Undo a previous end-user merge: reads the merge ledger and re-points every FK row (events, insights, tasks, …) back to its original end-user, un-tombstoning the folded-in sources. Safe to retry — a second undo of the same merge changes nothing (it fails with already_reverted). Use to correct a wrong identity merge (merges stay reversible for 30 days). Find the event_id with list_identity_merges (pick an un-reverted merge); event_id is required.
Connector