emit
Suspends until the event is accepted into the outbound queue (WorkQueue → engine write buffer). Completes when enqueue succeeds; does not await transport drain.
Throws only on pre-queue rejection (e.g. reserved event names, payload encoding errors). Async transport SocketError.SendFailed after enqueue is reported on errors only — it does not fail a prior emitAwait that already returned.
Same queue semantics as emitAwait for a StreamCommand.