ON DELETE RESTRICT was Prisma's default for required relations;
Structure.delegation is optional (`Delegation?`), so the matching
default is ON DELETE SET NULL. Mismatch caused `prisma migrate dev`
to detect drift and prompt for a corrective migration on every run.
Caught locally on first VM-side validation. No production deployment
of #228 yet, so editing the migration in place rather than shipping a
corrective sibling - keeps the repo's migration history minimal.
Inline comment at the offending line explains the rule (nullable
Prisma relation -> SET NULL) to head off the same mistake when
ADR-0026 PR 1 adds optional FKs (Person.user, User.scopes).
Julien Gautier