POST /tasks/{id}/complete does not persist done status

[venkataramasu]

Summary

POST /tasks/{task_id}/complete reports success but does not persist completed state.

Intended outcome

After completing a task, a follow-up GET /tasks/{id} should show status=done and a non-null completed_at.

Actual outcome

Completion response shows done, but subsequent fetch still shows open.

Reproduction steps

1. Install deps: python3 -m pip install -r requirements.txt
2. Run tests: pytest -v tests/test_api.py
3. Observe failure in test_complete_task_persists_done_state

Repro logs

tests/test_api.py::test_complete_task_persists_done_state FAILED

>       assert refreshed_response.json()["status"] == "done"
E       AssertionError: assert 'open' == 'done'

Notes

This currently fails in HTTP-level tests and indicates persistence is not updated on completion.