Pending or dead-lettered → Discarded now. In flight → cancelled (03 §7): both flags come back true, the handler is aborted within one heartbeat interval, and the row becomes Discarded when it acknowledges.
The autoscaler metric. Both numbers matter: schedulers subtract running executions from the metric, so a claimable-only count scales to zero while work is still in flight and starves the queue (02 §4.4a).
Validates operator input and maps between the transport contract (03 §5.2) and the Remote Operation I/O types (03 §8). Every validation failure throws before any transport call.