2.15.4

Direct workflow-bound service updates now reject a zero completion timeout with a typed validation error before storing a call or evaluating admission. Blank and padded completion modes use the shared wait policy.

Accepted-only calls, keyed submissions and existing transactions retain their bounded behavior. Replays return the original call. Query zero waits and unresolved-catalog auditing keep their existing contracts.

Includes regression coverage and documentation for the completion/accepted-only distinction. See PR #951 and #947.