Summarize VPN fabric stream sharding health

agents/rap-node-agent/internal/vpnruntime/fabric_session_transport.go

@@ -281,10 +281,16 @@ func (t *FabricSessionPacketTransport) Snapshot() map[string]any {
 		sendFramesByStream[fmt.Sprintf("%d", streamID)] = count
 	}
 	t.statsMu.Unlock()
+	streamIDsByClass := copyStreamIDsByTrafficClass(t.StreamIDsByTrafficClass)
 	return map[string]any{
 		"schema_version":           "rap.vpn_fabric_session_packet_transport.v1",
 		"stream_id":                t.StreamID,
-		"stream_ids_by_class":      copyStreamIDsByTrafficClass(t.StreamIDsByTrafficClass),
+		"stream_ids_by_class":      streamIDsByClass,
+		"stream_class_count":       len(streamIDsByClass),
+		"stream_shard_count":       countStreamIDs(streamIDsByClass) + len(t.StreamIDs),
+		"send_class_count":         countNonZeroStringUint64Values(sendFramesByClass),
+		"send_stream_count":        countNonZeroStringUint64Values(sendFramesByStream),
+		"sharding_active":          len(streamIDsByClass) > 1 || countStreamIDs(streamIDsByClass)+len(t.StreamIDs) > 1,
 		"send_frames_by_class":     sendFramesByClass,
 		"send_packets_by_class":    sendPacketsByClass,
 		"send_frames_by_stream_id": sendFramesByStream,
@@ -322,3 +328,21 @@ func copyStreamIDsByTrafficClass(values map[string][]uint64) map[string][]uint64
 	}
 	return out
 }
+
+func countStreamIDs(values map[string][]uint64) int {
+	total := 0
+	for _, ids := range values {
+		total += len(ids)
+	}
+	return total
+}
+
+func countNonZeroStringUint64Values(values map[string]uint64) int {
+	total := 0
+	for _, value := range values {
+		if value > 0 {
+			total++
+		}
+	}
+	return total
+}

agents/rap-node-agent/internal/vpnruntime/fabric_transport_test.go

@@ -265,6 +265,13 @@ func TestFabricSessionPacketTransportShardsStreamsByTrafficClass(t *testing.T) {
 	if snapshot["schema_version"] != "rap.vpn_fabric_session_packet_transport.v1" {
 		t.Fatalf("snapshot schema missing: %+v", snapshot)
 	}
+	if snapshot["stream_class_count"] != 2 ||
+		snapshot["stream_shard_count"] != 4 ||
+		snapshot["send_class_count"] != 2 ||
+		snapshot["send_stream_count"] != 2 ||
+		snapshot["sharding_active"] != true {
+		t.Fatalf("unexpected shard summary: %+v", snapshot)
+	}
 	framesByClass := snapshot["send_frames_by_class"].(map[string]uint64)
 	if framesByClass[FabricTrafficClassBulk] != 1 || framesByClass[FabricTrafficClassInteractive] != 1 {
 		t.Fatalf("send frames by class = %+v", framesByClass)