ExpressJS MCP

# express_mcp — PRD - Goal: Expose existing `express` endpoints as MCP tools with minimal config, preserving schemas/docs and reusing existing middleware for auth, inspired by FastAPI-MCP. - Reference: tadata-org/fastapi_mcp (parity in approach, not a mere OpenAPI→MCP converter). Personas - Backend Engineer: Add MCP to existing Express app with zero/low refactor. - AI/Tooling Engineer: Needs tool discovery and stable schemas for function calling. Key Requirements - Mount mode: `mcp.mount(app, '/mcp')`. - Standalone HTTP gateway: `mcp.startStandalone({ port })`. - Route discovery: Walk `app._router.stack` (incl. nested routers). - Schema preservation: - Prefer OpenAPI v3 if provided. - Per-route annotations (zod/JSON Schema). - Fallback inference to permissive object. - Auth bridging: Use existing middleware chain during dispatch. - In-process transport: Synthetic req/res through middleware and handler (no HTTP). - Observability: Structured logs and error mapping. Non-Goals - Not a generic OpenAPI→MCP-only generator. - No framework migration. Acceptance Criteria - Mount and standalone gateway work. - Tools reflect schemas from OpenAPI/annotations when present. - Auth middleware enforces 401/403 as in HTTP. - 90%+ unit coverage on core modules (discovery, dispatch, schemas, gateway). Reference - FastAPI-MCP: https://github.com/tadata-org/fastapi_mcp