deliver
Deliver a single event. Realtime adapters forward to their SDK here; batch adapters typically return DeliveryOutcome.Success immediately (the event is already persisted).
Return
DeliveryOutcome.Success on success, DeliveryOutcome.RetryableFailure for transient errors (the dispatcher will retry), DeliveryOutcome.PermanentFailure for non-retryable errors (event goes to DLQ).