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+# Claude Code Action Architecture & Flow
+
+This document provides a comprehensive overview of how the Claude Code Action works, from token exchange through post-run cleanup.
+
+## Overview
+
+The Claude Code Action is a sophisticated GitHub automation platform that enables Claude to interact with GitHub repositories through secure token exchange, intelligent mode detection, and comprehensive GitHub API integration.
+
+## High-Level Architecture
+
+```mermaid
+graph TD
+    Start([GitHub Action Triggered]) --> Setup[Setup Environment<br/>- Install Bun<br/>- Install Dependencies]
+    
+    Setup --> ParseContext[Parse GitHub Context<br/>- Extract event data<br/>- Parse inputs]
+    
+    ParseContext --> ModeDetection{Mode Detection}
+    
+    ModeDetection -->|Has explicit prompt| AgentMode[AGENT MODE<br/>Direct automation]
+    ModeDetection -->|@claude mention/assignment/label| TagMode[TAG MODE<br/>Interactive response]
+    ModeDetection -->|No trigger| DefaultAgent[Default to Agent<br/>(won't trigger)]
+    
+    %% Token Exchange Branch
+    AgentMode --> TokenExchange[Token Exchange Process]
+    TagMode --> TokenExchange
+    TokenExchange --> TokenMethod{Token Method}
+    
+    TokenMethod -->|Custom token provided| UseCustom[Use Custom GitHub Token]
+    TokenMethod -->|No custom token| OIDC[Generate OIDC Token<br/>core.getIDToken()]
+    
+    OIDC --> Exchange[Exchange OIDC for App Token<br/>api.anthropic.com/api/github/github-app-token-exchange]
+    Exchange --> CreateOctokit[Create Authenticated Octokit Client<br/>REST + GraphQL]
+    UseCustom --> CreateOctokit
+    
+    %% Permission Checks
+    CreateOctokit --> PermCheck[Check Write Permissions<br/>Only for entity contexts]
+    PermCheck -->|No permissions| PermFail[❌ Exit: No write access]
+    PermCheck -->|Has permissions| TriggerCheck{Check Trigger Conditions}
+    
+    %% Trigger Validation
+    TriggerCheck -->|Agent Mode| AgentTrigger{Has explicit prompt?}
+    TriggerCheck -->|Tag Mode| TagTrigger{Contains @claude mention<br/>or assignment/label?}
+    
+    AgentTrigger -->|No prompt| NoTrigger[❌ Skip: No trigger found]
+    AgentTrigger -->|Has prompt| PrepareAgent[Prepare Agent Mode]
+    TagTrigger -->|No mention| NoTrigger
+    TagTrigger -->|Has mention| PrepareTag[Prepare Tag Mode]
+    
+    %% Mode-Specific Preparation
+    PrepareAgent --> AgentPrep[Agent Mode Preparation<br/>- Create prompt file<br/>- Setup MCP servers<br/>- No tracking comment]
+    PrepareTag --> TagPrep[Tag Mode Preparation<br/>- Create tracking comment<br/>- Setup branches<br/>- Fetch GitHub data<br/>- Setup MCP servers]
+    
+    %% Data Fetching (Tag Mode)
+    TagPrep --> DataFetch[Fetch GitHub Data<br/>GraphQL + REST API]
+    DataFetch --> FetchWhat{What to fetch?}
+    
+    FetchWhat -->|Pull Request| PRData[PR Data:<br/>- Comments & reviews<br/>- Changed files + SHAs<br/>- Commit history<br/>- Author info]
+    FetchWhat -->|Issue| IssueData[Issue Data:<br/>- Comments<br/>- Issue details<br/>- Author info]
+    
+    PRData --> ProcessImages[Process Images<br/>Download & convert to base64]
+    IssueData --> ProcessImages
+    ProcessImages --> SetupBranch[Setup Branch<br/>- Create Claude branch<br/>- Configure git auth]
+    
+    %% MCP Server Setup
+    AgentPrep --> MCPSetup[Setup MCP Servers]
+    SetupBranch --> MCPSetup
+    
+    MCPSetup --> MCPServers{MCP Servers}
+    MCPServers --> GitHubActions[GitHub Actions Server<br/>- Workflow data<br/>- CI results]
+    MCPServers --> GitHubComments[GitHub Comment Server<br/>- Comment operations]
+    MCPServers --> GitHubFiles[GitHub File Ops Server<br/>- File operations<br/>- Branch management]
+    MCPServers --> GitHubInline[GitHub Inline Comment Server<br/>- PR review comments]
+    
+    GitHubActions --> PromptGen[Generate Prompt]
+    GitHubComments --> PromptGen
+    GitHubFiles --> PromptGen
+    GitHubInline --> PromptGen
+    
+    %% Prompt Generation
+    PromptGen --> PromptType{Prompt Type}
+    PromptType -->|Agent Mode| AgentPrompt[Agent Prompt:<br/>- Direct user prompt<br/>- Minimal context]
+    PromptType -->|Tag Mode| TagPrompt[Tag Prompt:<br/>- Rich GitHub context<br/>- PR/Issue details<br/>- Changed files<br/>- Comments & reviews<br/>- Commit instructions]
+    
+    AgentPrompt --> ClaudeRun[Run Claude Code]
+    TagPrompt --> ClaudeRun
+    
+    %% Claude Execution
+    ClaudeRun --> ClaudeExec[Claude Code Execution<br/>base-action/src/index.ts]
+    ClaudeExec --> ClaudeArgs[Prepare Claude Args<br/>- Prompt file path<br/>- Custom claude_args<br/>- Output format: stream-json]
+    
+    ClaudeArgs --> ClaudeProvider{Provider}
+    ClaudeProvider -->|Default| AnthropicAPI[Anthropic API<br/>ANTHROPIC_API_KEY]
+    ClaudeProvider -->|Bedrock| AWSBedrock[AWS Bedrock<br/>OIDC + AWS credentials]
+    ClaudeProvider -->|Vertex| GCPVertex[GCP Vertex AI<br/>OIDC + GCP credentials]
+    
+    AnthropicAPI --> ClaudeProcess[Spawn Claude Process<br/>- Named pipe for input<br/>- Stream JSON output]
+    AWSBedrock --> ClaudeProcess
+    GCPVertex --> ClaudeProcess
+    
+    ClaudeProcess --> ClaudeTools[Claude Tool Usage<br/>- MCP tools<br/>- File operations<br/>- GitHub API calls<br/>- Bash commands]
+    
+    ClaudeTools --> ClaudeOutput[Claude Output Processing<br/>- Capture execution log<br/>- Parse JSON stream<br/>- Extract metrics]
+    
+    %% Post-Run Actions
+    ClaudeOutput --> PostRun{Post-Run Actions}
+    
+    PostRun -->|Success| Success[✅ Success Path]
+    PostRun -->|Failure| Failure[❌ Failure Path]
+    
+    Success --> UpdateComment[Update Tracking Comment<br/>- Job run link<br/>- Branch link<br/>- PR link (if created)<br/>- Execution metrics]
+    Failure --> UpdateComment
+    
+    UpdateComment --> BranchCleanup[Branch Cleanup<br/>- Check for changes<br/>- Delete empty branches<br/>- Keep branches with commits]
+    
+    BranchCleanup --> FormatReport[Format Execution Report<br/>- Parse conversation turns<br/>- Format tool usage<br/>- Add to GitHub step summary]
+    
+    FormatReport --> RevokeToken[Revoke App Token<br/>DELETE /installation/token]
+    
+    RevokeToken --> End([Action Complete])
+```
+
+## Key Components
+
+### 1. Token Exchange Process
+
+The action uses a secure OIDC token exchange system:
+
+1. **OIDC Token Generation**: `core.getIDToken("claude-code-github-action")`
+2. **Token Exchange**: POST to `https://api.anthropic.com/api/github/github-app-token-exchange`
+3. **Authentication**: Creates authenticated Octokit clients for GitHub API access
+
+**Security Benefits:**
+- Repository-scoped access
+- Time-limited tokens
+- Permission-limited (only configured GitHub App permissions)
+- Automatic token masking in logs
+
+### 2. Mode Detection
+
+The action automatically detects the appropriate execution mode:
+
+#### **Agent Mode**
+- **Trigger**: Explicit `prompt` input provided
+- **Use Case**: Direct automation, custom workflows
+- **Behavior**: Minimal context, direct execution
+- **Tracking**: No tracking comments
+
+#### **Tag Mode**  
+- **Trigger**: @claude mentions, issue assignments, or labels
+- **Use Case**: Interactive GitHub responses
+- **Behavior**: Rich context, comprehensive GitHub data
+- **Tracking**: Creates and updates tracking comments
+
+### 3. Data Fetching (Tag Mode)
+
+When in Tag Mode, the action fetches comprehensive GitHub context:
+
+#### **Pull Request Data:**
+- Comments and reviews (including inline comments)
+- Changed files with SHAs
+- Commit history and metadata
+- Author information
+- File diff data
+
+#### **Issue Data:**
+- Issue details and metadata  
+- All comments
+- Author information
+- Labels and assignments
+
+#### **Image Processing:**
+- Downloads images from GitHub
+- Converts to base64 for Claude
+- Maps original URLs to processed content
+
+### 4. MCP Server Integration
+
+The action sets up multiple MCP (Model Context Protocol) servers to provide Claude with GitHub capabilities:
+
+#### **GitHub Actions Server**
+- Access to workflow runs and CI data
+- Build status and test results
+- Artifact information
+
+#### **GitHub Comment Server**
+- Comment creation and updates
+- Issue and PR comment management
+
+#### **GitHub File Operations Server**
+- File reading and writing
+- Branch creation and management
+- Commit operations
+
+#### **GitHub Inline Comment Server**
+- PR review comment operations
+- Line-specific feedback
+
+### 5. Prompt Generation
+
+The action generates context-rich prompts based on the detected mode:
+
+#### **Agent Mode Prompts:**
+- Direct user prompt
+- Minimal GitHub context
+- Focused on specific task
+
+#### **Tag Mode Prompts:**
+- Comprehensive GitHub context
+- PR/Issue details and history
+- Changed files and diffs
+- Comment threads and reviews
+- Commit instructions and guidelines
+
+### 6. Claude Execution
+
+The action runs Claude Code through multiple provider options:
+
+#### **Provider Support:**
+- **Anthropic API** (default): Direct API access with API key
+- **AWS Bedrock**: OIDC authentication with AWS credentials
+- **GCP Vertex AI**: OIDC authentication with GCP credentials
+
+#### **Execution Process:**
+1. **Named Pipe Setup**: Creates pipe for prompt input
+2. **Process Spawning**: Spawns Claude Code process
+3. **Stream Processing**: Captures JSON stream output
+4. **Tool Integration**: Enables MCP tools and GitHub operations
+
+### 7. Post-Run Actions
+
+After Claude execution, the action performs comprehensive cleanup and reporting:
+
+#### **Comment Updates:**
+- Updates tracking comments with results
+- Adds job run links and execution metrics
+- Includes branch and PR links when created
+
+#### **Branch Management:**
+- Checks for actual changes in Claude branches
+- Deletes empty branches to avoid clutter
+- Preserves branches with meaningful commits
+
+#### **Report Generation:**
+- Parses execution logs and conversation turns
+- Formats tool usage and results
+- Adds formatted report to GitHub step summary
+
+#### **Security Cleanup:**
+- Revokes GitHub App installation token
+- Cleans up temporary files and processes
+
+## Security Considerations
+
+### **Access Control:**
+- Repository-scoped permissions only
+- Write access validation for actors
+- Bot user controls and allowlists
+
+### **Token Management:**
+- Short-lived installation tokens
+- Automatic token revocation after use
+- Secure OIDC-based exchange
+
+### **Permission Boundaries:**
+- Limited to configured GitHub App permissions
+- No cross-repository access
+- Scoped to specific repository operations
+
+## Integration Points
+
+### **With Pullfrog:**
+The Claude Code Action can be integrated with Pullfrog's workflow system, providing:
+- Standardized agent interaction patterns
+- Consistent GitHub integration
+- Reusable authentication flows
+- Common MCP server infrastructure
+
+### **With GitHub:**
+- Native GitHub Actions integration
+- Comprehensive API coverage (REST + GraphQL)
+- Proper webhook handling
+- Standard GitHub UI integration
+
+## Development Notes
+
+### **Key Files:**
+- `src/entrypoints/prepare.ts`: Main preparation logic
+- `src/modes/`: Mode detection and handling
+- `src/github/token.ts`: OIDC token exchange
+- `src/mcp/`: MCP server implementations
+- `base-action/`: Core Claude Code execution
+
+### **Testing:**
+- Unit tests for individual components
+- Integration tests for full workflows
+- Local testing with `act` tool
+- Comprehensive fixture support
+
+This architecture provides a robust, secure, and extensible foundation for Claude-GitHub integration while maintaining clear separation of concerns and comprehensive error handling.