Read one queue entry using ExecutionId. Parse ResultJson separately. Completed can contain a failed result; a timeout can report ErrorNumber=1041226. An empty result on a stale entry is not success. The configured cleanup timeout defaults to 36000 seconds (10 hours). Cleanup can mark an overdue entry Completed with a failed ResultJson; its message says 10 hours even if the configured timeout differs. This is distinct from retained queue history and client polling deadlines.