[Airflow 3 / Task SDK] Heartbeat 404 "Task Instance not found" after ~12h run; supervisor SERVER_TERMINATED (SIGKILL); retry sees 409 while TI still running

### Under which category would you file this issue? Task SDK ### Apache Airflow version airflow 3.0.6 ### What happened and how to reproduce it? During a long-running task (wall time on the order of ~12 hours in our case), the task process was terminated by the supervisor after the execution API stopped accepting heartbeats: - PUT /execution/task-instances/<ti_uuid>/heartbeat returned 404 with Task Instance not found / reason: not_found. - Supervisor logged that the server indicated the task should not keep running, then Task killed! with process SIGKILL (exit_code=-9), final_state=SERVER_TERMINATED. - Supervisor also logged duration ~ 43214 s (~12 h) for that workload session. In the same log window we also saw PATCH .../task-instances/<ti_uuid>/run return 409 Conflict with a message along the lines of cannot start task instance — invalid state, previous_state=running (exact try_number in our export was 2; we treat that as illustrative, not the core claim—we care about 404 + forced termination after a long running execute, regardless of attempt index). DAG/operator architecture: The workload is a PythonOperator subclass whose execute() submits work to Snowflake and then blocks inside the same task on an imperative wait() (implemented on a BaseSensorOperator subclass: time.sleep + polling). There is no separate sensor task, so one TI can stay running for many hours. What I need help with: 1. Under what conditions does the Task Execution API return 404 on heartbeat for a TI that was recently updating heartbeats successfully? 2. Whether long running tasks on Celery + Airflow 3 are expected to hit this, and how it relates to timeouts, TI lifecycle, or DAG run / span updates (we also see scheduler INFO such as Found span_status 'should_end', while updating state for dag_run ... on the same run). 3. Recommended patterns for multi-hour waits (deferrable operators, separate sensor task, etc.) under the Task SDK. Representative log excerpts: `PUT /execution/task-instances/<…