ackOutboundMessages

Acknowledge polled outbound messages. Acks are validated against the active lease and committed as a prefix-contiguous cursor advance: messages must be acknowledged in stream order. Out-of-order acks past the first gap are rejected per id (out_of_order), acks with an outdated lease token are rejected (stale_lease), and unknown ids are rejected (not_found). Acknowledged messages are never delivered again. Requires the integration:consume grant.