- Add _ClassificationError sentinel raised by _run() for classification failures
- Add _mark_classification_failed() async helper for final status writeback
- Change decorator to bind=True, max_retries=3
- Outer sync task catches _ClassificationError and calls self.retry(countdown=[30,90,270])
- MaxRetriesExceededError caught in nested try/except to avoid re-raise from exc block
- Promote test_retry_backoff and test_exhaustion_sets_failed_status from xfail to passing
- Tests use push_request(retries=N) + patch.object(task, "retry") to verify countdown values
- test_exhaustion_sets_failed_status uses assert_called_once_with (asyncio.run calling convention)