fix(scheduler): ignore stale executor success after defer reschedule

[Pedrinhonitz]

Summary

Fixes a race where the trigger resumes a deferred task to scheduled before the scheduler processes the executor SUCCESS from the worker defer exit. The scheduler then treated scheduled vs executor success as a state mismatch and failed the TI (#66374).

Changes

• In process_executor_events, treat executor SUCCESS while the TI is SCHEDULED with next_method set (same try) as a stale defer-exit event, consistent with the existing “requeued after defer” intent.
• Add test_process_executor_events_stale_success_when_scheduled_after_defer (positive + negative without next_method).
• Add newsfragment 66374.bugfix.rst.

Testing

pytest airflow-core/tests/unit/jobs/test_scheduler_job.py::TestSchedulerJob::test_process_executor_events_stale_success_when_scheduled_after_defer -q

• closes: Race condition between scheduler processing events and trigger completion #66374

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[jscheffl]

Looks good for me. Thanks for the fix!

As I am not 100% deep in the scheduler feel not comfortable to mege, so if there is a second pair of eyes from reviewer would be cool, else LGTM!

[Pedrinhonitz]

Perfect!

I'm also eagerly awaiting another review and am open to other suggestions for resolving this issue.

Thank you for your review.