The message provenance.
The event payload.
ReadonlysignalAborts when the sender stops waiting for a reply.
The topic that carries the message.
Refuses the message: the sender's awaited emit() rejects with a
MessageBusError whose code is code, 'REFUSED' by default. A host that
passes the message on refuses with 'NO_RESPONDER' when nothing can answer it, and with
'HANDLER_THREW' when what it passed the message to threw. Ignored, with a warning, once
the reply has already settled.
Optionalmessage: stringOptionalcode: "NO_RESPONDER" | "HANDLER_THREW" | "REFUSED"
A message delivered to an event topic responder.