rows LockResultRow (1); a timeout raises an error IsTransientDatabaseError recognises.
One Pending delivery per row, at most DELIVERY_INSERT_CHUNK per call.
Inserts when no message has this ID; rows MessageInsertedRow (0 = a message with this ID already exists).
Per-transaction setup the platform needs before taking publish-order locks; null when none.
Takes a free or expired key, or re-takes this MessageID's own Reserved row; rows ReservationRow it now owns (0–1).
Calls used while publishing and by the deduplication ledger.