The worker a holder bound was a push consumer in a queue group with one ask in flight: right for
one holder, and with two it would still be a queue of one — the server hands a pushed ask to
whichever subscriber it picks, busy or not, and the in-flight cap is per consumer, not per holder.
Now the worker is pulled: every machine holding the seat binds the same durable and fetches one
ask when it has finished the last, so an idle machine is the one that takes the next, the asks in
flight are bounded by the holders working, and nothing is delivered that nobody asked for — which
is also what ended the race issue 186 describes. A holder's grants trade the delivery subject for
MSG.NEXT on the worker; the ack grant and the heartbeat that keeps a long build alive stay.
Proven against a real bus: the build round trip, a backlog taken by a machine that arrives later,
and work handed back by one machine coming round again.
jochen
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