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: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

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
│
├── 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

Key Modules:

• src/server.js: Express server exposing Anthropic-compatible endpoints (/v1/messages, /v1/models, /health, /account-limits)
• 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, and database access
• 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

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

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.