Separate webhook acceptance from downstream delivery

Treat webhook request acceptance and downstream channel delivery as separate outcomes. If one identifiable fanout starts correlated side effects, a sibling success plus absence of a reliably observable caller failure can support an inference of HTTP acceptance; it does not prove destination delivery.

Persist per-destination queued, sent, and failed events with provider, opaque destination identity, correlation ID, and HTTP outcome. Verify destination receipt separately. Missing success telemetry, log loss, and providers that accept before failing downstream remain explicit limits.