advance_submissions.advance_section_id FK changed from cascadeOnDelete
to nullOnDelete; column made nullable. Aligns implementation with
RFC v0.2 §5.4 audit-immutability ("submissions remain for retention
compliance") — when ArtistEngagementObserver::deleted hard-deletes a
section, its submissions persist as orphans rather than disappearing.
Migration edited in place (branch unpushed, dev-only). Observer
docblock + test assertion updated to match. Removed pre-existing
follow-up comment that documented the deviation.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
bert.hausmans
a5190ee309