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co-mono/packages/coding-agent/DEVELOPMENT.md
Mario Zechner 4ec2708bb3 Update coding-agent DEVELOPMENT.md to reflect current codebase 
- Fix external dependency name (pi-agent-core -> pi-agent)
- Add missing files: hooks/, custom-tools/, skills.ts, github-copilot.ts
- Update components list with all 18 current components
- Add Key Abstractions sections for hooks, custom tools, skills
- Add 'Adding a New Hook Event' to development guide
- Move config.ts to correct location in directory tree
2025-12-17 22:41:17 +01:00

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# coding-agent Development Guide
This document describes the architecture and development workflow for the coding-agent package.
## Architecture Overview
The coding-agent is structured into distinct layers:
```
┌─────────────────────────────────────────────────────────────┐
│ CLI Layer │
│ cli.ts → main.ts → cli/args.ts, cli/file-processor.ts │
└─────────────────────────────────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────┐
│ Mode Layer │
│ modes/interactive/ modes/print-mode.ts modes/rpc/ │
└─────────────────────────────────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────┐
│ Core Layer │
│ core/agent-session.ts (central abstraction) │
│ core/session-manager.ts, core/model-config.ts, etc. │
└─────────────────────────────────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────┐
│ External Dependencies │
│ @mariozechner/pi-agent (Agent, tools) │
│ @mariozechner/pi-ai (models, providers) │
│ @mariozechner/pi-tui (TUI components) │
└─────────────────────────────────────────────────────────────┘
```
## Directory Structure
```
src/
├── cli.ts # CLI entry point (shebang, calls main)
├── main.ts # Main orchestration, argument handling, mode routing
├── index.ts # Public API exports
├── config.ts # APP_NAME, VERSION, paths (getAgentDir, etc.)
├── cli/ # CLI-specific utilities
│ ├── args.ts # parseArgs(), printHelp(), Args interface
│ ├── file-processor.ts # processFileArguments() for @file args
│ ├── list-models.ts # --list-models implementation
│ └── session-picker.ts # selectSession() TUI for --resume
├── core/ # Core business logic (mode-agnostic)
│ ├── index.ts # Core exports
│ ├── agent-session.ts # AgentSession class - THE central abstraction
│ ├── bash-executor.ts # executeBash() with streaming, abort
│ ├── compaction.ts # Context compaction logic
│ ├── export-html.ts # exportSession(), exportFromFile()
│ ├── messages.ts # BashExecutionMessage, messageTransformer
│ ├── model-config.ts # findModel(), getAvailableModels(), getApiKeyForModel()
│ ├── model-resolver.ts # resolveModelScope(), restoreModelFromSession()
│ ├── session-manager.ts # SessionManager class - JSONL persistence
│ ├── settings-manager.ts # SettingsManager class - user preferences
│ ├── skills.ts # loadSkills(), skill discovery from multiple locations
│ ├── slash-commands.ts # loadSlashCommands() from ~/.pi/agent/commands/
│ ├── system-prompt.ts # buildSystemPrompt(), loadProjectContextFiles()
│ │
│ ├── oauth/ # OAuth authentication
│ │ ├── index.ts # OAuth exports
│ │ ├── anthropic.ts # Anthropic OAuth (Claude Pro/Max)
│ │ ├── github-copilot.ts # GitHub Copilot OAuth
│ │ └── storage.ts # Token persistence
│ │
│ ├── hooks/ # Hook system for extending behavior
│ │ ├── index.ts # Hook exports
│ │ ├── types.ts # HookAPI, HookContext, event types
│ │ ├── loader.ts # loadHooks() from multiple locations
│ │ ├── runner.ts # runHook() event dispatch
│ │ └── tool-wrapper.ts # wrapToolsWithHooks() for tool_call events
│ │
│ ├── custom-tools/ # Custom tool loading system
│ │ ├── index.ts # Custom tool exports
│ │ ├── types.ts # CustomToolFactory, CustomToolDefinition
│ │ └── loader.ts # loadCustomTools() from multiple locations
│ │
│ └── tools/ # Built-in tool implementations
│ ├── index.ts # Tool exports, allTools, codingTools
│ ├── bash.ts # Bash command execution
│ ├── edit.ts # Surgical file editing
│ ├── find.ts # File search by glob
│ ├── grep.ts # Content search (regex/literal)
│ ├── ls.ts # Directory listing
│ ├── read.ts # File reading (text and images)
│ ├── write.ts # File writing
│ ├── path-utils.ts # Path resolution utilities
│ └── truncate.ts # Output truncation utilities
├── modes/ # Run mode implementations
│ ├── index.ts # Re-exports InteractiveMode, runPrintMode, runRpcMode, RpcClient
│ ├── print-mode.ts # Non-interactive: process messages, print output, exit
│ │
│ ├── rpc/ # RPC mode for programmatic control
│ │ ├── rpc-mode.ts # runRpcMode() - JSON stdin/stdout protocol
│ │ ├── rpc-types.ts # RpcCommand, RpcResponse, RpcSessionState types
│ │ └── rpc-client.ts # RpcClient class for spawning/controlling agent
│ │
│ └── interactive/ # Interactive TUI mode
│ ├── interactive-mode.ts # InteractiveMode class
│ │
│ ├── components/ # TUI components
│ │ ├── assistant-message.ts # Agent response rendering
│ │ ├── bash-execution.ts # Bash output display
│ │ ├── compaction.ts # Compaction status display
│ │ ├── custom-editor.ts # Multi-line input editor
│ │ ├── dynamic-border.ts # Adaptive border rendering
│ │ ├── footer.ts # Status bar / footer
│ │ ├── hook-input.ts # Hook input dialog
│ │ ├── hook-selector.ts # Hook selection UI
│ │ ├── model-selector.ts # Model picker
│ │ ├── oauth-selector.ts # OAuth provider picker
│ │ ├── queue-mode-selector.ts # Message queue mode picker
│ │ ├── session-selector.ts # Session browser for --resume
│ │ ├── show-images-selector.ts # Image display toggle
│ │ ├── theme-selector.ts # Theme picker
│ │ ├── thinking-selector.ts # Thinking level picker
│ │ ├── tool-execution.ts # Tool call/result rendering
│ │ ├── user-message-selector.ts # Message selector for /branch
│ │ └── user-message.ts # User message rendering
│ │
│ └── theme/
│ ├── theme.ts # Theme loading, getEditorTheme(), etc.
│ ├── dark.json
│ ├── light.json
│ └── theme-schema.json
└── utils/ # Generic utilities
├── changelog.ts # parseChangelog(), getNewEntries()
├── clipboard.ts # copyToClipboard()
├── fuzzy.ts # Fuzzy string matching
├── mime.ts # MIME type detection
├── shell.ts # getShellConfig()
└── tools-manager.ts # ensureTool() - download fd, etc.
```
## Key Abstractions
### AgentSession (core/agent-session.ts)
The central abstraction that wraps the low-level `Agent` with:
- Session persistence (via SessionManager)
- Settings persistence (via SettingsManager)
- Model cycling with scoped models
- Context compaction
- Bash command execution
- Message queuing
- Hook integration
- Custom tool loading
All three modes (interactive, print, rpc) use AgentSession.
### InteractiveMode (modes/interactive/interactive-mode.ts)
Handles TUI rendering and user interaction:
- Subscribes to AgentSession events
- Renders messages, tool executions, streaming
- Manages editor, selectors, key handlers
- Delegates all business logic to AgentSession
### RPC Mode (modes/rpc/)
Headless operation via JSON protocol over stdin/stdout:
- **rpc-mode.ts**: `runRpcMode()` function that listens for JSON commands on stdin and emits responses/events on stdout
- **rpc-types.ts**: Typed protocol definitions (`RpcCommand`, `RpcResponse`, `RpcSessionState`)
- **rpc-client.ts**: `RpcClient` class for spawning the agent as a subprocess and controlling it programmatically
The RPC mode exposes the full AgentSession API via JSON commands. See [docs/rpc.md](docs/rpc.md) for protocol documentation.
### SessionManager (core/session-manager.ts)
Handles session persistence:
- JSONL format for append-only writes
- Session file location management
- Message loading/saving
- Model/thinking level persistence
### SettingsManager (core/settings-manager.ts)
Handles user preferences:
- Default model/provider
- Theme selection
- Queue mode
- Thinking block visibility
- Compaction settings
- Hook/custom tool paths
### Hook System (core/hooks/)
Extensibility layer for intercepting agent behavior:
- **loader.ts**: Discovers and loads hooks from `~/.pi/agent/hooks/`, `.pi/hooks/`, and CLI
- **runner.ts**: Dispatches events to registered hooks
- **tool-wrapper.ts**: Wraps tools to emit `tool_call` and `tool_result` events
- **types.ts**: Event types (`session`, `tool_call`, `tool_result`, `message`, `error`)
See [docs/hooks.md](docs/hooks.md) for full documentation.
### Custom Tools (core/custom-tools/)
System for adding LLM-callable tools:
- **loader.ts**: Discovers and loads tools from `~/.pi/agent/tools/`, `.pi/tools/`, and CLI
- **types.ts**: `CustomToolFactory`, `CustomToolDefinition`, `CustomToolResult`
See [docs/custom-tools.md](docs/custom-tools.md) for full documentation.
### Skills (core/skills.ts)
On-demand capability packages:
- Discovers SKILL.md files from multiple locations
- Provides specialized workflows and instructions
- Loaded when task matches description
See [docs/skills.md](docs/skills.md) for full documentation.
## Development Workflow
### Running in Development
Start the watch build in the monorepo root to continuously rebuild all packages:
```bash
# Terminal 1: Watch build (from monorepo root)
npm run dev
```
Then run the CLI with tsx in a separate terminal:
```bash
# Terminal 2: Run CLI (from monorepo root)
npx tsx packages/coding-agent/src/cli.ts
# With arguments
npx tsx packages/coding-agent/src/cli.ts --help
npx tsx packages/coding-agent/src/cli.ts -p "Hello"
# RPC mode
npx tsx packages/coding-agent/src/cli.ts --mode rpc --no-session
```
The watch build ensures changes to dependent packages (`pi-agent`, `pi-ai`, `pi-tui`) are automatically rebuilt.
### Type Checking
```bash
# From monorepo root
npm run check
```
### Building
```bash
# Build all packages
npm run build
# Build standalone binary
cd packages/coding-agent
npm run build:binary
```
## Adding New Features
### Adding a New Slash Command
1. If it's a UI-only command (e.g., `/theme`), add handler in `interactive-mode.ts` `setupEditorSubmitHandler()`
2. If it needs session logic, add method to `AgentSession` and call from mode
### Adding a New Tool
1. Create tool in `core/tools/` following existing patterns
2. Export from `core/tools/index.ts`
3. Add to `allTools` and optionally `codingTools`
4. Add description to `toolDescriptions` in `core/system-prompt.ts`
### Adding a New Hook Event
1. Add event type to `HookEvent` union in `core/hooks/types.ts`
2. Add emission point in relevant code (AgentSession, tool wrapper, etc.)
3. Document in `docs/hooks.md`
### Adding a New RPC Command
1. Add command type to `RpcCommand` union in `rpc-types.ts`
2. Add response type to `RpcResponse` union in `rpc-types.ts`
3. Add handler case in `handleCommand()` switch in `rpc-mode.ts`
4. Add client method in `RpcClient` class in `rpc-client.ts`
5. Document in `docs/rpc.md`
### Adding a New Selector
1. Create component in `modes/interactive/components/`
2. Use `showSelector()` helper in `interactive-mode.ts`:
```typescript
private showMySelector(): void {
this.showSelector((done) => {
const selector = new MySelectorComponent(
// ... params
(result) => {
// Handle selection
done();
this.showStatus(`Selected: ${result}`);
},
() => {
done();
this.ui.requestRender();
},
);
return { component: selector, focus: selector.getSelectList() };
});
}
```
## Testing
The package uses E2E tests only (no unit tests by design). Tests are in `test/`:
```bash
# Run all tests
npm test
# Run specific test pattern
npm test -- --testNamePattern="RPC"
# Run RPC example interactively
npx tsx test/rpc-example.ts
```
## Code Style
- No `any` types unless absolutely necessary
- No inline dynamic imports
- Use `showStatus()` for dim status messages
- Use `showError()` / `showWarning()` for errors/warnings
- Keep InteractiveMode focused on UI, delegate logic to AgentSession
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