fix: align group management APIs

server/metrics/metrics.go

@@ -28,6 +28,17 @@ var (
 		Buckets: []float64{0.001, 0.003, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5},
 	}, []string{"driver", "operation", "status"})
 
+	RealtimeFanoutEventsTotal = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Name: "realtime_fanout_events_total",
+		Help: "Total number of realtime fanout events by stage, kind, target type, and status.",
+	}, []string{"stage", "kind", "target_type", "status"})
+
+	RealtimeFanoutDeliveryDuration = prometheus.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    "realtime_fanout_delivery_duration_seconds",
+		Help:    "Realtime fanout delivery age measured from message timestamp to local dispatch.",
+		Buckets: []float64{0.001, 0.003, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10},
+	}, []string{"kind", "target_type"})
+
 	WSConnectionsActive = prometheus.NewGaugeFunc(prometheus.GaugeOpts{
 		Name: "ws_connections_active",
 		Help: "Current active WebSocket connections.",
@@ -37,7 +48,8 @@ var (
 )
 
 func init() {
-	Registry.MustRegister(WSConnectionsActive, HTTPRequestsTotal, HTTPRequestDuration, DBQueryDuration)
+	Registry.MustRegister(WSConnectionsActive, HTTPRequestsTotal, HTTPRequestDuration, DBQueryDuration,
+		RealtimeFanoutEventsTotal, RealtimeFanoutDeliveryDuration)
 }
 
 func ObserveDB(driverName, operation string, started time.Time, err error) {
@@ -48,6 +60,26 @@ func ObserveDB(driverName, operation string, started time.Time, err error) {
 	DBQueryDuration.WithLabelValues(driverName, operation, status).Observe(time.Since(started).Seconds())
 }
 
+func IncRealtimeFanout(stage, kind, targetType, status string) {
+	RealtimeFanoutEventsTotal.WithLabelValues(normalizeLabel(stage), normalizeLabel(kind),
+		normalizeLabel(targetType), normalizeLabel(status)).Inc()
+}
+
+func ObserveRealtimeFanoutDelivery(kind, targetType string, timestamp time.Time) {
+	if timestamp.IsZero() {
+		return
+	}
+	RealtimeFanoutDeliveryDuration.WithLabelValues(normalizeLabel(kind), normalizeLabel(targetType)).
+		Observe(time.Since(timestamp).Seconds())
+}
+
+func normalizeLabel(value string) string {
+	if value == "" {
+		return "unknown"
+	}
+	return value
+}
+
 func expvarIntValue(name string) int64 {
 	value := expvar.Get(name)
 	if value == nil {