Same dependency_overrides fix as the other test_*.py commits for
get_task_executor (patch() cannot reach a route's already-registered
Depends() reference — see the conftest.py commit for the full explanation
and the empirical check that established it).
Once the mock actually intercepted the DB layer, a second, independent
defect surfaced: KeyError: 0. mock_cursor.fetchone.side_effect held 3 values
sized for "create, list, delete" (one fetchone() each), but list_tasks uses
fetchall(), not fetchone(), and delete_task has grown a second fetchone()
call since this test was written — c34db66 added the 409-on-history-loss
check, which does `row = cur.fetchone()` for the task id and then a
separate `cur.fetchone()[0]` for its execution count. A real create->list->
delete flow through this endpoint set needs 1 (create) + 2 (delete) = 3
fetchone() values in that order, not one per named step. Re-sequenced so
delete_task sees a real id and a zero execution count, reaching the intended
200 rather than an unhandled KeyError.
Source unchanged; delete_task's behavior is deliberate (c34db66) and this
integration test had not been updated to track it.