Two consumers may share a name; they must not share a delivery subject

novox/hq 04-ISSUES/146. A push consumer delivers onto an ordinary subject and
everything subscribed to it gets a copy. The controller holds a consumer called
'controller' on CONTROL and another called 'controller' on EVENTS, and both were
given _DELIVER.controller — so the one process, holding both subscriptions,
acted on every message twice.

Measured: one enrolment published, one message in the stream, one delivery, no
redelivery, and the controller enrolled the machine twice — the second minting a
credential that replaced the one the machine had just been handed, which is why
it then reconnected for ever as a user whose password the mesh had rotated. Every
report and every followed event doubled the same way, silently.

The stream goes in the subject because the pair is what identifies a consumer.
A subscriber's permission gains the same shape, keeping the bare name so an
existing consumer keeps working until the next assertion moves it.

internal/broker/jetstream.go

@@ -184,7 +184,20 @@ func (j *JetStream) EnsureConsumer(c Consumer) error {
 	// without the other is refused by the server with a message that does not say which half is
 	// missing.
 	if c.Queue != "" || c.Push {
-		want.DeliverSubject = "_DELIVER." + c.Name
+		// **Per consumer, which means per stream as well as per name** (novox/hq 04-ISSUES/146).
+		// A push consumer delivers onto an ordinary subject, and everything subscribed to that
+		// subject gets a copy. The controller holds a consumer called `controller` on CONTROL and
+		// another called `controller` on EVENTS, and both were given `_DELIVER.controller` — so the
+		// one process, holding both subscriptions, acted on every message twice. It enrolled a
+		// joining machine twice from one request, minting a second credential that replaced the one
+		// the machine had just been given; the same doubling applied to every report and every
+		// event the controller follows.
+		//
+		// The stream is in the name because the pair is what identifies a consumer — the server
+		// scopes a durable's name to its stream, and this subject is the only place that scoping
+		// was dropped. Already within what the controller may subscribe (`_DELIVER.controller.>`),
+		// so no permission moves.
+		want.DeliverSubject = DeliverSubjectFor(c)
 	}
 
 	switch _, err := j.js.ConsumerInfo(c.Stream, c.Name); {