Historical backfills must break non-deferrable foreign-key cycles and honor write triggers

Historical backfills must account for non-deferrable foreign-key cycles and write triggers. Break an immediate cycle by inserting the first side with the cyclic reference unset, inserting the dependent row, and then patching the reference. Reconstruct rows through trigger-legal state transitions, and do not separately copy artifacts that inserts regenerate unless reconciliation proves it necessary. The exact sequence must be derived from the inspected schema and trigger contract.