The node agent keeps the bus server unless the want carries the warrant's mark, and the bus's have says what the server runs (ADR 0594 §2-§4, §6)

internal/selfcompose/selfcompose.go

@@ -1163,6 +1163,30 @@ func (c *Composer) Policy(ctx context.Context, module string) string {
 	return policy
 }
 
+// BusServer is, for a module whose manifest provides the mesh's bus, the ids it declares of the bus server's resources
+// (catalogue.BusServerOf, novox/hq ADR 0594 §7), none for any other; known says whether the manifest could be read.
+func (c *Composer) BusServer(ctx context.Context, module string) (ids []string, known bool) {
+	c.mu.Lock()
+	m, ok := c.modules[module]
+	c.mu.Unlock()
+	if !ok || m.Manifest == "" {
+		return nil, false
+	}
+	raw, err := reader{c: c}.Manifest(ctx, m.Manifest)
+	if err != nil {
+		return nil, false
+	}
+	parsed, held, err := c.taken(module, m, raw)
+	if err != nil || held != "" {
+		return nil, false
+	}
+	for id := range catalogue.BusServerOf(parsed) {
+		ids = append(ids, id)
+	}
+	sort.Strings(ids)
+	return ids, true
+}
+
 // HoldsData says whether a module's manifest declares data (catalogue.Manifest.DataItems), as a composition's Data says
 // it, and whether the manifest could be read: the agent's Data for what runs of a module from the kept declaration
 // (agent.Env.HoldsData, issue 924).