antigravity-claude-proxy/CLAUDE.md

CLAUDE.md

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

Project Overview

Antigravity Claude Proxy is a Node.js proxy server that exposes an Anthropic-compatible API backed by Antigravity's Cloud Code service. It enables using Claude models (claude-sonnet-4-5-thinking, claude-opus-4-5-thinking) and Gemini models (gemini-3-flash, gemini-3-pro-low, gemini-3-pro-high) with Claude Code CLI.

The proxy translates requests from Anthropic Messages API format → Google Generative AI format → Antigravity Cloud Code API, then converts responses back to Anthropic format with full thinking/streaming support.

Commands

# Install dependencies
npm install

# Start server (runs on port 8080)
npm start

# Start with model fallback enabled (falls back to alternate model when quota exhausted)
npm start -- --fallback

# Start with debug logging
npm start -- --debug

# Start with file watching for development
npm run dev

# Account management
npm run accounts         # Interactive account management
npm run accounts:add     # Add a new Google account via OAuth
npm run accounts:add -- --no-browser  # Add account on headless server (manual code input)
npm run accounts:list    # List configured accounts
npm run accounts:verify  # Verify account tokens are valid

# Run all tests (server must be running on port 8080)
npm test

# Run individual tests
npm run test:signatures    # Thinking signatures
npm run test:multiturn     # Multi-turn with tools
npm run test:streaming     # Streaming SSE events
npm run test:interleaved   # Interleaved thinking
npm run test:images        # Image processing
npm run test:caching       # Prompt caching
npm run test:crossmodel    # Cross-model thinking signatures
npm run test:oauth         # OAuth no-browser mode

Architecture

Request Flow:

Claude Code CLI → Express Server (server.js) → CloudCode Client → Antigravity Cloud Code API

Directory Structure:

src/
├── index.js                    # Entry point
├── server.js                   # Express server
├── constants.js                # Configuration values
├── errors.js                   # Custom error classes
├── fallback-config.js          # Model fallback mappings and helpers
│
├── cloudcode/                  # Cloud Code API client
│   ├── index.js                # Public API exports
│   ├── session-manager.js      # Session ID derivation for caching
│   ├── rate-limit-parser.js    # Parse reset times from headers/errors
│   ├── request-builder.js      # Build API request payloads
│   ├── sse-parser.js           # Parse SSE for non-streaming
│   ├── sse-streamer.js         # Stream SSE events in real-time
│   ├── message-handler.js      # Non-streaming message handling
│   ├── streaming-handler.js    # Streaming message handling
│   └── model-api.js            # Model listing and quota APIs
│
├── account-manager/            # Multi-account pool management
│   ├── index.js                # AccountManager class facade
│   ├── storage.js              # Config file I/O and persistence
│   ├── selection.js            # Account picking (round-robin, sticky)
│   ├── rate-limits.js          # Rate limit tracking and state
│   └── credentials.js          # OAuth token and project handling
│
├── auth/                       # Authentication
│   ├── oauth.js                # Google OAuth with PKCE
│   ├── token-extractor.js      # Legacy token extraction from DB
│   └── database.js             # SQLite database access
│
├── webui/                      # Web Management Interface
│   └── index.js                # Express router and API endpoints
│
├── cli/                        # CLI tools
│   └── accounts.js             # Account management CLI
│
├── format/                     # Format conversion (Anthropic ↔ Google)
│   ├── index.js                # Re-exports all converters
│   ├── request-converter.js    # Anthropic → Google conversion
│   ├── response-converter.js   # Google → Anthropic conversion
│   ├── content-converter.js    # Message content conversion
│   ├── schema-sanitizer.js     # JSON Schema cleaning for Gemini
│   ├── thinking-utils.js       # Thinking block validation/recovery
│   └── signature-cache.js      # Signature cache (tool_use + thinking signatures)
│
└── utils/                      # Utilities
    ├── helpers.js              # formatDuration, sleep
    ├── logger.js               # Structured logging
    └── native-module-helper.js # Auto-rebuild for native modules

Frontend Structure (public/):

public/
├── index.html                  # Main entry point
├── js/
│   ├── app.js                  # Main application logic (Alpine.js)
│   ├── store.js                # Global state management
│   ├── components/             # UI Components
│   │   ├── dashboard.js        # Real-time stats & charts
│   │   ├── account-manager.js  # Account list & OAuth handling
│   │   ├── logs-viewer.js      # Live log streaming
│   │   └── claude-config.js    # CLI settings editor
│   └── utils/                  # Frontend utilities
└── views/                      # HTML partials (loaded dynamically)
    ├── dashboard.html
    ├── accounts.html
    ├── settings.html
    └── logs.html

Key Modules:

• src/server.js: Express server exposing Anthropic-compatible endpoints (/v1/messages, /v1/models, /health, /account-limits) and mounting WebUI
• src/webui/index.js: WebUI backend handling API routes (/api/*) for config, accounts, and logs
• src/cloudcode/: Cloud Code API client with retry/failover logic, streaming and non-streaming support
• src/account-manager/: Multi-account pool with sticky selection, rate limit handling, and automatic cooldown
• src/auth/: Authentication including Google OAuth, token extraction, database access, and auto-rebuild of native modules
• src/format/: Format conversion between Anthropic and Google Generative AI formats
• src/constants.js: API endpoints, model mappings, fallback config, OAuth config, and all configuration values
• src/fallback-config.js: Model fallback mappings (getFallbackModel(), hasFallback())
• src/errors.js: Custom error classes (RateLimitError, AuthError, ApiError, etc.)

Multi-Account Load Balancing:

• Sticky account selection for prompt caching (stays on same account across turns)
• Model-specific rate limiting via account.modelRateLimits[modelId]
• Automatic switch only when rate-limited for > 2 minutes on the current model
• Session ID derived from first user message hash for cache continuity
• Account state persisted to ~/.config/antigravity-proxy/accounts.json

Prompt Caching:

• Cache is organization-scoped (requires same account + session ID)
• Session ID is SHA256 hash of first user message content (stable across turns)
• cache_read_input_tokens returned in usage metadata when cache hits
• Token calculation: input_tokens = promptTokenCount - cachedContentTokenCount

Model Fallback (--fallback flag):

• When all accounts are exhausted for a model, automatically falls back to an alternate model
• Fallback mappings defined in MODEL_FALLBACK_MAP in src/constants.js
• Thinking models fall back to thinking models (e.g., claude-sonnet-4-5-thinking → gemini-3-flash)
• Fallback is disabled on recursive calls to prevent infinite chains
• Enable with npm start -- --fallback or FALLBACK=true environment variable

Cross-Model Thinking Signatures:

• Claude and Gemini use incompatible thinking signatures
• When switching models mid-conversation, incompatible signatures are detected and dropped
• Signature cache tracks model family ('claude' or 'gemini') for each signature
• hasGeminiHistory() detects Gemini→Claude cross-model scenarios
• Thinking recovery (closeToolLoopForThinking()) injects synthetic messages to close interrupted tool loops
• For Gemini targets: strict validation - drops unknown or mismatched signatures
• For Claude targets: lenient - lets Claude validate its own signatures

Native Module Auto-Rebuild:

• When Node.js is updated, native modules like better-sqlite3 may become incompatible
• The proxy automatically detects NODE_MODULE_VERSION mismatch errors
• On detection, it attempts to rebuild the module using npm rebuild
• If rebuild succeeds, the module is reloaded; if reload fails, a server restart is required
• Implementation in src/utils/native-module-helper.js and lazy loading in src/auth/database.js

Web Management UI:

• Stack: Vanilla JS + Alpine.js + Tailwind CSS (via CDN)
• Architecture: Single Page Application (SPA) with dynamic view loading
• State Management: Alpine.store for global state (accounts, settings, logs)
• Features:
  • Real-time dashboard with Chart.js visualization
  • OAuth flow handling via popup window
  • Live log streaming via Server-Sent Events (SSE)
  • Config editor for both Proxy and Claude CLI (~/.claude/settings.json)
• Security: Optional password protection via WEBUI_PASSWORD env var

Testing Notes

• Tests require the server to be running (npm start in separate terminal)
• Tests are CommonJS files (.cjs) that make HTTP requests to the local proxy
• Shared test utilities are in tests/helpers/http-client.cjs
• Test runner supports filtering: node tests/run-all.cjs <filter> to run matching tests

Code Organization

Constants: All configuration values are centralized in src/constants.js:

• API endpoints and headers
• Model mappings and model family detection (getModelFamily(), isThinkingModel())
• Model fallback mappings (MODEL_FALLBACK_MAP)
• OAuth configuration
• Rate limit thresholds
• Thinking model settings

Model Family Handling:

• getModelFamily(model) returns 'claude' or 'gemini' based on model name
• Claude models use signature field on thinking blocks
• Gemini models use thoughtSignature field on functionCall parts (cached or sentinel value)
• When Claude Code strips thoughtSignature, the proxy tries to restore from cache, then falls back to skip_thought_signature_validator

Error Handling: Use custom error classes from src/errors.js:

• RateLimitError - 429/RESOURCE_EXHAUSTED errors
• AuthError - Authentication failures
• ApiError - Upstream API errors
• Helper functions: isRateLimitError(), isAuthError()

Utilities: Shared helpers in src/utils/helpers.js:

• formatDuration(ms) - Format milliseconds as "1h23m45s"
• sleep(ms) - Promise-based delay
• isNetworkError(error) - Check if error is a transient network error

Logger: Structured logging via src/utils/logger.js:

• logger.info(msg) - Standard info (blue)
• logger.success(msg) - Success messages (green)
• logger.warn(msg) - Warnings (yellow)
• logger.error(msg) - Errors (red)
• logger.debug(msg) - Debug output (magenta, only when enabled)
• logger.setDebug(true) - Enable debug mode
• logger.isDebugEnabled - Check if debug mode is on

WebUI APIs:

• /api/accounts/* - Account management (list, add, remove, refresh)
• /api/config/* - Server configuration (read/write)
• /api/claude/config - Claude CLI settings
• /api/logs/stream - SSE endpoint for real-time logs
• /api/auth/url - Generate Google OAuth URL

Maintenance

When making significant changes to the codebase (new modules, refactoring, architectural changes), update this CLAUDE.md and the README.md file to keep documentation in sync.