Verify bounded VPN fabric fanout

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

@@ -329,6 +329,32 @@ func TestFabricSessionPacketTransportSplitsMixedBatchByStream(t *testing.T) {
 	}
 }
 
+func TestFabricSessionPacketTransportFanoutBoundedByConfiguredStreams(t *testing.T) {
+	sender := &captureFabricSessionSender{}
+	transport := &FabricSessionPacketTransport{
+		Sender:          sender,
+		VPNConnectionID: "vpn-1",
+		SendDirection:   FabricDirectionClientToGateway,
+		StreamIDsByTrafficClass: map[string][]uint64{
+			FabricTrafficClassBulk: []uint64{901, 902, 903, 904},
+		},
+	}
+	var packets [][]byte
+	for port := uint16(10000); port < 10100; port++ {
+		packets = append(packets, testIPv4TCPPacket([4]byte{10, 77, 0, 2}, [4]byte{192, 168, 200, 95}, port, 443))
+	}
+	if err := transport.SendGatewayPacketBatch(context.Background(), packets); err != nil {
+		t.Fatalf("send large flow batch: %v", err)
+	}
+	if len(sender.frames) > 4 {
+		t.Fatalf("fanout = %d, want bounded by 4 streams", len(sender.frames))
+	}
+	snapshot := transport.Snapshot()
+	if snapshot["max_batch_frame_count"].(uint64) > 4 {
+		t.Fatalf("max fanout not bounded: %+v", snapshot)
+	}
+}
+
 func TestFabricSessionPacketTransportClosesAllStreamShards(t *testing.T) {
 	sender := &captureFabricSessionSender{}
 	transport := &FabricSessionPacketTransport{

docs/architecture/DISTRIBUTED_FABRIC_NODE_PROTOCOL_PLAN.md

@@ -406,6 +406,8 @@ not collapse onto the first packet's logical stream.
 fabric-session batch and requires them to remain sharded.
 The smoke report also exposes the mixed-batch frame fanout so regressions show
 up as a concrete fanout drop, not just a failed boolean.
+Batch fanout is bounded by configured stream shards, so a large batch with many
+flows cannot explode into unbounded fabric frames.
 Fabric-session packet transport snapshots now report packets per stream plus
 last/max batch fanout, making real multi-site load distribution measurable from
 gateway status.