Setting-mutation idempotency receipts were written with an expires_at that
nothing enforced, so the table grew forever. Add a hidden daily system task
(05:00) that walks every login account, opens its user store, and calls
DeleteExpiredSettingMutations. A user whose store fails to open or sweep is
logged and skipped so one broken store cannot stall retention for everyone
else; the delete is idempotent, so the next run repairs anything missed.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
