fix(go): skip empty frames in realtime snapshot

go/vehicle-gateway/internal/realtime/snapshot_writer_test.go

@@ -75,6 +75,29 @@ func TestSnapshotWriterSkipsUnknownVehicleKey(t *testing.T) {
 	}
 }
 
+func TestSnapshotWriterSkipsGB32960HeartbeatWithoutRealtimePayload(t *testing.T) {
+	exec := &recordingSnapshotExec{}
+	writer := NewSnapshotWriter(exec)
+
+	if err := writer.Update(context.Background(), envelope.FrameEnvelope{
+		Protocol:  envelope.ProtocolGB32960,
+		MessageID: "0x07",
+		VIN:       "ABCDE600000000009",
+		Parsed: map[string]any{
+			"header": map[string]any{
+				"vin":                "ABCDE600000000009",
+				"command":            "0x07",
+				"actual_body_length": 0,
+			},
+		},
+	}); err != nil {
+		t.Fatalf("Update() error = %v", err)
+	}
+	if len(exec.calls) != 0 {
+		t.Fatalf("exec calls = %d, want 0", len(exec.calls))
+	}
+}
+
 type recordingSnapshotExec struct {
 	calls []snapshotExecCall
 }