kit/AGENTS.md

OpenSpec Instructions

These instructions are for AI assistants working in this project.

Always open @/openspec/AGENTS.md when the request:

• Mentions planning or proposals (words like proposal, spec, change, plan)
• Introduces new capabilities, breaking changes, architecture shifts, or big performance/security work
• Sounds ambiguous and you need the authoritative spec before coding

Use @/openspec/AGENTS.md to learn:

• How to create and apply change proposals
• Spec format and conventions
• Project structure and guidelines

Keep this managed block so 'openspec update' can refresh the instructions.

KIT Agent Guidelines

Build/Test Commands

• Build: go build -o output/kit ./cmd/kit
• Test all: go test -race ./...
• Test single: go test -race ./cmd -run TestScriptExecution
• Lint: go vet ./...
• Format: go fmt ./...

Code Style

• Imports: stdlib → third-party → local (blank lines between)
• Naming: camelCase (unexported), PascalCase (exported)
• Errors: Always check, wrap with fmt.Errorf("context: %w", err)
• Logging: Use github.com/charmbracelet/log structured logging
• Types: Prefer any over interface{}
• JSON: snake_case tags with omitempty where appropriate
• Context: First parameter for blocking operations

Architecture

• Multi-provider LLM support via llm.Provider interface
• MCP client-server for tool integration
• Builtin servers: bash, fetch, todo, fs
• Extension system (internal/extensions/): Yaegi-interpreted Go, 13 lifecycle events, custom tools/commands/widgets/overlays/editor interceptors
• TUI (internal/ui/): Bubble Tea v2 parent-child model (AppModel → InputComponent, StreamComponent, etc.)
• Decoupling pattern: cmd/root.go has converter functions (e.g. widgetProviderForUI()) that bridge internal/extensions/ types to internal/ui/ types — the UI never imports extensions directly

Key Patterns

Yaegi (Extension Interpreter) Gotchas

• No interfaces across boundary: All extension-facing API types must be concrete structs, never interfaces. Yaegi crashes on interface wrapper generation.
• Function field bug: Named function references assigned to struct fields return zero values across the interpreter boundary. Always use anonymous closure literals:

  // WRONG: ctx.SetEditor(ext.EditorConfig{HandleKey: myHandler})
  // RIGHT: ctx.SetEditor(ext.EditorConfig{HandleKey: func(k, t string) ext.EditorKeyAction { return myHandler(k, t) }})
  

• Symbol exports: Every new type exposed to extensions must be added to internal/extensions/symbols.go

BubbleTea Integration

• No prog.Send() from inside Update(): Calling prog.Send() synchronously within a BubbleTea Update() handler deadlocks the event loop. Use go appInstance.NotifyWidgetUpdate() (async goroutine) instead.
• Height measurement: distributeHeight() in model.go must measure using the same render path as View(). If an interceptor wraps rendering, measure with the wrapper too, or layout will mismatch.
• Channel-based prompts: Extension prompt calls (PromptSelect, etc.) block on a chan PromptResponse. Extension slash commands run in dedicated goroutines (not tea.Cmd) to avoid stalling BubbleTea's Cmd scheduler.

Extension State Management

• Thread-safe maps on Runner: Widget/header/footer/editor state lives on the Runner with sync.RWMutex, queried by UI via callbacks
• Context function fields: The Context struct uses function fields (Print func(string), SetWidget func(WidgetConfig)) wired by closures in cmd/root.go
• Package-level vars in extensions: Yaegi supports package-level variables captured in closures — this is how extensions maintain state across event callbacks

Unicode in Widget Text

• Widget content renders through lipgloss.Style.Render() which preserves ANSI escape codes
• Use rune-based width calculations (len([]rune(s))) not byte length (len(s)) when aligning box-drawing characters or multi-byte symbols

Testing

Interactive TUI Testing with tmux

Use tmux to test Kit interactively without blocking the agent:

tmux new-session -d -s kittest -x 120 -y 40 "output/kit -e examples/extensions/my-ext.go --no-session 2>kit_stderr.log"
sleep 3
tmux capture-pane -t kittest -p          # read screen
tmux send-keys -t kittest '/command' Enter  # send input
tmux kill-session -t kittest              # cleanup

Non-Interactive Kit (Subprocess Spawning)

Extensions can spawn Kit as a subprocess for sub-agent patterns:

kit --quiet --no-session --no-extensions --system-prompt /path/to/prompt.txt --model provider/model "question"

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)
• Never guess or manually search the filesystem for external projects
• Example: btca ask -r https://github.com/user/repo -q "How does X work?"
• See .agents/skills/btca-cli/SKILL.md for full btca usage