Failure event handlers not triggered with multiple workers

When running Luigi pipelines with multiple workers, task failure event handlers registered with @luigi.Task.event_handler(luigi.Event.FAILURE) do not execute when tasks fail. The same handlers work correctly when running with a single worker.

Run Luigi with a single worker if failure event handling is critical for logging or cleanup. Alternatively, implement failure handling directly in task code rather than relying on event handlers for multi-worker deployments.