This FK is a denormalisation of a Job's JobNote.failure_classification. It adds some complexity at write since a JobNote must update its Job on both save and delete to reconcile Job.failure_classification to something appropriate. From an architecture perspective it makes the source of truth for a Job's failure classification not quite as clear (especially if the reconcilliation step fails). Removing this requires handling this the resulting lookup (latest JobNote or "not classified" FailureClassification) during read (happens in both the Job API and Job serialiser).