- BackfillRequested now maps to BackfillFollower domain event (not FollowAccepted);
worker calls run_backfill_for_follower to send LOCAL content to new follower inbox,
instead of incorrectly trying to import from an inbox URL as if it were an outbox
- reviews broadcast as Create activity instead of Add (semantically correct)
- also_known_as JSON parse failure logs warning + preserves raw string as single-element
vec instead of silently returning empty