# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Development Tools

- Runtime: Bun 1.2.11
- TypeScript with strict configuration

## Common Development Tasks

### Available npm/bun scripts from package.json:

```bash
# Test
bun test

# Formatting
bun run format          # Format code with prettier
bun run format:check    # Check code formatting

# Type checking
bun run typecheck       # Run TypeScript type checker
```

## Architecture Overview

This is a GitHub Action that enables Claude to interact with GitHub PRs and issues. The action operates in two main phases:

### Phase 1: Preparation (`src/entrypoints/prepare.ts`)

1. **Authentication Setup**: Establishes GitHub token via OIDC or GitHub App
2. **Permission Validation**: Verifies actor has write permissions
3. **Trigger Detection**: Uses mode-specific logic to determine if Claude should respond
4. **Context Creation**: Prepares GitHub context and initial tracking comment

### Phase 2: Execution (`base-action/`)

The `base-action/` directory contains the core Claude Code execution logic, which serves a dual purpose:

- **Standalone Action**: Published separately as `@anthropic-ai/claude-code-base-action` for direct use
- **Inner Logic**: Used internally by this GitHub Action after preparation phase completes

Execution steps:

1. **MCP Server Setup**: Installs and configures GitHub MCP server for tool access
2. **Prompt Generation**: Creates context-rich prompts from GitHub data
3. **Claude Integration**: Executes via multiple providers (Anthropic API, AWS Bedrock, Google Vertex AI)
4. **Result Processing**: Updates comments and creates branches/PRs as needed

### Key Architectural Components

#### Mode System (`src/modes/`)

- **Tag Mode** (`tag/`): Responds to `@claude` mentions and issue assignments
- **Agent Mode** (`agent/`): Automated execution for workflow_dispatch and schedule events only
- Extensible registry pattern in `modes/registry.ts`

#### GitHub Integration (`src/github/`)

- **Context Parsing** (`context.ts`): Unified GitHub event handling
- **Data Fetching** (`data/fetcher.ts`): Retrieves PR/issue data via GraphQL/REST
- **Data Formatting** (`data/formatter.ts`): Converts GitHub data to Claude-readable format
- **Branch Operations** (`operations/branch.ts`): Handles branch creation and cleanup
- **Comment Management** (`operations/comments/`): Creates and updates tracking comments

#### MCP Server Integration (`src/mcp/`)

- **GitHub Actions Server** (`github-actions-server.ts`): Workflow and CI access
- **GitHub Comment Server** (`github-comment-server.ts`): Comment operations
- **GitHub File Operations** (`github-file-ops-server.ts`): File system access
- Auto-installation and configuration in `install-mcp-server.ts`

#### Authentication & Security (`src/github/`)

- **Token Management** (`token.ts`): OIDC token exchange and GitHub App authentication
- **Permission Validation** (`validation/permissions.ts`): Write access verification
- **Actor Validation** (`validation/actor.ts`): Human vs bot detection

### Project Structure

```
src/
├── entrypoints/           # Action entry points
│   ├── prepare.ts         # Main preparation logic
│   ├── update-comment-link.ts  # Post-execution comment updates
│   └── format-turns.ts    # Claude conversation formatting
├── github/               # GitHub integration layer
│   ├── api/              # REST/GraphQL clients
│   ├── data/             # Data fetching and formatting
│   ├── operations/       # Branch, comment, git operations
│   ├── validation/       # Permission and trigger validation
│   └── utils/            # Image downloading, sanitization
├── modes/                # Execution modes
│   ├── tag/              # @claude mention mode
│   ├── agent/            # Automation mode
│   └── registry.ts       # Mode selection logic
├── mcp/                  # MCP server implementations
├── prepare/              # Preparation orchestration
└── utils/                # Shared utilities
```

## Important Implementation Notes

### Authentication Flow

- Uses GitHub OIDC token exchange for secure authentication
- Supports custom GitHub Apps via `APP_ID` and `APP_PRIVATE_KEY`
- Falls back to official Claude GitHub App if no custom app provided

### MCP Server Architecture

- Each MCP server has specific GitHub API access patterns
- Servers are auto-installed in `~/.claude/mcp/github-{type}-server/`
- Configuration merged with user-provided MCP config via `mcp_config` input

### Mode System Design

- Modes implement `Mode` interface with `shouldTrigger()` and `prepare()` methods
- Registry validates mode compatibility with GitHub event types
- Agent mode only works with workflow_dispatch and schedule events

### Comment Threading

- Single tracking comment updated throughout execution
- Progress indicated via dynamic checkboxes
- Links to job runs and created branches/PRs
- Sticky comment option for consolidated PR comments

## Code Conventions

- Use Bun-specific TypeScript configuration with `moduleResolution: "bundler"`
- Strict TypeScript with `noUnusedLocals` and `noUnusedParameters` enabled
- Prefer explicit error handling with detailed error messages
- Use discriminated unions for GitHub context types
- Implement retry logic for GitHub API operations via `utils/retry.ts`