diff --git a/btca.config.jsonc b/btca.config.jsonc
index 73cf32cc..e63f35ab 100644
--- a/btca.config.jsonc
+++ b/btca.config.jsonc
@@ -63,9 +63,9 @@
       "type": "git",
       "name": "yaegi",
       "url": "https://github.com/traefik/yaegi",
-      "branch": "main"
+      "branch": "master"
     }
   ],
   "model": "claude-haiku-4-5",
   "provider": "opencode"
-}
\ No newline at end of file
+}
diff --git a/cmd/extensions.go b/cmd/extensions.go
index 9eab83a2..ec31e2b1 100644
--- a/cmd/extensions.go
+++ b/cmd/extensions.go
@@ -103,6 +103,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"os/exec"
 	"strings"
 	"time"
 
@@ -157,7 +158,7 @@ func Init(api ext.API) {
 	api.RegisterCommand(ext.CommandDef{
 		Name:        "echo",
 		Description: "Echo back the provided text",
-		Execute: func(args string) (string, error) {
+		Execute: func(args string, ctx ext.Context) (string, error) {
 			if args == "" {
 				return "Usage: /echo <text>", nil
 			}
@@ -165,6 +166,29 @@ func Init(api ext.API) {
 		},
 	})
 
+	// ── Background work with SendMessage ─────────────────────────────
+	// ctx.SendMessage injects a message into the conversation and
+	// triggers a new agent turn. Safe to call from goroutines.
+
+	api.RegisterCommand(ext.CommandDef{
+		Name:        "run",
+		Description: "Run a shell command in the background and feed the result to the agent",
+		Execute: func(args string, ctx ext.Context) (string, error) {
+			if args == "" {
+				return "Usage: /run <command>", nil
+			}
+			go func() {
+				out, err := exec.Command("sh", "-c", args).CombinedOutput()
+				if err != nil {
+					ctx.SendMessage(fmt.Sprintf("Background command %q failed: %v\n%s", args, err, out))
+					return
+				}
+				ctx.SendMessage(fmt.Sprintf("Background command %q finished:\n%s", args, out))
+			}()
+			return fmt.Sprintf("Running %q in background...", args), nil
+		},
+	})
+
 	// ── Custom tools ──────────────────────────────────────────────────
 	// Custom tools are added to the agent's tool list and can be
 	// called by the LLM. Parameters is a JSON Schema string.
diff --git a/cmd/root.go b/cmd/root.go
index d772e79c..f17a1972 100644
--- a/cmd/root.go
+++ b/cmd/root.go
@@ -379,7 +379,9 @@ func extensionCommandsForUI(runner *extensions.Runner) []ui.ExtensionCommand {
 		cmds = append(cmds, ui.ExtensionCommand{
 			Name:        name,
 			Description: d.Description,
-			Execute:     d.Execute,
+			Execute: func(args string) (string, error) {
+				return d.Execute(args, runner.GetContext())
+			},
 		})
 	}
 	return cmds
@@ -610,6 +612,7 @@ func runNormalMode(ctx context.Context) error {
 			PrintInfo:   func(text string) { appInstance.PrintFromExtension("info", text) },
 			PrintError:  func(text string) { appInstance.PrintFromExtension("error", text) },
 			PrintBlock:  appInstance.PrintBlockFromExtension,
+			SendMessage: func(text string) { appInstance.Run(text) },
 		})
 		if agentResult.ExtRunner.HasHandlers(extensions.SessionStart) {
 			_, _ = agentResult.ExtRunner.Emit(extensions.SessionStartEvent{})
diff --git a/internal/core/bash.go b/internal/core/bash.go
index e9237728..4f9776d3 100644
--- a/internal/core/bash.go
+++ b/internal/core/bash.go
@@ -76,9 +76,7 @@ func executeBash(ctx context.Context, call fantasy.ToolCall) (fantasy.ToolRespon
 	timeout := defaultBashTimeout
 	if args.Timeout > 0 {
 		timeout = time.Duration(args.Timeout) * time.Second
-		if timeout > maxBashTimeout {
-			timeout = maxBashTimeout
-		}
+		timeout = min(timeout, maxBashTimeout)
 	}
 
 	cmdCtx, cancel := context.WithTimeout(ctx, timeout)
diff --git a/internal/core/edit.go b/internal/core/edit.go
index fa1d16c3..f36bade1 100644
--- a/internal/core/edit.go
+++ b/internal/core/edit.go
@@ -173,10 +173,7 @@ func generateDiff(path, old, new string, changeIdx int) string {
 
 	// Show context around the change
 	contextLines := 3
-	start := lineNum - contextLines - 1
-	if start < 0 {
-		start = 0
-	}
+	start := max(lineNum-contextLines-1, 0)
 
 	var diff strings.Builder
 	diff.WriteString(fmt.Sprintf("--- %s\n+++ %s\n", path, path))
diff --git a/internal/extensions/api.go b/internal/extensions/api.go
index fb6683cf..ac0d2708 100644
--- a/internal/extensions/api.go
+++ b/internal/extensions/api.go
@@ -51,6 +51,18 @@ type Context struct {
 	//       Subtitle:    "my-extension",
 	//   })
 	PrintBlock func(PrintBlockOpts)
+
+	// SendMessage injects a message into the conversation and triggers a
+	// new agent turn. If the agent is currently busy the message is queued
+	// and processed after the current turn completes.
+	//
+	// This is safe to call from goroutines. Common pattern:
+	//
+	//   go func() {
+	//       out, _ := exec.Command("kit", "-p", task).Output()
+	//       ctx.SendMessage("Subagent result:\n" + string(out))
+	//   }()
+	SendMessage func(string)
 }
 
 // PrintBlockOpts configures a custom styled block for PrintBlock.
@@ -189,7 +201,7 @@ type ToolDef struct {
 type CommandDef struct {
 	Name        string
 	Description string
-	Execute     func(args string) (string, error)
+	Execute     func(args string, ctx Context) (string, error)
 }
 
 // ---------------------------------------------------------------------------
diff --git a/internal/extensions/events.go b/internal/extensions/events.go
index 5eac0b02..75190812 100644
--- a/internal/extensions/events.go
+++ b/internal/extensions/events.go
@@ -4,6 +4,8 @@
 // input transformation, and lifecycle observation — all without recompilation.
 package extensions
 
+import "slices"
+
 // EventType identifies a point in KIT's lifecycle where extensions can hook in.
 type EventType string
 
@@ -60,10 +62,5 @@ func AllEventTypes() []EventType {
 
 // IsValid returns true if the event type is a recognised lifecycle event.
 func (e EventType) IsValid() bool {
-	for _, valid := range AllEventTypes() {
-		if e == valid {
-			return true
-		}
-	}
-	return false
+	return slices.Contains(AllEventTypes(), e)
 }
diff --git a/internal/extensions/loader.go b/internal/extensions/loader.go
index 46ade83f..ed9a702c 100644
--- a/internal/extensions/loader.go
+++ b/internal/extensions/loader.go
@@ -176,7 +176,7 @@ func loadSingleExtension(path string) (*LoadedExtension, error) {
 
 	initFn, ok := initVal.Interface().(func(API))
 	if !ok {
-		return nil, fmt.Errorf("Init has wrong signature (want func(ext.API), got %T)", initVal.Interface())
+		return nil, fmt.Errorf("init has wrong signature (want func(ext.API), got %T)", initVal.Interface())
 	}
 
 	// Build the API object that wires typed registration methods back to
diff --git a/internal/extensions/loader_test.go b/internal/extensions/loader_test.go
index e20dacfd..7cd3f081 100644
--- a/internal/extensions/loader_test.go
+++ b/internal/extensions/loader_test.go
@@ -3,6 +3,7 @@ package extensions
 import (
 	"os"
 	"path/filepath"
+	"slices"
 	"testing"
 )
 
@@ -20,14 +21,7 @@ func TestDiscoverExtensionPaths_ExplicitFile(t *testing.T) {
 	}
 
 	abs, _ := filepath.Abs(f)
-	found := false
-	for _, p := range paths {
-		if p == abs {
-			found = true
-			break
-		}
-	}
-	if !found {
+	if !slices.Contains(paths, abs) {
 		t.Errorf("expected %q in discovered paths %v", abs, paths)
 	}
 }
@@ -41,14 +35,7 @@ func TestDiscoverExtensionPaths_ExplicitDir(t *testing.T) {
 
 	paths := discoverExtensionPaths([]string{dir})
 	abs, _ := filepath.Abs(f)
-	found := false
-	for _, p := range paths {
-		if p == abs {
-			found = true
-			break
-		}
-	}
-	if !found {
+	if !slices.Contains(paths, abs) {
 		t.Errorf("expected %q in discovered paths %v", abs, paths)
 	}
 }
@@ -66,14 +53,7 @@ func TestDiscoverExtensionPaths_SubdirMainGo(t *testing.T) {
 
 	paths := discoverExtensionPaths([]string{dir})
 	abs, _ := filepath.Abs(main)
-	found := false
-	for _, p := range paths {
-		if p == abs {
-			found = true
-			break
-		}
-	}
-	if !found {
+	if !slices.Contains(paths, abs) {
 		t.Errorf("expected %q in discovered paths %v", abs, paths)
 	}
 }
@@ -298,7 +278,7 @@ func Init(api ext.API) {
 	api.RegisterCommand(ext.CommandDef{
 		Name:        "hello",
 		Description: "says hello",
-		Execute: func(args string) (string, error) {
+		Execute: func(args string, ctx ext.Context) (string, error) {
 			return "hello " + args, nil
 		},
 	})
@@ -405,9 +385,9 @@ func Init(api ext.API) {
 func TestGlobalExtensionsDir_XDG(t *testing.T) {
 	// Save and restore XDG_CONFIG_HOME.
 	orig := os.Getenv("XDG_CONFIG_HOME")
-	defer os.Setenv("XDG_CONFIG_HOME", orig)
+	defer func() { _ = os.Setenv("XDG_CONFIG_HOME", orig) }()
 
-	os.Setenv("XDG_CONFIG_HOME", "/custom/config")
+	_ = os.Setenv("XDG_CONFIG_HOME", "/custom/config")
 	dir := globalExtensionsDir()
 	expected := "/custom/config/kit/extensions"
 	if dir != expected {
@@ -417,9 +397,9 @@ func TestGlobalExtensionsDir_XDG(t *testing.T) {
 
 func TestGlobalExtensionsDir_Default(t *testing.T) {
 	orig := os.Getenv("XDG_CONFIG_HOME")
-	defer os.Setenv("XDG_CONFIG_HOME", orig)
+	defer func() { _ = os.Setenv("XDG_CONFIG_HOME", orig) }()
 
-	os.Setenv("XDG_CONFIG_HOME", "")
+	_ = os.Setenv("XDG_CONFIG_HOME", "")
 	dir := globalExtensionsDir()
 	home, _ := os.UserHomeDir()
 	expected := filepath.Join(home, ".config", "kit", "extensions")
diff --git a/internal/extensions/runner.go b/internal/extensions/runner.go
index 8336d356..6541b892 100644
--- a/internal/extensions/runner.go
+++ b/internal/extensions/runner.go
@@ -115,6 +115,13 @@ 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
diff --git a/internal/session/store.go b/internal/session/store.go
index 310a8f40..8468a3a3 100644
--- a/internal/session/store.go
+++ b/internal/session/store.go
@@ -129,7 +129,7 @@ func extractSessionInfo(path string) (*SessionInfo, error) {
 	if err != nil {
 		return nil, err
 	}
-	defer f.Close()
+	defer func() { _ = f.Close() }()
 
 	info := &SessionInfo{
 		Path: path,
diff --git a/internal/session/tree_manager.go b/internal/session/tree_manager.go
index d07c751b..b40b3511 100644
--- a/internal/session/tree_manager.go
+++ b/internal/session/tree_manager.go
@@ -106,7 +106,7 @@ func CreateTreeSession(cwd string) (*TreeManager, error) {
 	tm.file = f
 
 	if err := tm.writeEntry(&header); err != nil {
-		f.Close()
+		_ = f.Close()
 		return nil, fmt.Errorf("failed to write session header: %w", err)
 	}
 
diff --git a/internal/ui/compact_renderer.go b/internal/ui/compact_renderer.go
index 15f3f119..580462a6 100644
--- a/internal/ui/compact_renderer.go
+++ b/internal/ui/compact_renderer.go
@@ -156,10 +156,7 @@ func (r *CompactRenderer) RenderToolMessage(toolName, toolArgs, toolResult strin
 	nameStr := lipgloss.NewStyle().Foreground(theme.Tool).Bold(true).Render(displayName)
 
 	// Format params
-	paramBudget := r.width - 10 - len(displayName)
-	if paramBudget < 20 {
-		paramBudget = 20
-	}
+	paramBudget := max(r.width-10-len(displayName), 20)
 	params := formatToolParams(toolArgs, paramBudget)
 
 	// Build header line
@@ -188,8 +185,7 @@ func (r *CompactRenderer) RenderToolMessage(toolName, toolArgs, toolResult strin
 	var lines []string
 	lines = append(lines, header)
 	if body != "" {
-		bodyLines := strings.Split(body, "\n")
-		for _, line := range bodyLines {
+		for line := range strings.SplitSeq(body, "\n") {
 			lines = append(lines, "  "+line)
 		}
 	}
@@ -514,25 +510,3 @@ func (r *CompactRenderer) formatBashOutput(result string) string {
 	// Trim any leading/trailing whitespace from the final result
 	return strings.TrimSpace(formattedResult.String())
 }
-
-// determineResultType determines the display type for tool results
-func (r *CompactRenderer) determineResultType(toolName, result string) string {
-	toolName = strings.ToLower(toolName)
-
-	switch {
-	case strings.Contains(toolName, "read"):
-		return "Text"
-	case strings.Contains(toolName, "write"):
-		return "Write"
-	case strings.Contains(toolName, "bash") || strings.Contains(toolName, "command") || strings.Contains(toolName, "shell") || toolName == "run_shell_cmd":
-		return "Bash"
-	case strings.Contains(toolName, "list") || strings.Contains(toolName, "ls"):
-		return "List"
-	case strings.Contains(toolName, "search") || strings.Contains(toolName, "grep"):
-		return "Search"
-	case strings.Contains(toolName, "fetch") || strings.Contains(toolName, "http"):
-		return "Fetch"
-	default:
-		return "Result"
-	}
-}
diff --git a/internal/ui/enhanced_styles.go b/internal/ui/enhanced_styles.go
index 525e0602..a78670dc 100644
--- a/internal/ui/enhanced_styles.go
+++ b/internal/ui/enhanced_styles.go
@@ -247,17 +247,11 @@ func ApplyGradient(text string, colorA, colorB color.Color) string {
 	}
 
 	const maxStops = 8
-	segmentSize := len(runes) / maxStops
-	if segmentSize < 1 {
-		segmentSize = 1
-	}
+	segmentSize := max(len(runes)/maxStops, 1)
 
 	var result strings.Builder
 	for i := 0; i < len(runes); i += segmentSize {
-		end := i + segmentSize
-		if end > len(runes) {
-			end = len(runes)
-		}
+		end := min(i+segmentSize, len(runes))
 
 		pos := float64(i) / float64(len(runes))
 		c := interpolateColor(colorA, colorB, pos)
diff --git a/internal/ui/messages.go b/internal/ui/messages.go
index 3c3e0443..e6e4822b 100644
--- a/internal/ui/messages.go
+++ b/internal/ui/messages.go
@@ -544,10 +544,7 @@ func (r *MessageRenderer) RenderToolMessage(toolName, toolArgs, toolResult strin
 	nameStr := lipgloss.NewStyle().Foreground(theme.Tool).Bold(true).Render(displayName)
 
 	// Format params with width budget for the header line
-	paramBudget := r.width - 10 - len(displayName)
-	if paramBudget < 20 {
-		paramBudget = 20
-	}
+	paramBudget := max(r.width-10-len(displayName), 20)
 	params := formatToolParams(toolArgs, paramBudget)
 
 	header := iconStr + " " + nameStr
diff --git a/internal/ui/model.go b/internal/ui/model.go
index 154f91e8..bb766839 100644
--- a/internal/ui/model.go
+++ b/internal/ui/model.go
@@ -916,11 +916,13 @@ func (m *AppModel) printHelpMessage() tea.Cmd {
 		"- `/quit`: Exit the application\n\n"
 
 	if len(m.extensionCommands) > 0 {
-		help += "**Extensions:**\n"
+		var extHelp strings.Builder
+		extHelp.WriteString("**Extensions:**\n")
 		for _, ec := range m.extensionCommands {
-			help += fmt.Sprintf("- `%s`: %s\n", ec.Name, ec.Description)
+			fmt.Fprintf(&extHelp, "- `%s`: %s\n", ec.Name, ec.Description)
 		}
-		help += "\n"
+		extHelp.WriteString("\n")
+		help += extHelp.String()
 	}
 
 	help += "**Keys:**\n" +
diff --git a/internal/ui/tool_renderers.go b/internal/ui/tool_renderers.go
index c40fa815..fd9e2601 100644
--- a/internal/ui/tool_renderers.go
+++ b/internal/ui/tool_renderers.go
@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
-	"path/filepath"
 	"regexp"
 	"strconv"
 	"strings"
@@ -154,11 +153,8 @@ func renderDiffBlock(before, after string, startLine int, width int) string {
 					inserts = append(inserts, h.Lines[i])
 					i++
 				}
-				maxPairs := len(deletes)
-				if len(inserts) > maxPairs {
-					maxPairs = len(inserts)
-				}
-				for j := 0; j < maxPairs; j++ {
+				maxPairs := max(len(deletes), len(inserts))
+				for j := range maxPairs {
 					sl := splitLine{}
 					if j < len(deletes) {
 						sl.beforeNum = beforeLine
@@ -200,10 +196,7 @@ func renderDiffBlock(before, after string, startLine int, width int) string {
 	// Layout calculations
 	const indent = "  "
 	availableWidth := width - len(indent)
-	panelWidth := (availableWidth - 3) / 2 // " │ " divider
-	if panelWidth < 20 {
-		panelWidth = 20
-	}
+	panelWidth := max((availableWidth-3)/2, 20) // " │ " divider
 
 	// Gutter width from max line number
 	maxLineNum := 1
@@ -215,14 +208,8 @@ func renderDiffBlock(before, after string, startLine int, width int) string {
 			maxLineNum = l.afterNum
 		}
 	}
-	gutterWidth := len(fmt.Sprintf("%d", maxLineNum))
-	if gutterWidth < 3 {
-		gutterWidth = 3
-	}
-	contentWidth := panelWidth - gutterWidth - 4 // gutter + " - " or " + "
-	if contentWidth < 10 {
-		contentWidth = 10
-	}
+	gutterWidth := max(len(fmt.Sprintf("%d", maxLineNum)), 3)
+	contentWidth := max(panelWidth-gutterWidth-4, 10) // gutter + " - " or " + "
 
 	theme := getTheme()
 
@@ -395,14 +382,8 @@ func renderCodeBlock(content, fileName string, width int) string {
 
 	// Layout
 	const codeIndent = "  "
-	gutterWidth := maxNumWidth + 2
-	if gutterWidth < 5 {
-		gutterWidth = 5
-	}
-	codeWidth := width - gutterWidth - len(codeIndent)
-	if codeWidth < 20 {
-		codeWidth = 20
-	}
+	gutterWidth := max(maxNumWidth+2, 5)
+	codeWidth := max(width-gutterWidth-len(codeIndent), 20)
 
 	theme := getTheme()
 	gutterStyle := lipgloss.NewStyle().Foreground(theme.Muted).Background(theme.GutterBg).PaddingRight(1)
@@ -483,10 +464,7 @@ func renderWriteBlock(content, fileName string, width int) string {
 	}
 
 	// Line number width
-	numDigits := len(fmt.Sprintf("%d", totalLines))
-	if numDigits < 3 {
-		numDigits = 3
-	}
+	numDigits := max(len(fmt.Sprintf("%d", totalLines)), 3)
 
 	// Syntax highlight
 	displayContent := strings.Join(lines, "\n")
@@ -496,10 +474,7 @@ func renderWriteBlock(content, fileName string, width int) string {
 	// Layout
 	const codeIndent = "  "
 	gutterWidth := numDigits + 2
-	codeWidth := width - gutterWidth - len(codeIndent)
-	if codeWidth < 20 {
-		codeWidth = 20
-	}
+	codeWidth := max(width-gutterWidth-len(codeIndent), 20)
 
 	theme := getTheme()
 	gutterStyle := lipgloss.NewStyle().Foreground(theme.Muted).Background(theme.GutterBg).PaddingRight(1)
@@ -666,12 +641,6 @@ func syntaxHighlight(source, fileName string) string {
 	return strings.TrimRight(result, "\n")
 }
 
-// fileExtension returns the file extension (with dot) for a path, used to
-// help chroma pick the right lexer.
-func fileExtension(path string) string {
-	return filepath.Ext(path)
-}
-
 // ---------------------------------------------------------------------------
 // Helpers
 // ---------------------------------------------------------------------------
diff --git a/internal/ui/tree_selector.go b/internal/ui/tree_selector.go
index b905d399..9d84cde4 100644
--- a/internal/ui/tree_selector.go
+++ b/internal/ui/tree_selector.go
@@ -241,10 +241,7 @@ func (ts *TreeSelectorComponent) View() tea.View {
 		if ts.cursor >= visH {
 			startIdx = ts.cursor - visH + 1
 		}
-		endIdx := startIdx + visH
-		if endIdx > len(ts.flatNodes) {
-			endIdx = len(ts.flatNodes)
-		}
+		endIdx := min(startIdx+visH, len(ts.flatNodes))
 
 		for i := startIdx; i < endIdx; i++ {
 			node := ts.flatNodes[i]
@@ -274,10 +271,7 @@ func (ts *TreeSelectorComponent) IsActive() bool {
 
 func (ts *TreeSelectorComponent) visibleHeight() int {
 	// Reserve lines for header(3) + search(1) + separator(1) + footer(2).
-	h := ts.height/2 - 7
-	if h < 5 {
-		h = 5
-	}
+	h := max(ts.height/2-7, 5)
 	return h
 }