Every serving principal may answer the services discovery for what it serves; the controller announces its seat (hq ADR 0197)

Grants: a principal that serves tools subscribes $SRV.PING/$SRV.INFO and those questions under
each name it serves — its own and no other's; the tool runtime and people may ask. The controller
answers discovery for the mesh-controller seat in NATS's services format, one endpoint per verb it
serves, with the seat's description and schema. module list --json says which modules declare tools,
so the console expects an announcement only from those.

internal/broker/nats.go

@@ -236,6 +236,8 @@ func PermissionsFor(p Principal) (Permissions, error) {
 		// which this package mirrors rather than reads, and a verb the seat does not declare is a
 		// subject nothing publishes.
 		sub = append(sub, "mesh.seat."+ControllerSeat+".tool.>")
+		// And says so (novox/hq ADR 0197): it answers discovery for the seat it serves.
+		sub = append(sub, announcing(ControllerSeat)...)
 
 		// The two events it reacts to, and its ack subject on the stream they arrive from
 		// (streams.go). **Each named, not a pattern**: `mesh.mod.*.event.>` would make the
@@ -271,6 +273,9 @@ func PermissionsFor(p Principal) (Permissions, error) {
 			return Permissions{}, err
 		}
 		pub = append(pub, invoked...)
+		// And may ask what answers (novox/hq ADR 0197): a question every service answers about
+		// itself, its replies to the asker's own inbox.
+		pub = append(pub, discovering()...)
 
 	case KindEnrolment:
 		// A leaked token is useless for anything but enrolling: it cannot read a declaration, hear
@@ -327,6 +332,15 @@ func PermissionsFor(p Principal) (Permissions, error) {
 		// away — no other principal may subscribe this namespace, and a caller's authority is
 		// still granted per tool, by name, on the publish side.
 		sub = append(sub, own+".tool.>")
+		// It says what it serves (novox/hq ADR 0197): discovery for its own name and every seat it
+		// holds a verb of, answered by the runtime that serves them.
+		announced := []string{p.Module}
+		for _, s := range p.Holds {
+			if len(s.Serves) > 0 {
+				announced = append(announced, s.Name)
+			}
+		}
+		sub = append(sub, announcing(announced...)...)
 		// Its own membership (ADR 0160): the one subject a runtime derives for itself, read
 		// directly from the stream and followed live. Nothing else's.
 		sub = append(sub, MembershipSubject(p.Node, p.Module))
@@ -413,11 +427,16 @@ func PermissionsFor(p Principal) (Permissions, error) {
 		// module's own principal has, for the same reason: the tools a module serves are what its
 		// code answers, and a list here would be a second copy of it. Each held seat's verbs on
 		// this node, as the holder's own principal would be granted them.
+		var serves []string
 		for _, d := range p.Carries {
 			if !safeSubject.MatchString(d.Module) {
 				return Permissions{}, fmt.Errorf(
 					"%q cannot be part of a subject: a permission is a subject pattern, and this would widen it", d.Module)
 			}
+			serves = append(serves, d.Module)
+			for _, s := range d.Holds {
+				serves = append(serves, s.Name)
+			}
 			own := "mesh.mod." + d.Module
 			sub = append(sub, own+".tool.>")
 			// A tool that emits an event is the module's code and emits under the module's name
@@ -444,6 +463,10 @@ func PermissionsFor(p Principal) (Permissions, error) {
 			return Permissions{}, err
 		}
 		pub = append(pub, invoked...)
+		// It says what it serves and may ask what answers (novox/hq ADR 0197): the runtime answers
+		// discovery for each module and seat it carries, and the console it is asks the bus.
+		sub = append(sub, announcing(serves...)...)
+		pub = append(pub, discovering()...)
 		// Nothing about consumers: it consumes nothing. A module's reactions to events are its
 		// own long-lived process, which ADR 0175 leaves where it is; what moves here is tools.
 		sub = unique(sub)
@@ -765,3 +788,23 @@ func invokedSubjects(invokes []string) ([]string, error) {
 	}
 	return out, nil
 }
+
+// announcing is what a principal that serves tools subscribes to answer the NATS services
+// protocol's discovery (novox/hq ADR 0197): the questions asked of every service, and those asked of
+// each name it serves — its own and no other's, so it cannot answer for a service it is not.
+func announcing(names ...string) []string {
+	out := []string{"$SRV.PING", "$SRV.INFO"}
+	for _, n := range names {
+		if !safeSubject.MatchString(n) {
+			continue
+		}
+		out = append(out, "$SRV.PING."+n, "$SRV.PING."+n+".>", "$SRV.INFO."+n, "$SRV.INFO."+n+".>")
+	}
+	return out
+}
+
+// discovering is what a principal publishes to ask what answers (novox/hq ADR 0197): the services
+// protocol's discovery requests, whose replies come to its own inbox.
+func discovering() []string {
+	return []string{"$SRV.PING", "$SRV.PING.>", "$SRV.INFO", "$SRV.INFO.>"}
+}