RuntimeError: Task attached to a different loop

Root cause

Background dispatcher task was created during a session-scoped FastAPI app/client fixture before pytest-asyncio reset or replaced the running event loop for the individual test. The webhook request then awaited a task bound to the stale session loop from the function-scoped test loop.

Minimal fix

Make the async app/client fixture function-scoped, ensure FastAPI lifespan startup runs inside the same event loop used by the test, and explicitly await startup/shutdown around the AsyncClient. For example, use a function-scoped pytest_asyncio fixture with LifespanManager(app) or ASGITransport(lifespan='on') so app.state.dispatcher creates its background task on the active test loop.