mir-backend-python-fastapilisted

Make It Right (FastAPI module). FastAPI + Async SQLAlchemy 2.0 + Postgres + Alembic + Redis specific reliability augmentation. Use alongside the mir-backend skill when the target stack is FastAPI — it carries the mechanical footguns that the framework-agnostic skill deliberately omits: async session lifecycle and scope, Pydantic v2 validation boundaries, Depends()-based auth and authorization, BackgroundTasks vs a real queue, async N+1 with selectinload, greenlet/sync-driver-in-async traps, Alembic migration safety on populated tables, and Redis idempotency/locking patterns. TRIGGER only when the Python backend stack is FastAPI — building, reviewing, or debugging a FastAPI endpoint, dependency, SQLAlchemy session, or Alembic migration. Always loads TOGETHER WITH mir-backend (the gates) and mir-backend-python (CPython runtime concerns: GIL, async/sync, fork-safety, cold start); this module only adds FastAPI/SQLAlchemy library mechanics. SKIP for Django, Flask, or any non-FastAPI stack (those get their own mir-
anantbhandarkar/make-it-right · ★ 12 · API & Backend · score 83

Install: claude install-skill anantbhandarkar/make-it-right

# /mir-backend-python-fastapi · Make It Right (FastAPI) Bottom tier of the chain: `mir-backend` (generic gates) → `mir-backend-python` (CPython runtime model) → **this** (FastAPI/SQLAlchemy library mechanics). Run the gates first; load the Python runtime tier for the concurrency/process model; reach for *this* at Gate 5 (design mechanics), Gate 6 (implementation), and Gate 7 review. **Runtime-level concerns (GIL, async-vs-sync, blocking the event loop, fork-safe pools, cold start) live in `mir-backend-python` — not here.** **Stack assumed:** FastAPI · SQLAlchemy 2.0 async (`AsyncSession`, `asyncpg`) · PostgreSQL · Alembic · Redis. If the project uses sync SQLAlchemy or a different DB, note the divergence before applying these. ## The FastAPI footguns AI walks into most These are the stack-specific cousins of the failure-mode catalog. Each is something async-FastAPI code gets wrong even when the *logic* is right. ### 1. Async session lifecycle — the #1 source of mystery bugs - **One `AsyncSession` per request, via a `Depends` dependency.** Never a module-level/global session — it's not concurrency-safe and you'll get cross-request data bleed or `InterfaceError`. - **Never share one session across `asyncio.gather` tasks.** A session is a single connection's unit of work; concurrent use corrupts it. Give each task its own session from the factory. - **Commit/rollback boundary belongs in the dependency or service, explicitly** — don't rely on autocommit. `expire_on_commit=Fa