Deliver again an ask the controller made, removing the original from its queue (issue 334)

A build ask its seat's worker gave up on could only be dropped, though the
controller already holds the publish on that seat's accepts and the stream
API to remove the original. Asks to other seats stay refused: delivering them
needs a grant ADR 0264 withholds, in the asker's name ADR 0259 protects.

internal/broker/nats.go

@@ -163,6 +163,21 @@ type Principal struct {
 // goes with the retired seat row.
 var seatsTheControllerAsks = []string{"node-build-agent", "mesh-build-machine"}
 
+// TheControllersAsk says whether a message of stream, published on subject, is an ask the controller
+// itself makes: one on the accept subject of a seat in seatsTheControllerAsks, kept in that seat's own
+// work queue. Such an ask, given up on by the seat's worker, can be delivered again with the authority
+// the controller already holds — the publish on that seat's accepts and the stream API to remove the
+// original — and no other can (novox/hq issue 334, ADR 0264's consequences: no grant over the seats'
+// queues).
+func TheControllersAsk(stream, subject string) bool {
+	for _, seat := range seatsTheControllerAsks {
+		if stream == seatStreamName(seat) && strings.HasPrefix(subject, "mesh.seat."+seat+".accept.") {
+			return true
+		}
+	}
+	return false
+}
+
 // SeatVerb is one verb of one seat, on every machine holding it.
 type SeatVerb struct{ Seat, Verb string }