RuntimeError: Task attached to a different loop

Root cause

Background retry worker task was created during a session-scoped FastAPI app fixture before pytest-asyncio replaced/reset the running event loop for the individual async test. The queue's readiness task belongs to the old loop, but the HTTPX ASGI request executes on the function test loop.

Minimal fix

Change the app/client async fixtures to function scope so startup runs on the same loop as each test, and explicitly await FastAPI lifespan startup before yielding the AsyncClient. Avoid creating asyncio tasks at import time or in session-scoped fixtures; create the retry_queue worker inside startup on the active pytest loop and cancel/await it during shutdown.