Cancellation failure history event has empty instance_id and execution_id=0 in payload

[pinodeca]

Summary

When df.cancel(instance_id, reason) cancels a workflow, the final cancellation-related failure event can contain an empty instance_id and execution_id=0 in the JSON event payload.

The history row itself may still be associated with the correct instance, but consumers that inspect the event payload directly lose the link between the cancellation event and the instance.

Expected behavior

The final cancellation/failure event payload should include the same instance_id and execution identifier as the cancellation request and the history row that contains the event.

Actual behavior

The cancellation request event includes the expected identifiers, but the subsequent failure/cancelled terminal event payload can contain:

{
  "instance_id": "",
  "execution_id": 0
}

Repro shape

1. Start a workflow that waits or sleeps long enough to cancel.
2. Call df.cancel(instance_id, reason).
3. Inspect recent rows in duroxide.history for that instance.
4. Compare the identifiers in the cancellation request event with the identifiers in the terminal failure/cancelled event payload.

Impact

Telemetry or diagnostic pipelines that read event payloads directly cannot reliably correlate cancellation terminal events back to the workflow instance.