locations:
+//  1. Root-level *.go files
+//  2. Files in examples/extensions/ or examples/ext/ subdirectories
+//  3. Files in any top-level ext/ directory
+//  4. Files in any subdirectory that ends in -ext/ or -extensions/
+//
+// Everything else (cmd/, internal/, pkg/, etc.) is ignored.
+func ScanForExtensions(dir string) ([]ExtensionPreview, error) {
+	info, err := os.Stat(dir)
+	if err != nil || !info.IsDir() {
+		return nil, fmt.Errorf("not a directory: %s", dir)
+	}
+
+	var previews []ExtensionPreview
+	multiFileDirs := make(map[string]bool)
+
+	err = filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		relPath, _ := filepath.Rel(dir, path)
+		relPath = filepath.ToSlash(relPath)
+
+		// Skip directories we know don't contain extensions
+		if info.IsDir() {
+			// Never scan these directories
+			switch info.Name() {
+			case ".git", ".github", "node_modules", "vendor", "dist", "build":
+				return filepath.SkipDir
+			}
+
+			// Skip internal code directories
+			if strings.HasPrefix(relPath, "internal/") ||
+				strings.HasPrefix(relPath, "cmd/") ||
+				strings.HasPrefix(relPath, "pkg/") ||
+				strings.HasPrefix(relPath, "test/") ||
+				strings.HasPrefix(relPath, "tests/") {
+				return filepath.SkipDir
+			}
+
+			// Root directory - scan it
+			if relPath == "." {
+				return nil
+			}
+
+			// Check if this directory is an extension location by name
+			// Pattern: must be named "extensions", "ext", or end with those
+			base := info.Name()
+			isExtDir := base == "extensions" || base == "ext" ||
+				strings.HasSuffix(base, "-extensions") || strings.HasSuffix(base, "-ext")
+
+			// Or check if it's a subdirectory of examples/ that might contain extensions
+			isExamplesSubdir := relPath == "examples" || strings.HasPrefix(relPath, "examples/")
+
+			if !isExtDir && !isExamplesSubdir {
+				// Check for main.go before skipping
+				mainPath := filepath.Join(path, "main.go")
+				if _, err := os.Stat(mainPath); err == nil {
+					// This is a package with main.go at root level
+					if relPath == base { // Top-level directory
+						if !multiFileDirs[relPath] {
+							multiFileDirs[relPath] = true
+							previews = append(previews, ExtensionPreview{
+								Path:   "./" + relPath + "/main.go",
+								Name:   deriveExtensionName(relPath+"/main.go", true),
+								IsMain: true,
+							})
+						}
+						return filepath.SkipDir
+					}
+					// Inside a valid extensions directory
+					if isExamplesSubdir || isExtDir {
+						if !multiFileDirs[relPath] {
+							multiFileDirs[relPath] = true
+							previews = append(previews, ExtensionPreview{
+								Path:   "./" + relPath + "/main.go",
+								Name:   deriveExtensionName(relPath+"/main.go", true),
+								IsMain: true,
+							})
+						}
+						return filepath.SkipDir
+					}
+				}
+
+				// Not an extension location
+				return filepath.SkipDir
+			}
+
+			// Check for main.go in this directory
+			mainPath := filepath.Join(path, "main.go")
+			if _, err := os.Stat(mainPath); err == nil {
+				if !multiFileDirs[relPath] {
+					multiFileDirs[relPath] = true
+					previews = append(previews, ExtensionPreview{
+						Path:   "./" + relPath + "/main.go",
+						Name:   deriveExtensionName(relPath+"/main.go", true),
+						IsMain: true,
+					})
+				}
+				return filepath.SkipDir
+			}
+
+			// Scan this extensions directory
+			return nil
+		}
+
+		// It's a file - check if it's a valid extension
+		if !strings.HasSuffix(info.Name(), ".go") {
+			return nil
+		}
+
+		if info.Name() == "main.go" {
+			return nil // Already handled above
+		}
+
+		// Check if parent is a valid extension location
+		parentDir := filepath.Dir(relPath)
+		if parentDir == "." {
+			// Root-level .go file - valid extension
+			previews = append(previews, ExtensionPreview{
+				Path:   "./" + relPath,
+				Name:   deriveExtensionName(relPath, false),
+				IsMain: false,
+			})
+			return nil
+		}
+
+		// Check if we're in a valid extension directory
+		// Valid locations are:
+		// - examples/extensions/*
+		// - examples/ext/*
+		// - ext/* (top-level)
+		// - Any *-extensions/* or *-ext/* directory
+		isValidExtDir := false
+		if strings.HasPrefix(parentDir, "examples/extensions/") ||
+			parentDir == "examples/extensions" {
+			isValidExtDir = true
+		} else if strings.HasPrefix(parentDir, "examples/ext/") ||
+			parentDir == "examples/ext" {
+			isValidExtDir = true
+		} else if strings.HasPrefix(parentDir, "ext/") ||
+			parentDir == "ext" {
+			isValidExtDir = true
+		} else if strings.Contains(parentDir, "-extensions/") ||
+			strings.HasSuffix(parentDir, "-extensions") {
+			isValidExtDir = true
+		} else if strings.Contains(parentDir, "-ext/") ||
+			strings.HasSuffix(parentDir, "-ext") {
+			isValidExtDir = true
+		}
+
+		if !isValidExtDir {
+			return nil
+		}
+
+		previews = append(previews, ExtensionPreview{
+			Path:   "./" + relPath,
+			Name:   deriveExtensionName(relPath, false),
+			IsMain: false,
+		})
+
+		return nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	return previews, nil
+}
+
+// deriveExtensionName creates a display name from a file path.
+func deriveExtensionName(relPath string, isMain bool) string {
+	// Convert path to a readable name
+	// e.g., "git/main.go" -> "Git Extension"
+	// e.g., "weather.go" -> "Weather"
+
+	dir := filepath.Dir(relPath)
+	base := filepath.Base(relPath)
+
+	if isMain && dir != "." {
+		// Use immediate parent directory name for main.go files
+		name := filepath.Base(dir)
+		name = strings.ReplaceAll(name, "_", " ")
+		name = strings.ReplaceAll(name, "-", " ")
+		return cases.Title(language.English).String(name) + " Extension"
+	}
+
+	// Use filename without extension
+	name := strings.TrimSuffix(base, ".go")
+	name = strings.ReplaceAll(name, "_", " ")
+	name = strings.ReplaceAll(name, "-", " ")
+	return cases.Title(language.English).String(name)
+}

internal/extensions/runner.go

@@ -2,34 +2,52 @@ package extensions
 
 import (
 	"fmt"
+	"os"
 	"sort"
+	"strings"
 	"sync"
 
 	"github.com/charmbracelet/log"
+	"github.com/spf13/viper"
 )
 
 // Runner manages loaded extensions and dispatches events to their handlers
-// sequentially, mirroring Pi's ExtensionRunner. Handlers execute in extension
+// sequentially. Handlers execute in extension
 // load order; for cancellable events the first blocking result wins.
 type Runner struct {
-	extensions   []LoadedExtension
-	ctx          Context
-	widgets      map[string]WidgetConfig // keyed by widget ID
-	header       *HeaderFooterConfig     // nil = no custom header
-	footer       *HeaderFooterConfig     // nil = no custom footer
-	customEditor *EditorConfig           // nil = no custom editor interceptor
-	mu           sync.RWMutex
+	extensions      []LoadedExtension
+	ctx             Context
+	widgets         map[string]WidgetConfig   // keyed by widget ID
+	statusEntries   map[string]StatusBarEntry // keyed by status key
+	header          *HeaderFooterConfig       // nil = no custom header
+	footer          *HeaderFooterConfig       // nil = no custom footer
+	customEditor    *EditorConfig             // nil = no custom editor interceptor
+	uiVisibility    *UIVisibility             // nil = show everything (default)
+	disabledTools   map[string]bool           // nil = all tools enabled
+	customEventSubs map[string][]func(string) // inter-extension event bus
+	optionOverrides map[string]string         // runtime option overrides
+	mu              sync.RWMutex
+}
+
+// ShortcutEntry pairs a shortcut definition with its handler.
+type ShortcutEntry struct {
+	Def     ShortcutDef
+	Handler func(Context)
 }
 
 // LoadedExtension represents a single extension that has been discovered,
 // loaded, and initialised. It holds the registered handlers and any custom
 // tools, commands, or tool renderers the extension provided.
 type LoadedExtension struct {
-	Path          string
-	Handlers      map[EventType][]HandlerFunc
-	Tools         []ToolDef
-	Commands      []CommandDef
-	ToolRenderers []ToolRenderConfig
+	Path                string
+	Handlers            map[EventType][]HandlerFunc
+	Tools               []ToolDef
+	Commands            []CommandDef
+	ToolRenderers       []ToolRenderConfig
+	MessageRenderers    []MessageRendererConfig   // named message renderers
+	CustomEventHandlers map[string][]func(string) // inter-extension event bus
+	Options             []OptionDef               // registered configuration options
+	Shortcuts           []ShortcutEntry           // global keyboard shortcuts
 }
 
 // NewRunner creates a Runner from a set of loaded extensions.
@@ -45,6 +63,13 @@ func (r *Runner) SetContext(ctx Context) {
 	r.ctx = ctx
 }
 
+// GetContext returns a snapshot of the current runtime context. Thread-safe.
+func (r *Runner) GetContext() Context {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	return r.ctx
+}
+
 // HasHandlers returns true if any loaded extension has at least one handler
 // registered for the given event type.
 func (r *Runner) HasHandlers(event EventType) bool {
@@ -121,13 +146,6 @@ func (r *Runner) RegisteredCommands() []CommandDef {
 	return cmds
 }
 
-// GetContext returns the current runtime context. Thread-safe.
-func (r *Runner) GetContext() Context {
-	r.mu.RLock()
-	defer r.mu.RUnlock()
-	return r.ctx
-}
-
 // Extensions returns the loaded extensions for inspection (e.g. CLI list).
 func (r *Runner) Extensions() []LoadedExtension {
 	return r.extensions
@@ -177,6 +195,45 @@ func (r *Runner) GetWidgets(placement WidgetPlacement) []WidgetConfig {
 	return result
 }
 
+// ---------------------------------------------------------------------------
+// Status bar management
+// ---------------------------------------------------------------------------
+
+// SetStatusEntry places or updates a keyed status bar entry. Thread-safe.
+func (r *Runner) SetStatusEntry(entry StatusBarEntry) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if r.statusEntries == nil {
+		r.statusEntries = make(map[string]StatusBarEntry)
+	}
+	r.statusEntries[entry.Key] = entry
+}
+
+// RemoveStatusEntry removes a status bar entry by key. Thread-safe.
+func (r *Runner) RemoveStatusEntry(key string) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	delete(r.statusEntries, key)
+}
+
+// GetStatusEntries returns all status bar entries, sorted by priority
+// (ascending). Thread-safe.
+func (r *Runner) GetStatusEntries() []StatusBarEntry {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	result := make([]StatusBarEntry, 0, len(r.statusEntries))
+	for _, e := range r.statusEntries {
+		result = append(result, e)
+	}
+	sort.Slice(result, func(i, j int) bool {
+		if result[i].Priority != result[j].Priority {
+			return result[i].Priority < result[j].Priority
+		}
+		return result[i].Key < result[j].Key
+	})
+	return result
+}
+
 // ---------------------------------------------------------------------------
 // Header/Footer management
 // ---------------------------------------------------------------------------
@@ -269,6 +326,29 @@ func (r *Runner) GetEditor() *EditorConfig {
 	return &e
 }
 
+// ---------------------------------------------------------------------------
+// UI visibility management
+// ---------------------------------------------------------------------------
+
+// SetUIVisibility updates the UI visibility overrides. Thread-safe.
+func (r *Runner) SetUIVisibility(v UIVisibility) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.uiVisibility = &v
+}
+
+// GetUIVisibility returns the current UI visibility overrides, or nil if
+// none have been set (meaning show everything). Thread-safe.
+func (r *Runner) GetUIVisibility() *UIVisibility {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	if r.uiVisibility == nil {
+		return nil
+	}
+	v := *r.uiVisibility
+	return &v
+}
+
 // ---------------------------------------------------------------------------
 // Tool renderer management
 // ---------------------------------------------------------------------------
@@ -290,6 +370,233 @@ func (r *Runner) GetToolRenderer(toolName string) *ToolRenderConfig {
 	return nil
 }
 
+// ---------------------------------------------------------------------------
+// Message renderer management
+// ---------------------------------------------------------------------------
+
+// GetMessageRenderer returns the named message renderer, or nil if no
+// extension registered a renderer with that name. If multiple extensions
+// register the same name, the last one (by load order) wins.
+func (r *Runner) GetMessageRenderer(name string) *MessageRendererConfig {
+	for i := len(r.extensions) - 1; i >= 0; i-- {
+		for j := len(r.extensions[i].MessageRenderers) - 1; j >= 0; j-- {
+			if r.extensions[i].MessageRenderers[j].Name == name {
+				config := r.extensions[i].MessageRenderers[j]
+				return &config
+			}
+		}
+	}
+	return nil
+}
+
+// ---------------------------------------------------------------------------
+// Hot-reload
+// ---------------------------------------------------------------------------
+
+// Reload replaces the loaded extensions with a fresh set and clears all
+// dynamic state (widgets, status, header/footer, editor, visibility,
+// disabled tools, custom event subscriptions). Option overrides are
+// preserved across reloads since they represent user intent.
+//
+// The caller is responsible for emitting SessionShutdown before calling
+// Reload and SessionStart after.
+func (r *Runner) Reload(exts []LoadedExtension) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.extensions = exts
+	r.widgets = nil
+	r.statusEntries = nil
+	r.header = nil
+	r.footer = nil
+	r.customEditor = nil
+	r.uiVisibility = nil
+	r.disabledTools = nil
+	r.customEventSubs = nil
+	// optionOverrides are intentionally preserved.
+}
+
+// ---------------------------------------------------------------------------
+// Inter-extension event bus
+// ---------------------------------------------------------------------------
+
+// SubscribeCustomEvent registers a handler for a named custom event. Handlers
+// execute in registration order when EmitCustomEvent is called. Thread-safe.
+func (r *Runner) SubscribeCustomEvent(name string, handler func(string)) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if r.customEventSubs == nil {
+		r.customEventSubs = make(map[string][]func(string))
+	}
+	r.customEventSubs[name] = append(r.customEventSubs[name], handler)
+}
+
+// EmitCustomEvent dispatches a named event to all subscribed handlers.
+// Handlers run synchronously in extension load order. Panics are recovered
+// and logged. Thread-safe.
+func (r *Runner) EmitCustomEvent(name, data string) {
+	// Collect handlers: extension-registered (Init-time) + dynamic subs.
+	r.mu.RLock()
+	dynamicHandlers := r.customEventSubs[name]
+	r.mu.RUnlock()
+
+	safeInvoke := func(h func(string)) {
+		defer func() {
+			if rec := recover(); rec != nil {
+				log.Warn("custom event handler panicked",
+					"event", name,
+					"err", fmt.Sprintf("%v", rec))
+			}
+		}()
+		h(data)
+	}
+
+	// Extension-registered handlers first (in load order).
+	for i := range r.extensions {
+		for _, h := range r.extensions[i].CustomEventHandlers[name] {
+			safeInvoke(h)
+		}
+	}
+	// Then dynamic subscriptions.
+	for _, h := range dynamicHandlers {
+		safeInvoke(h)
+	}
+}
+
+// ---------------------------------------------------------------------------
+// Tool management
+// ---------------------------------------------------------------------------
+
+// SetActiveTools restricts the tool set to the named tools. All tools not in
+// the list are disabled. Passing nil or an empty slice re-enables all tools.
+// Thread-safe.
+func (r *Runner) SetActiveTools(names []string) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if len(names) == 0 {
+		r.disabledTools = nil
+		return
+	}
+	active := make(map[string]bool, len(names))
+	for _, n := range names {
+		active[n] = true
+	}
+	r.disabledTools = active // non-nil = only these tools are allowed
+}
+
+// IsToolDisabled returns true if the tool has been disabled via SetActiveTools.
+// Thread-safe.
+func (r *Runner) IsToolDisabled(toolName string) bool {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	if r.disabledTools == nil {
+		return false // no filter = all enabled
+	}
+	return !r.disabledTools[toolName]
+}
+
+// ---------------------------------------------------------------------------
+// Extension options
+// ---------------------------------------------------------------------------
+
+// GetOption resolves a named option value in priority order:
+//  1. Runtime override (via SetOption)
+//  2. Environment variable: KIT_OPT_<NAME> (uppercased, dashes → underscores)
+//  3. Viper config: options.<name>
+//  4. Default value from RegisterOption
+//
+// Returns empty string if the option was never registered.
+// Thread-safe.
+func (r *Runner) GetOption(name string) string {
+	// 1. Runtime override.
+	r.mu.RLock()
+	if v, ok := r.optionOverrides[name]; ok {
+		r.mu.RUnlock()
+		return v
+	}
+	r.mu.RUnlock()
+
+	// 2. Environment variable: KIT_OPT_<NAME>
+	envKey := "KIT_OPT_" + strings.ToUpper(strings.ReplaceAll(name, "-", "_"))
+	if v := os.Getenv(envKey); v != "" {
+		return v
+	}
+
+	// 3. Viper config: options.<name>
+	configKey := "options." + name
+	if v := viper.GetString(configKey); v != "" {
+		return v
+	}
+
+	// 4. Default from registered option defs.
+	for i := range r.extensions {
+		for _, opt := range r.extensions[i].Options {
+			if opt.Name == name {
+				return opt.Default
+			}
+		}
+	}
+
+	return ""
+}
+
+// SetOption stores a runtime override for a named option. This takes highest
+// priority over env vars, config, and defaults. Thread-safe.
+func (r *Runner) SetOption(name, value string) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if r.optionOverrides == nil {
+		r.optionOverrides = make(map[string]string)
+	}
+	r.optionOverrides[name] = value
+}
+
+// RegisteredOptions returns all option definitions from all loaded extensions.
+func (r *Runner) RegisteredOptions() []OptionDef {
+	var opts []OptionDef
+	for i := range r.extensions {
+		opts = append(opts, r.extensions[i].Options...)
+	}
+	return opts
+}
+
+// ---------------------------------------------------------------------------
+// Keyboard shortcuts
+// ---------------------------------------------------------------------------
+
+// GetShortcuts returns all registered keyboard shortcuts as a map of
+// key binding → handler. If multiple extensions register the same key,
+// the last registration wins. Thread-safe (reads extension list which is
+// immutable after loading).
+func (r *Runner) GetShortcuts() map[string]ShortcutEntry {
+	result := make(map[string]ShortcutEntry)
+	for i := range r.extensions {
+		for _, sc := range r.extensions[i].Shortcuts {
+			result[sc.Def.Key] = sc
+		}
+	}
+	if len(result) == 0 {
+		return nil
+	}
+	return result
+}
+
+// RegisteredShortcuts returns all shortcut definitions from all loaded
+// extensions. Used for help/listing commands.
+func (r *Runner) RegisteredShortcuts() []ShortcutDef {
+	var defs []ShortcutDef
+	seen := make(map[string]bool)
+	// Iterate in reverse so last registration for a key wins.
+	for i := len(r.extensions) - 1; i >= 0; i-- {
+		for _, sc := range r.extensions[i].Shortcuts {
+			if !seen[sc.Def.Key] {
+				seen[sc.Def.Key] = true
+				defs = append(defs, sc.Def)
+			}
+		}
+	}
+	return defs
+}
+
 // ---------------------------------------------------------------------------
 // Helpers
 // ---------------------------------------------------------------------------
@@ -311,6 +618,12 @@ func isBlocking(result Result) bool {
 		return r.Block
 	case InputResult:
 		return r.Action == "handled"
+	case BeforeForkResult:
+		return r.Cancel
+	case BeforeSessionSwitchResult:
+		return r.Cancel
+	case BeforeCompactResult:
+		return r.Cancel
 	}
 	return false
 }

internal/extensions/subagent.go

@@ -0,0 +1,377 @@
+// Package extensions provides subagent spawning capabilities for Kit extensions.
+package extensions
+
+import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+// ---------------------------------------------------------------------------
+// Subagent types
+// ---------------------------------------------------------------------------
+
+// SubagentConfig configures a subagent spawn.
+type SubagentConfig struct {
+	// Prompt is the task/instruction for the subagent (required).
+	Prompt string
+
+	// Model overrides the parent's model (e.g. "anthropic/claude-haiku-3-5-20241022").
+	// Empty string uses the parent's current model.
+	Model string
+
+	// SystemPrompt provides domain-specific instructions.
+	// Empty string uses the default system prompt.
+	SystemPrompt string
+
+	// Timeout limits execution time. Zero means 5 minute default.
+	Timeout time.Duration
+
+	// OnOutput streams stderr output chunks as the subagent runs.
+	// Called from a goroutine; must be safe for concurrent use.
+	OnOutput func(chunk string)
+
+	// OnEvent receives real-time events from the subagent's execution:
+	// text chunks, tool calls, tool results, reasoning deltas, etc.
+	// Called synchronously from the subagent's event loop.
+	OnEvent func(SubagentEvent)
+
+	// OnComplete is called when the subagent finishes (success or error).
+	// Called from a goroutine; must be safe for concurrent use.
+	OnComplete func(result SubagentResult)
+
+	// Blocking, when true, makes SpawnSubagent wait for completion and
+	// return the result directly. When false (default), spawns in background
+	// and returns immediately with a handle.
+	Blocking bool
+
+	// NoSession, when true, runs the subagent without persisting a session
+	// file. By default (false), subagent sessions are persisted so they can
+	// be loaded for replay/inspection. Set to true for ephemeral tasks
+	// where session history is not needed.
+	NoSession bool
+
+	// ParentSessionID links the subagent's session to the parent (optional).
+	// When set, the subagent's session header includes a parent reference
+	// so viewers can navigate the session tree.
+	ParentSessionID string
+}
+
+// SubagentEvent carries a real-time event from a running subagent. Extensions
+// use the Type field to determine what happened and read the relevant fields.
+// This is a concrete struct (not an interface) for Yaegi compatibility.
+type SubagentEvent struct {
+	// Type identifies the event: "text", "reasoning", "tool_call",
+	// "tool_result", "tool_execution_start", "tool_execution_end",
+	// "turn_start", "turn_end".
+	Type string
+
+	// Content carries text for "text" and "reasoning" events.
+	Content string
+
+	// ToolCallID is set on tool_call, tool_result, tool_execution_start,
+	// and tool_execution_end events.
+	ToolCallID string
+	// ToolName is set on tool-related events.
+	ToolName string
+	// ToolKind is set on tool-related events.
+	ToolKind string
+	// ToolArgs is set on tool_call events (JSON-encoded).
+	ToolArgs string
+	// ToolResult is set on tool_result events.
+	ToolResult string
+	// IsError is set on tool_result events.
+	IsError bool
+}
+
+// SubagentResult contains the outcome of a subagent execution.
+type SubagentResult struct {
+	// Response is the subagent's final text response.
+	Response string
+
+	// Error is set if the subagent failed (nil on success).
+	Error error
+
+	// ExitCode is the subprocess exit code (0 = success).
+	ExitCode int
+
+	// Elapsed is the total execution time.
+	Elapsed time.Duration
+
+	// Usage contains token usage if available.
+	Usage *SubagentUsage
+
+	// SessionID is the subagent's session identifier, if available.
+	// Populated when the subagent persists its session (requires running
+	// without --no-session). Empty for ephemeral sessions.
+	SessionID string
+}
+
+// SubagentUsage contains token usage from the subagent's run.
+type SubagentUsage struct {
+	InputTokens  int64
+	OutputTokens int64
+}
+
+// SubagentHandle provides control over a running subagent.
+type SubagentHandle struct {
+	// ID is a unique identifier for this subagent instance.
+	ID string
+
+	proc   *os.Process
+	done   chan struct{}
+	result *SubagentResult
+	mu     sync.Mutex
+}
+
+// Kill terminates the subagent process.
+func (h *SubagentHandle) Kill() error {
+	h.mu.Lock()
+	proc := h.proc
+	h.mu.Unlock()
+	if proc != nil {
+		return proc.Kill()
+	}
+	return nil
+}
+
+// Wait blocks until the subagent completes and returns the result.
+func (h *SubagentHandle) Wait() SubagentResult {
+	<-h.done
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	if h.result != nil {
+		return *h.result
+	}
+	return SubagentResult{Error: fmt.Errorf("subagent completed without result")}
+}
+
+// Done returns a channel that closes when the subagent completes.
+func (h *SubagentHandle) Done() <-chan struct{} {
+	return h.done
+}
+
+// ---------------------------------------------------------------------------
+// Internal helpers
+// ---------------------------------------------------------------------------
+
+// subagentJSONOutput matches the JSON envelope produced by `kit --json`.
+type subagentJSONOutput struct {
+	Response   string `json:"response"`
+	StopReason string `json:"stop_reason,omitempty"`
+	SessionID  string `json:"session_id,omitempty"`
+	Usage      *struct {
+		InputTokens  int64 `json:"input_tokens"`
+		OutputTokens int64 `json:"output_tokens"`
+	} `json:"usage,omitempty"`
+}
+
+var subagentCounter uint64
+
+func generateSubagentID() string {
+	n := atomic.AddUint64(&subagentCounter, 1)
+	return fmt.Sprintf("sub-%d-%d", time.Now().UnixNano(), n)
+}
+
+func findKitBinary() string {
+	// Try the current process executable first.
+	if exe, err := os.Executable(); err == nil {
+		if _, err := os.Stat(exe); err == nil {
+			return exe
+		}
+	}
+	// Fall back to PATH lookup.
+	if p, err := exec.LookPath("kit"); err == nil {
+		return p
+	}
+	return "kit"
+}
+
+// ---------------------------------------------------------------------------
+// SpawnSubagent implementation
+// ---------------------------------------------------------------------------
+
+// SpawnSubagent spawns a child Kit instance to perform a task.
+//
+// When config.Blocking is true, blocks until completion and returns the result
+// directly (handle is nil). When false, returns immediately with a handle for
+// monitoring/cancellation.
+//
+// The subagent runs with --json --no-session --no-extensions flags by default,
+// ensuring isolation from the parent's extensions and session state.
+func SpawnSubagent(cfg SubagentConfig) (*SubagentHandle, *SubagentResult, error) {
+	if cfg.Prompt == "" {
+		return nil, nil, fmt.Errorf("prompt is required")
+	}
+
+	timeout := cfg.Timeout
+	if timeout == 0 {
+		timeout = 5 * time.Minute
+	}
+
+	kitBinary := findKitBinary()
+
+	// Build subprocess arguments.
+	args := []string{
+		"--json",
+		"--no-extensions",
+	}
+	if cfg.NoSession {
+		args = append(args, "--no-session")
+	}
+	if cfg.Model != "" {
+		args = append(args, "--model", cfg.Model)
+	}
+
+	// Handle system prompt - write to temp file if provided.
+	var tmpFile *os.File
+	if cfg.SystemPrompt != "" {
+		var err error
+		tmpFile, err = os.CreateTemp("", "kit-subagent-*.txt")
+		if err != nil {
+			return nil, nil, fmt.Errorf("create temp file: %w", err)
+		}
+		if _, err := tmpFile.WriteString(cfg.SystemPrompt); err != nil {
+			_ = tmpFile.Close()
+			_ = os.Remove(tmpFile.Name())
+			return nil, nil, fmt.Errorf("write system prompt: %w", err)
+		}
+		_ = tmpFile.Close()
+		args = append(args, "--system-prompt", tmpFile.Name())
+	}
+
+	// Add the prompt as a positional argument.
+	args = append(args, cfg.Prompt)
+
+	// Create command with timeout context.
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+
+	cmd := exec.CommandContext(ctx, kitBinary, args...)
+	cmd.Env = os.Environ()
+
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		cancel()
+		if tmpFile != nil {
+			_ = os.Remove(tmpFile.Name())
+		}
+		return nil, nil, fmt.Errorf("stdout pipe: %w", err)
+	}
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		cancel()
+		if tmpFile != nil {
+			_ = os.Remove(tmpFile.Name())
+		}
+		return nil, nil, fmt.Errorf("stderr pipe: %w", err)
+	}
+
+	handle := &SubagentHandle{
+		ID:   generateSubagentID(),
+		done: make(chan struct{}),
+	}
+
+	// Start the subprocess.
+	start := time.Now()
+	if err := cmd.Start(); err != nil {
+		cancel()
+		if tmpFile != nil {
+			_ = os.Remove(tmpFile.Name())
+		}
+		return nil, nil, fmt.Errorf("start subprocess: %w", err)
+	}
+
+	handle.mu.Lock()
+	handle.proc = cmd.Process
+	handle.mu.Unlock()
+
+	// Run the subprocess monitoring in a goroutine.
+	go func() {
+		defer close(handle.done)
+		defer cancel()
+		if tmpFile != nil {
+			defer func() { _ = os.Remove(tmpFile.Name()) }()
+		}
+
+		var wg sync.WaitGroup
+		var stdoutBuf strings.Builder
+
+		// Read stderr (live output).
+		wg.Go(func() {
+			scanner := bufio.NewScanner(stderr)
+			scanner.Buffer(make([]byte, 256*1024), 256*1024)
+			for scanner.Scan() {
+				line := scanner.Text()
+				if cfg.OnOutput != nil && strings.TrimSpace(line) != "" {
+					cfg.OnOutput(line + "\n")
+				}
+			}
+		})
+
+		// Read stdout (JSON output).
+		scanner := bufio.NewScanner(stdout)
+		scanner.Buffer(make([]byte, 256*1024), 256*1024)
+		for scanner.Scan() {
+			stdoutBuf.WriteString(scanner.Text() + "\n")
+		}
+
+		wg.Wait()
+		waitErr := cmd.Wait()
+		elapsed := time.Since(start)
+
+		// Build result.
+		result := SubagentResult{Elapsed: elapsed}
+		if waitErr != nil {
+			result.Error = waitErr
+			if exitErr, ok := waitErr.(*exec.ExitError); ok {
+				result.ExitCode = exitErr.ExitCode()
+			} else {
+				result.ExitCode = 1
+			}
+		}
+
+		// Parse JSON output.
+		raw := strings.TrimSpace(stdoutBuf.String())
+		var parsed subagentJSONOutput
+		if raw != "" && json.Unmarshal([]byte(raw), &parsed) == nil {
+			result.Response = parsed.Response
+			result.SessionID = parsed.SessionID
+			if parsed.Usage != nil {
+				result.Usage = &SubagentUsage{
+					InputTokens:  parsed.Usage.InputTokens,
+					OutputTokens: parsed.Usage.OutputTokens,
+				}
+			}
+		} else {
+			// Fallback: use raw stdout.
+			result.Response = raw
+		}
+
+		handle.mu.Lock()
+		handle.result = &result
+		handle.proc = nil
+		handle.mu.Unlock()
+
+		if cfg.OnComplete != nil {
+			cfg.OnComplete(result)
+		}
+	}()
+
+	if cfg.Blocking {
+		// Wait for completion and return result directly.
+		<-handle.done
+		handle.mu.Lock()
+		r := handle.result
+		handle.mu.Unlock()
+		return nil, r, nil
+	}
+
+	return handle, nil, nil
+}

internal/extensions/symbols.go

@@ -23,9 +23,31 @@ func Symbols() interp.Exports {
 			"API":            reflect.ValueOf((*API)(nil)),
 			"Context":        reflect.ValueOf((*Context)(nil)),
 			"ToolDef":        reflect.ValueOf((*ToolDef)(nil)),
+			"ToolContext":    reflect.ValueOf((*ToolContext)(nil)),
+			"ShortcutDef":    reflect.ValueOf((*ShortcutDef)(nil)),
 			"CommandDef":     reflect.ValueOf((*CommandDef)(nil)),
 			"PrintBlockOpts": reflect.ValueOf((*PrintBlockOpts)(nil)),
 
+			// Session types
+			"SessionMessage": reflect.ValueOf((*SessionMessage)(nil)),
+			"ExtensionEntry": reflect.ValueOf((*ExtensionEntry)(nil)),
+
+			// Option types
+			"OptionDef": reflect.ValueOf((*OptionDef)(nil)),
+
+			// Model info types
+			"ModelInfoEntry": reflect.ValueOf((*ModelInfoEntry)(nil)),
+
+			// Tool info types
+			"ToolInfo": reflect.ValueOf((*ToolInfo)(nil)),
+
+			// LLM completion types
+			"CompleteRequest":  reflect.ValueOf((*CompleteRequest)(nil)),
+			"CompleteResponse": reflect.ValueOf((*CompleteResponse)(nil)),
+
+			// Status bar types
+			"StatusBarEntry": reflect.ValueOf((*StatusBarEntry)(nil)),
+
 			// Widget types
 			"WidgetConfig":    reflect.ValueOf((*WidgetConfig)(nil)),
 			"WidgetContent":   reflect.ValueOf((*WidgetContent)(nil)),
@@ -37,6 +59,12 @@ func Symbols() interp.Exports {
 			// Header/Footer types
 			"HeaderFooterConfig": reflect.ValueOf((*HeaderFooterConfig)(nil)),
 
+			// UI visibility
+			"UIVisibility": reflect.ValueOf((*UIVisibility)(nil)),
+
+			// Context stats
+			"ContextStats": reflect.ValueOf((*ContextStats)(nil)),
+
 			// Overlay types
 			"OverlayAnchor":       reflect.ValueOf((*OverlayAnchor)(nil)),
 			"OverlayCenter":       reflect.ValueOf(OverlayCenter),
@@ -49,6 +77,9 @@ func Symbols() interp.Exports {
 			// Tool renderer types
 			"ToolRenderConfig": reflect.ValueOf((*ToolRenderConfig)(nil)),
 
+			// Message renderer types
+			"MessageRendererConfig": reflect.ValueOf((*MessageRendererConfig)(nil)),
+
 			// Editor interceptor types
 			"EditorKeyActionType":  reflect.ValueOf((*EditorKeyActionType)(nil)),
 			"EditorKeyPassthrough": reflect.ValueOf(EditorKeyPassthrough),
@@ -59,18 +90,50 @@ func Symbols() interp.Exports {
 			"EditorConfig":         reflect.ValueOf((*EditorConfig)(nil)),
 
 			// Prompt types
-			"PromptSelectConfig":  reflect.ValueOf((*PromptSelectConfig)(nil)),
-			"PromptSelectResult":  reflect.ValueOf((*PromptSelectResult)(nil)),
-			"PromptConfirmConfig": reflect.ValueOf((*PromptConfirmConfig)(nil)),
-			"PromptConfirmResult": reflect.ValueOf((*PromptConfirmResult)(nil)),
-			"PromptInputConfig":   reflect.ValueOf((*PromptInputConfig)(nil)),
-			"PromptInputResult":   reflect.ValueOf((*PromptInputResult)(nil)),
+			"PromptSelectConfig":      reflect.ValueOf((*PromptSelectConfig)(nil)),
+			"PromptSelectResult":      reflect.ValueOf((*PromptSelectResult)(nil)),
+			"PromptConfirmConfig":     reflect.ValueOf((*PromptConfirmConfig)(nil)),
+			"PromptConfirmResult":     reflect.ValueOf((*PromptConfirmResult)(nil)),
+			"PromptInputConfig":       reflect.ValueOf((*PromptInputConfig)(nil)),
+			"PromptInputResult":       reflect.ValueOf((*PromptInputResult)(nil)),
+			"PromptMultiSelectConfig": reflect.ValueOf((*PromptMultiSelectConfig)(nil)),
+			"PromptMultiSelectResult": reflect.ValueOf((*PromptMultiSelectResult)(nil)),
+
+			// Context filtering types
+			"ContextMessage":       reflect.ValueOf((*ContextMessage)(nil)),
+			"ContextPrepareEvent":  reflect.ValueOf((*ContextPrepareEvent)(nil)),
+			"ContextPrepareResult": reflect.ValueOf((*ContextPrepareResult)(nil)),
+
+			// Session lifecycle types
+			"BeforeForkEvent":           reflect.ValueOf((*BeforeForkEvent)(nil)),
+			"BeforeForkResult":          reflect.ValueOf((*BeforeForkResult)(nil)),
+			"BeforeSessionSwitchEvent":  reflect.ValueOf((*BeforeSessionSwitchEvent)(nil)),
+			"BeforeSessionSwitchResult": reflect.ValueOf((*BeforeSessionSwitchResult)(nil)),
+			"BeforeCompactEvent":        reflect.ValueOf((*BeforeCompactEvent)(nil)),
+			"BeforeCompactResult":       reflect.ValueOf((*BeforeCompactResult)(nil)),
+
+			// Subagent types
+			"SubagentConfig": reflect.ValueOf((*SubagentConfig)(nil)),
+			"SubagentResult": reflect.ValueOf((*SubagentResult)(nil)),
+			"SubagentUsage":  reflect.ValueOf((*SubagentUsage)(nil)),
+			"SubagentHandle": reflect.ValueOf((*SubagentHandle)(nil)),
+			"SubagentEvent":  reflect.ValueOf((*SubagentEvent)(nil)),
+
+			// Subagent lifecycle events
+			"SubagentStartEvent": reflect.ValueOf((*SubagentStartEvent)(nil)),
+			"SubagentChunkEvent": reflect.ValueOf((*SubagentChunkEvent)(nil)),
+			"SubagentEndEvent":   reflect.ValueOf((*SubagentEndEvent)(nil)),
+
+			// Theme types
+			"ThemeColor":       reflect.ValueOf((*ThemeColor)(nil)),
+			"ThemeColorConfig": reflect.ValueOf((*ThemeColorConfig)(nil)),
 
 			// Event structs
 			"ToolCallEvent":           reflect.ValueOf((*ToolCallEvent)(nil)),
 			"ToolCallResult":          reflect.ValueOf((*ToolCallResult)(nil)),
 			"ToolExecutionStartEvent": reflect.ValueOf((*ToolExecutionStartEvent)(nil)),
 			"ToolExecutionEndEvent":   reflect.ValueOf((*ToolExecutionEndEvent)(nil)),
+			"ToolOutputEvent":         reflect.ValueOf((*ToolOutputEvent)(nil)),
 			"ToolResultEvent":         reflect.ValueOf((*ToolResultEvent)(nil)),
 			"ToolResultResult":        reflect.ValueOf((*ToolResultResult)(nil)),
 			"InputEvent":              reflect.ValueOf((*InputEvent)(nil)),
@@ -84,6 +147,7 @@ func Symbols() interp.Exports {
 			"MessageEndEvent":         reflect.ValueOf((*MessageEndEvent)(nil)),
 			"SessionStartEvent":       reflect.ValueOf((*SessionStartEvent)(nil)),
 			"SessionShutdownEvent":    reflect.ValueOf((*SessionShutdownEvent)(nil)),
+			"ModelChangeEvent":        reflect.ValueOf((*ModelChangeEvent)(nil)),
 		},
 	}
 }

internal/extensions/test_api.go

@@ -0,0 +1,193 @@
+package extensions
+
+// NewTestAPI creates an API object wired for testing.
+// This is used by the test harness to load extensions and verify behavior.
+// The registration functions wire handlers directly to the provided extension.
+func NewTestAPI(ext *LoadedExtension) API {
+	reg := func(event EventType, fn HandlerFunc) {
+		ext.Handlers[event] = append(ext.Handlers[event], fn)
+	}
+
+	return API{
+		onToolCall: func(h func(ToolCallEvent, Context) *ToolCallResult) {
+			reg(ToolCall, func(e Event, c Context) Result {
+				r := h(e.(ToolCallEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
+		onToolExecStart: func(h func(ToolExecutionStartEvent, Context)) {
+			reg(ToolExecutionStart, func(e Event, c Context) Result {
+				h(e.(ToolExecutionStartEvent), c)
+				return nil
+			})
+		},
+		onToolExecEnd: func(h func(ToolExecutionEndEvent, Context)) {
+			reg(ToolExecutionEnd, func(e Event, c Context) Result {
+				h(e.(ToolExecutionEndEvent), c)
+				return nil
+			})
+		},
+		onToolOutput: func(h func(ToolOutputEvent, Context)) {
+			reg(ToolOutput, func(e Event, c Context) Result {
+				h(e.(ToolOutputEvent), c)
+				return nil
+			})
+		},
+		onToolResult: func(h func(ToolResultEvent, Context) *ToolResultResult) {
+			reg(ToolResult, func(e Event, c Context) Result {
+				r := h(e.(ToolResultEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
+		onInput: func(h func(InputEvent, Context) *InputResult) {
+			reg(Input, func(e Event, c Context) Result {
+				r := h(e.(InputEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
+		onBeforeAgentStart: func(h func(BeforeAgentStartEvent, Context) *BeforeAgentStartResult) {
+			reg(BeforeAgentStart, func(e Event, c Context) Result {
+				r := h(e.(BeforeAgentStartEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
+		onAgentStart: func(h func(AgentStartEvent, Context)) {
+			reg(AgentStart, func(e Event, c Context) Result {
+				h(e.(AgentStartEvent), c)
+				return nil
+			})
+		},
+		onAgentEnd: func(h func(AgentEndEvent, Context)) {
+			reg(AgentEnd, func(e Event, c Context) Result {
+				h(e.(AgentEndEvent), c)
+				return nil
+			})
+		},
+		onMessageStart: func(h func(MessageStartEvent, Context)) {
+			reg(MessageStart, func(e Event, c Context) Result {
+				h(e.(MessageStartEvent), c)
+				return nil
+			})
+		},
+		onMessageUpdate: func(h func(MessageUpdateEvent, Context)) {
+			reg(MessageUpdate, func(e Event, c Context) Result {
+				h(e.(MessageUpdateEvent), c)
+				return nil
+			})
+		},
+		onMessageEnd: func(h func(MessageEndEvent, Context)) {
+			reg(MessageEnd, func(e Event, c Context) Result {
+				h(e.(MessageEndEvent), c)
+				return nil
+			})
+		},
+		onSessionStart: func(h func(SessionStartEvent, Context)) {
+			reg(SessionStart, func(e Event, c Context) Result {
+				h(e.(SessionStartEvent), c)
+				return nil
+			})
+		},
+		onSessionShutdown: func(h func(SessionShutdownEvent, Context)) {
+			reg(SessionShutdown, func(e Event, c Context) Result {
+				h(e.(SessionShutdownEvent), c)
+				return nil
+			})
+		},
+		onModelChange: func(h func(ModelChangeEvent, Context)) {
+			reg(ModelChange, func(e Event, c Context) Result {
+				h(e.(ModelChangeEvent), c)
+				return nil
+			})
+		},
+		onContextPrepare: func(h func(ContextPrepareEvent, Context) *ContextPrepareResult) {
+			reg(ContextPrepare, func(e Event, c Context) Result {
+				r := h(e.(ContextPrepareEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
+		onBeforeFork: func(h func(BeforeForkEvent, Context) *BeforeForkResult) {
+			reg(BeforeFork, func(e Event, c Context) Result {
+				r := h(e.(BeforeForkEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
+		onBeforeSessionSwitch: func(h func(BeforeSessionSwitchEvent, Context) *BeforeSessionSwitchResult) {
+			reg(BeforeSessionSwitch, func(e Event, c Context) Result {
+				r := h(e.(BeforeSessionSwitchEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
+		onBeforeCompact: func(h func(BeforeCompactEvent, Context) *BeforeCompactResult) {
+			reg(BeforeCompact, func(e Event, c Context) Result {
+				r := h(e.(BeforeCompactEvent), c)
+				if r == nil {
+					return nil
+				}
+				return *r
+			})
+		},
+		registerToolFn: func(tool ToolDef) {
+			ext.Tools = append(ext.Tools, tool)
+		},
+		registerCmdFn: func(cmd CommandDef) {
+			ext.Commands = append(ext.Commands, cmd)
+		},
+		registerToolRendererFn: func(config ToolRenderConfig) {
+			ext.ToolRenderers = append(ext.ToolRenderers, config)
+		},
+		onCustomEvent: func(name string, handler func(string)) {
+			if ext.CustomEventHandlers == nil {
+				ext.CustomEventHandlers = make(map[string][]func(string))
+			}
+			ext.CustomEventHandlers[name] = append(ext.CustomEventHandlers[name], handler)
+		},
+		registerOption: func(opt OptionDef) {
+			ext.Options = append(ext.Options, opt)
+		},
+		registerShortcutFn: func(def ShortcutDef, handler func(Context)) {
+			ext.Shortcuts = append(ext.Shortcuts, ShortcutEntry{Def: def, Handler: handler})
+		},
+		registerMessageRendererFn: func(config MessageRendererConfig) {
+			ext.MessageRenderers = append(ext.MessageRenderers, config)
+		},
+		onSubagentStart: func(h func(SubagentStartEvent, Context)) {
+			reg(SubagentStart, func(e Event, c Context) Result {
+				h(e.(SubagentStartEvent), c)
+				return nil
+			})
+		},
+		onSubagentChunk: func(h func(SubagentChunkEvent, Context)) {
+			reg(SubagentChunk, func(e Event, c Context) Result {
+				h(e.(SubagentChunkEvent), c)
+				return nil
+			})
+		},
+		onSubagentEnd: func(h func(SubagentEndEvent, Context)) {
+			reg(SubagentEnd, func(e Event, c Context) Result {
+				h(e.(SubagentEndEvent), c)
+				return nil
+			})
+		},
+	}
+}

internal/extensions/wrapper.go

@@ -2,6 +2,7 @@ package extensions
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 
 	"charm.land/fantasy"
@@ -9,19 +10,17 @@ import (
 
 // WrapToolsWithExtensions wraps each tool so that ToolCall and ToolResult
 // events are emitted through the extension runner before and after execution.
-// This is the Go equivalent of Pi's wrapper.ts pattern.
-//
+
 // If the runner has no relevant handlers the original tools are returned
 // unchanged (zero overhead).
 func WrapToolsWithExtensions(tools []fantasy.AgentTool, runner *Runner) []fantasy.AgentTool {
 	if runner == nil {
 		return tools
 	}
-	if !runner.HasHandlers(ToolCall) && !runner.HasHandlers(ToolResult) &&
-		!runner.HasHandlers(ToolExecutionStart) && !runner.HasHandlers(ToolExecutionEnd) {
-		return tools
-	}
-
+	// Always wrap tools through the runner so that SetActiveTools
+	// (disabled-tool checking) and event handlers both work. The
+	// overhead for disabled-tool checking is a single map lookup
+	// per tool call, which is negligible.
 	wrapped := make([]fantasy.AgentTool, len(tools))
 	for i, tool := range tools {
 		wrapped[i] = &wrappedTool{inner: tool, runner: runner}
@@ -31,14 +30,47 @@ func WrapToolsWithExtensions(tools []fantasy.AgentTool, runner *Runner) []fantas
 
 // ExtensionToolsAsFantasy converts ToolDef values registered by extensions
 // into fantasy.AgentTool implementations so the LLM can invoke them.
-func ExtensionToolsAsFantasy(defs []ToolDef) []fantasy.AgentTool {
+// The runner is optional; if provided, ToolContext.OnProgress routes
+// progress messages through the runner's Print function.
+func ExtensionToolsAsFantasy(defs []ToolDef, runner *Runner) []fantasy.AgentTool {
 	tools := make([]fantasy.AgentTool, 0, len(defs))
 	for _, def := range defs {
-		tools = append(tools, &extensionTool{def: def})
+		tools = append(tools, &extensionTool{def: def, runner: runner})
 	}
 	return tools
 }
 
+// coreToolKinds maps built-in tool names to their kind classification.
+var coreToolKinds = map[string]string{
+	"bash":           "execute",
+	"edit":           "edit",
+	"write":          "edit",
+	"read":           "read",
+	"ls":             "read",
+	"grep":           "search",
+	"find":           "search",
+	"spawn_subagent": "agent",
+}
+
+// toolKindFor returns the ToolKind for a given tool name, defaulting to
+// "execute" for unknown tools (including MCP tools).
+func toolKindFor(toolName string) string {
+	if kind, ok := coreToolKinds[toolName]; ok {
+		return kind
+	}
+	return "execute"
+}
+
+// parseToolArgsJSON attempts to parse JSON-encoded tool args into a map.
+// Returns nil on failure (non-fatal convenience parsing).
+func parseToolArgsJSON(input string) map[string]any {
+	var parsed map[string]any
+	if json.Unmarshal([]byte(input), &parsed) == nil {
+		return parsed
+	}
+	return nil
+}
+
 // ---------------------------------------------------------------------------
 // wrappedTool — intercepts tool calls through the extension runner
 // ---------------------------------------------------------------------------
@@ -55,12 +87,24 @@ func (w *wrappedTool) SetProviderOptions(o fantasy.ProviderOptions) { w.inner.Se
 func (w *wrappedTool) Run(ctx context.Context, call fantasy.ToolCall) (fantasy.ToolResponse, error) {
 	toolName := w.inner.Info().Name
 
+	// 0. Check if tool is disabled via SetActiveTools.
+	if w.runner.IsToolDisabled(toolName) {
+		return fantasy.NewTextErrorResponse(
+				fmt.Sprintf("Error: tool %q is currently disabled", toolName)),
+			fmt.Errorf("tool %q disabled by extension", toolName)
+	}
+
+	kind := toolKindFor(toolName)
+
 	// 1. Emit ToolCall — extensions can block execution.
 	if w.runner.HasHandlers(ToolCall) {
 		result, _ := w.runner.Emit(ToolCallEvent{
 			ToolName:   toolName,
 			ToolCallID: call.ID,
+			ToolKind:   kind,
 			Input:      call.Input,
+			ParsedArgs: parseToolArgsJSON(call.Input),
+			Source:     "llm",
 		})
 		if r, ok := result.(ToolCallResult); ok && r.Block {
 			reason := r.Reason
@@ -74,7 +118,7 @@ func (w *wrappedTool) Run(ctx context.Context, call fantasy.ToolCall) (fantasy.T
 
 	// 2. Emit ToolExecutionStart.
 	if w.runner.HasHandlers(ToolExecutionStart) {
-		_, _ = w.runner.Emit(ToolExecutionStartEvent{ToolName: toolName})
+		_, _ = w.runner.Emit(ToolExecutionStartEvent{ToolCallID: call.ID, ToolName: toolName, ToolKind: kind})
 	}
 
 	// 3. Execute the actual tool.
@@ -82,16 +126,19 @@ func (w *wrappedTool) Run(ctx context.Context, call fantasy.ToolCall) (fantasy.T
 
 	// 4. Emit ToolExecutionEnd.
 	if w.runner.HasHandlers(ToolExecutionEnd) {
-		_, _ = w.runner.Emit(ToolExecutionEndEvent{ToolName: toolName})
+		_, _ = w.runner.Emit(ToolExecutionEndEvent{ToolCallID: call.ID, ToolName: toolName, ToolKind: kind})
 	}
 
 	// 5. Emit ToolResult — extensions can modify output.
 	if w.runner.HasHandlers(ToolResult) {
 		result, _ := w.runner.Emit(ToolResultEvent{
-			ToolName: toolName,
-			Input:    call.Input,
-			Content:  resp.Content,
-			IsError:  err != nil || resp.IsError,
+			ToolCallID: call.ID,
+			ToolName:   toolName,
+			ToolKind:   kind,
+			Input:      call.Input,
+			Content:    resp.Content,
+			IsError:    err != nil || resp.IsError,
+			Metadata:   resp.Metadata,
 		})
 		if r, ok := result.(ToolResultResult); ok {
 			if r.Content != nil {
@@ -112,21 +159,84 @@ func (w *wrappedTool) Run(ctx context.Context, call fantasy.ToolCall) (fantasy.T
 
 type extensionTool struct {
 	def             ToolDef
+	runner          *Runner // optional; enables ToolContext.OnProgress
 	providerOptions fantasy.ProviderOptions
 }
 
 func (t *extensionTool) Info() fantasy.ToolInfo {
-	return fantasy.ToolInfo{
+	info := fantasy.ToolInfo{
 		Name:        t.def.Name,
 		Description: t.def.Description,
 	}
+
+	// Parse the extension's JSON Schema and extract the properties map.
+	// Fantasy expects Parameters to contain property definitions directly
+	// (e.g. {"command": {"type":"string"}}) and wraps them into a full
+	// JSON Schema object internally. If the extension provides a full
+	// schema with "type":"object" and "properties", we extract just the
+	// properties. Required fields are also extracted if present.
+	if t.def.Parameters != "" {
+		var schema map[string]any
+		if err := json.Unmarshal([]byte(t.def.Parameters), &schema); err == nil {
+			if props, ok := schema["properties"].(map[string]any); ok {
+				info.Parameters = props
+			} else {
+				// Schema doesn't have "properties" — use as-is (may be
+				// a flat property map already matching fantasy's format).
+				info.Parameters = schema
+			}
+			// Extract required fields if present.
+			if req, ok := schema["required"].([]any); ok {
+				for _, r := range req {
+					if s, ok := r.(string); ok {
+						info.Required = append(info.Required, s)
+					}
+				}
+			}
+		}
+	}
+
+	// Ensure Parameters and Required are never nil — the OpenAI Responses API
+	// rejects tools where these fields serialize to JSON null instead of
+	// empty object/array.
+	if info.Parameters == nil {
+		info.Parameters = map[string]any{}
+	}
+	if info.Required == nil {
+		info.Required = []string{}
+	}
+
+	return info
 }
 
 func (t *extensionTool) ProviderOptions() fantasy.ProviderOptions     { return t.providerOptions }
 func (t *extensionTool) SetProviderOptions(o fantasy.ProviderOptions) { t.providerOptions = o }
 
-func (t *extensionTool) Run(_ context.Context, call fantasy.ToolCall) (fantasy.ToolResponse, error) {
-	result, err := t.def.Execute(call.Input)
+func (t *extensionTool) Run(ctx context.Context, call fantasy.ToolCall) (fantasy.ToolResponse, error) {
+	var result string
+	var err error
+
+	if t.def.ExecuteWithContext != nil {
+		tc := ToolContext{
+			IsCancelled: func() bool {
+				return ctx.Err() != nil
+			},
+			OnProgress: func(text string) {
+				if t.runner != nil {
+					t.runner.mu.RLock()
+					printFn := t.runner.ctx.Print
+					t.runner.mu.RUnlock()
+					if printFn != nil {
+						printFn(text)
+					}
+				}
+			},
+		}
+		result, err = t.def.ExecuteWithContext(call.Input, tc)
+	} else {
+		result, err = t.def.Execute(call.Input)
+	}
+
 	if err != nil {
 		return fantasy.NewTextErrorResponse(err.Error()), err
 	}

internal/extensions/wrapper_test.go

@@ -48,8 +48,13 @@ func TestWrapToolsWithExtensions_NoRelevantHandlers(t *testing.T) {
 	}))
 	tools := []fantasy.AgentTool{newMockTool("test")}
 	result := WrapToolsWithExtensions(tools, r)
-	if result[0] != tools[0] {
-		t.Error("expected original tool when no tool handlers exist")
+	// Tools are always wrapped now (for SetActiveTools support),
+	// but Info() should pass through correctly.
+	if result[0] == tools[0] {
+		t.Error("expected wrapped tool (always wraps for SetActiveTools)")
+	}
+	if result[0].Info().Name != "test" {
+		t.Errorf("expected name 'test', got %q", result[0].Info().Name)
 	}
 }
 
@@ -102,6 +107,22 @@ func TestWrappedTool_NormalExecution(t *testing.T) {
 	}
 }
 
+func TestWrappedTool_SourceField(t *testing.T) {
+	var gotSource string
+	r := makeRunner(makeHandlerExt("source.go", map[EventType][]HandlerFunc{
+		ToolCall: {func(e Event, c Context) Result {
+			gotSource = e.(ToolCallEvent).Source
+			return nil
+		}},
+	}))
+
+	tools := WrapToolsWithExtensions([]fantasy.AgentTool{newMockTool("bash")}, r)
+	_, _ = tools[0].Run(context.Background(), fantasy.ToolCall{ID: "1", Input: "{}"})
+	if gotSource != "llm" {
+		t.Errorf("expected Source='llm', got %q", gotSource)
+	}
+}
+
 func TestWrappedTool_BlockExecution(t *testing.T) {
 	var toolRan bool
 	r := makeRunner(makeHandlerExt("blocker.go", map[EventType][]HandlerFunc{
@@ -181,7 +202,7 @@ func TestExtensionToolsAsFantasy(t *testing.T) {
 		},
 	}
 
-	tools := ExtensionToolsAsFantasy(defs)
+	tools := ExtensionToolsAsFantasy(defs, nil)
 	if len(tools) != 1 {
 		t.Fatalf("expected 1 tool, got %d", len(tools))
 	}
@@ -211,7 +232,7 @@ func TestExtensionTool_Error(t *testing.T) {
 		},
 	}
 
-	tools := ExtensionToolsAsFantasy(defs)
+	tools := ExtensionToolsAsFantasy(defs, nil)
 	resp, err := tools[0].Run(context.Background(), fantasy.ToolCall{Input: "x"})
 	if err == nil {
 		t.Error("expected error")
@@ -221,9 +242,104 @@ func TestExtensionTool_Error(t *testing.T) {
 	}
 }
 
+func TestExtensionTool_ExecuteWithContext(t *testing.T) {
+	var gotCancelled bool
+	var gotProgress []string
+
+	defs := []ToolDef{
+		{
+			Name: "rich",
+			ExecuteWithContext: func(input string, tc ToolContext) (string, error) {
+				gotCancelled = tc.IsCancelled()
+				tc.OnProgress("step 1")
+				tc.OnProgress("step 2")
+				return "done: " + input, nil
+			},
+		},
+	}
+
+	// Without runner, OnProgress is a no-op.
+	tools := ExtensionToolsAsFantasy(defs, nil)
+	resp, err := tools[0].Run(context.Background(), fantasy.ToolCall{Input: "test"})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if resp.Content != "done: test" {
+		t.Errorf("expected 'done: test', got %q", resp.Content)
+	}
+	if gotCancelled {
+		t.Error("expected IsCancelled=false for non-cancelled context")
+	}
+
+	// With runner, OnProgress routes through Print.
+	runner := NewRunner(nil)
+	runner.SetContext(Context{
+		Print: func(text string) { gotProgress = append(gotProgress, text) },
+	})
+	defs2 := []ToolDef{
+		{
+			Name: "rich2",
+			ExecuteWithContext: func(input string, tc ToolContext) (string, error) {
+				tc.OnProgress("hello")
+				return "ok", nil
+			},
+		},
+	}
+	tools2 := ExtensionToolsAsFantasy(defs2, runner)
+	_, err = tools2[0].Run(context.Background(), fantasy.ToolCall{Input: ""})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(gotProgress) != 1 || gotProgress[0] != "hello" {
+		t.Errorf("expected [hello], got %v", gotProgress)
+	}
+}
+
+func TestExtensionTool_ExecuteWithContextPriority(t *testing.T) {
+	// When both Execute and ExecuteWithContext are set, ExecuteWithContext wins.
+	defs := []ToolDef{
+		{
+			Name:    "both",
+			Execute: func(input string) (string, error) { return "simple", nil },
+			ExecuteWithContext: func(input string, tc ToolContext) (string, error) {
+				return "rich", nil
+			},
+		},
+	}
+	tools := ExtensionToolsAsFantasy(defs, nil)
+	resp, err := tools[0].Run(context.Background(), fantasy.ToolCall{Input: ""})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if resp.Content != "rich" {
+		t.Errorf("expected 'rich' (ExecuteWithContext), got %q", resp.Content)
+	}
+}
+
+func TestExtensionTool_CancelledContext(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // cancel immediately
+
+	var sawCancelled bool
+	defs := []ToolDef{
+		{
+			Name: "checkcancel",
+			ExecuteWithContext: func(input string, tc ToolContext) (string, error) {
+				sawCancelled = tc.IsCancelled()
+				return "ok", nil
+			},
+		},
+	}
+	tools := ExtensionToolsAsFantasy(defs, nil)
+	_, _ = tools[0].Run(ctx, fantasy.ToolCall{Input: ""})
+	if !sawCancelled {
+		t.Error("expected IsCancelled=true for cancelled context")
+	}
+}
+
 func TestExtensionTool_ProviderOptions(t *testing.T) {
 	defs := []ToolDef{{Name: "test", Execute: func(string) (string, error) { return "", nil }}}
-	tools := ExtensionToolsAsFantasy(defs)
+	tools := ExtensionToolsAsFantasy(defs, nil)
 
 	// Initially nil.
 	opts := tools[0].ProviderOptions()

internal/kitsetup/setup.go

@@ -79,6 +79,7 @@ func BuildProviderConfig() (*models.ProviderConfig, string, error) {
 		NumGPU:         &numGPU,
 		MainGPU:        &mainGPU,
 		TLSSkipVerify:  viper.GetBool("tls-skip-verify"),
+		ThinkingLevel:  models.ParseThinkingLevel(viper.GetString("thinking-level")),
 	}
 
 	return cfg, systemPrompt, nil
@@ -186,7 +187,7 @@ func loadExtensions() (*extensions.Runner, extensionCreationOpts, error) {
 		return extensions.WrapToolsWithExtensions(tools, runner)
 	}
 
-	extTools := extensions.ExtensionToolsAsFantasy(runner.RegisteredTools())
+	extTools := extensions.ExtensionToolsAsFantasy(runner.RegisteredTools(), runner)
 
 	return runner, extensionCreationOpts{
 		toolWrapper: wrapper,

internal/message/content.go

@@ -4,11 +4,38 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"strings"
 	"time"
 
 	"charm.land/fantasy"
 )
 
+// sanitizeToolCallID ensures the ID matches Anthropic's required pattern:
+// ^[a-zA-Z0-9_-]+$ (alphanumeric, underscores, and hyphens only).
+// Invalid characters are replaced with underscores.
+func sanitizeToolCallID(id string) string {
+	var sb strings.Builder
+	for _, r := range id {
+		switch {
+		case (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z'):
+			sb.WriteRune(r)
+		case r >= '0' && r <= '9':
+			sb.WriteRune(r)
+		case r == '_' || r == '-':
+			sb.WriteRune(r)
+		default:
+			// Replace invalid characters with underscore
+			sb.WriteByte('_')
+		}
+	}
+	result := sb.String()
+	// Ensure non-empty (Anthropic requires at least one character)
+	if result == "" {
+		return "tool_0"
+	}
+	return result
+}
+
 // ContentPart is the marker interface for all message content block types.
 // A message contains a heterogeneous slice of ContentPart values, enabling
 // rich structured messages that carry text, reasoning, tool calls, tool
@@ -58,6 +85,16 @@ type ToolResult struct {
 
 func (ToolResult) isPart() {}
 
+// ImageContent holds image data within a message. The data is stored as raw
+// bytes (not base64-encoded); serialization handles encoding. MediaType is a
+// MIME type such as "image/png" or "image/jpeg".
+type ImageContent struct {
+	Data      []byte `json:"data"`
+	MediaType string `json:"media_type"`
+}
+
+func (ImageContent) isPart() {}
+
 // Finish marks the end of an assistant turn, carrying the stop reason.
 type Finish struct {
 	Reason string `json:"reason"` // "end_turn", "tool_use", "max_tokens", etc.
@@ -129,6 +166,17 @@ func (m *Message) ToolResults() []ToolResult {
 	return results
 }
 
+// Images returns all ImageContent parts from this message.
+func (m *Message) Images() []ImageContent {
+	var images []ImageContent
+	for _, part := range m.Parts {
+		if ic, ok := part.(ImageContent); ok {
+			images = append(images, ic)
+		}
+	}
+	return images
+}
+
 // Reasoning returns the ReasoningContent if present, or a zero value.
 func (m *Message) Reasoning() ReasoningContent {
 	for _, part := range m.Parts {
@@ -170,6 +218,7 @@ const (
 	toolCallType   partType = "tool_call"
 	toolResultType partType = "tool_result"
 	finishType     partType = "finish"
+	imageType      partType = "image"
 )
 
 type partWrapper struct {
@@ -194,6 +243,8 @@ func MarshalParts(parts []ContentPart) ([]byte, error) {
 			pt = toolResultType
 		case Finish:
 			pt = finishType
+		case ImageContent:
+			pt = imageType
 		default:
 			return nil, fmt.Errorf("unknown content part type: %T", part)
 		}
@@ -247,6 +298,12 @@ func UnmarshalParts(data []byte) ([]ContentPart, error) {
 				return nil, fmt.Errorf("failed to unmarshal finish part: %w", err)
 			}
 			part = p
+		case imageType:
+			var p ImageContent
+			if err := json.Unmarshal(w.Data, &p); err != nil {
+				return nil, fmt.Errorf("failed to unmarshal image part: %w", err)
+			}
+			part = p
 		default:
 			return nil, fmt.Errorf("unknown part type: %s", w.Type)
 		}
@@ -282,7 +339,7 @@ func (m *Message) ToFantasyMessages() []fantasy.Message {
 		// Add tool calls
 		for _, tc := range m.ToolCalls() {
 			parts = append(parts, fantasy.ToolCallPart{
-				ToolCallID: tc.ID,
+				ToolCallID: sanitizeToolCallID(tc.ID),
 				ToolName:   tc.Name,
 				Input:      tc.Input,
 			})
@@ -310,7 +367,7 @@ func (m *Message) ToFantasyMessages() []fantasy.Message {
 				}
 			}
 			parts = append(parts, fantasy.ToolResultPart{
-				ToolCallID: result.ToolCallID,
+				ToolCallID: sanitizeToolCallID(result.ToolCallID),
 				Output:     output,
 			})
 		}
@@ -323,13 +380,25 @@ func (m *Message) ToFantasyMessages() []fantasy.Message {
 		}}
 
 	case RoleUser:
+		var parts []fantasy.MessagePart
 		text := m.Content()
-		if text == "" {
+		if text != "" {
+			parts = append(parts, fantasy.TextPart{Text: text})
+		}
+		for _, part := range m.Parts {
+			if ic, ok := part.(ImageContent); ok {
+				parts = append(parts, fantasy.FilePart{
+					Data:      ic.Data,
+					MediaType: ic.MediaType,
+				})
+			}
+		}
+		if len(parts) == 0 {
 			return nil
 		}
 		return []fantasy.Message{{
 			Role:    fantasy.MessageRoleUser,
-			Content: []fantasy.MessagePart{fantasy.TextPart{Text: text}},
+			Content: parts,
 		}}
 
 	case RoleSystem:
@@ -388,6 +457,13 @@ func FromFantasyMessage(msg fantasy.Message) Message {
 					Thinking: p.Text,
 				})
 			}
+		case fantasy.FilePart:
+			if len(p.Data) > 0 {
+				m.Parts = append(m.Parts, ImageContent{
+					Data:      p.Data,
+					MediaType: p.MediaType,
+				})
+			}
 		}
 	}