handOff

Hands message to the local receivers, only while every routed receiver is subscribed and open for processing.

Completes as soon as the message entered the local sink (LocalHandoff.accepted) or could not (LocalHandoff.REFUSED: no routable receiver, a full or closed sink); it never waits for a receiver's demand. LocalHandoff.admission then tells whether every routed receiver admitted it. The conservative default refuses, which disables local-first routing.