0181 — A deliveries row exists only while a message needs individual attention; success is no row

Context. On the cursor path a failing message used to drag its whole range down, and the happy path’s zero-rows-per-success property ruled out materializing a row per message just to track the rare failure.

Decision. Commit takes two slices — MessageException (retryable) and MessageTerminal (unrecoverable) — and records only those: one sparse deliveries row per failing message, exceptions inserted as ready, terminals as dead. Status collapses to ready | inflight | dead with no done: a happy-path success writes nothing, and when a recorded exception later succeeds, RecordExceptionSuccess deletes its row rather than flipping a status. The range’s lease always frees regardless of individual outcomes — one bad message no longer fails its batch-mates.

Consequences. Row existence is itself the “still needs attention” signal; resolved exceptions leave no trace in deliveries, and only dead rows persist, as the dead-letter record. The row is the handoff between the range-claim happy path and the per-row retry state machine — it exists exactly as long as a message needs individual treatment.