RuntimeError: Task attached to a different loop

Root cause

Background task and asyncio.Queue are initialized during FastAPI startup from a session-scoped async fixture, then pytest-asyncio replaces the event loop for the test function. The webhook handler later awaits Queue.put() on objects bound to the stale session loop, producing a cross-loop RuntimeError.

Minimal fix

Make the FastAPI app/client fixture function-scoped, ensure pytest-asyncio uses a function-scoped event loop, and drive the app lifespan inside the fixture so startup completes on the same loop as each test. For example, remove any session-scoped event_loop override, set asyncio_default_fixture_loop_scope = function, and create the AsyncClient inside `async with LifespanManager(app): ...` before yielding it.