beacon v2 discovery: advertise metamesh.core + service resources on 239.255.99.1:9099, /api/neighbors ?cap= filter

internal/api/handlers.go

@@ -550,11 +550,11 @@ func (s *Server) handleGetFileByCID(w http.ResponseWriter, r *http.Request) {
 
 // handleListNeighbors handles GET /neighbors and GET /api/neighbors.
 //
-// meta-discovery v1. The list is built from UDP announces held in memory, not
-// from files under /meta-core/services, so it works across stacks that share a
-// network but no volume. Instances of the same service are collapsed to the
-// most recent, which preserves the one-row-per-service shape the old
-// /api/services had. `?all=1` returns every instance, for debugging.
+// Beacon v2 (docs/project-architecture/beacon-v2.md). The list is this node's
+// in-memory view of the UDP group, so it works across stacks that share a
+// network but no volume. Instances of one name collapse to the most recent
+// (one row per service, the nav menu's shape); `?all=1` returns every
+// instance, `?cap=<pattern>` keeps only nodes with a matching capability.
 func (s *Server) handleListNeighbors(w http.ResponseWriter, r *http.Request) {
 	response := map[string]interface{}{
 		"current":   s.config.ServiceName,
@@ -576,6 +576,15 @@ func (s *Server) handleListNeighbors(w http.ResponseWriter, r *http.Request) {
 	} else {
 		list = s.mesh.NeighborsByName()
 	}
+	if pattern := r.URL.Query().Get("cap"); pattern != "" {
+		kept := list[:0]
+		for _, nb := range list {
+			if nb.Matches(pattern) {
+				kept = append(kept, nb)
+			}
+		}
+		list = kept
+	}
 
 	response["enabled"] = true
 	response["neighbors"] = list

internal/api/server.go

@@ -43,7 +43,7 @@ type Server struct {
 	// challenges backs proof-of-possession on reveal/delete. In-process, so a
 	// restart invalidates the ones in flight — see identity/challenge.go.
 	challenges *identity.ChallengeStore
-	// mesh is the UDP discovery node (meta-discovery v1). nil when discovery
+	// mesh is the UDP discovery node (beacon v2). nil when discovery
 	// is disabled or failed to bind, in which case /api/neighbors reports an
 	// empty list rather than erroring — a dashboard nav is decoration and
 	// must not take the API down with it.
@@ -291,7 +291,7 @@ func (s *Server) setupRoutes() {
 	s.router.HandleFunc("/api/events/files", s.handleEventsFiles).Methods("GET")
 	s.router.HandleFunc("/api/events/meta", s.handleEventsMeta).Methods("GET")
 
-	// meta-discovery v1: neighbours heard over UDP. Supersedes /api/services,
+	// beacon v2: neighbours heard over UDP. Supersedes /api/services,
 	// which is still served above while consumers migrate.
 	s.router.HandleFunc("/neighbors", s.handleListNeighbors).Methods("GET")
 	s.router.HandleFunc("/api/neighbors", s.handleListNeighbors).Methods("GET")