fix(go): preserve sparse realtime location fields

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

@@ -223,6 +223,23 @@ func TestRealtimeUpsertsDoNotOverwriteWithOlderEventTime(t *testing.T) {
 	}
 }
 
+func TestRealtimeLocationUpsertKeepsExistingSparseFieldsWhenMQTTOnlySendsCoordinates(t *testing.T) {
+	for _, column := range []string{
+		"speed_kmh",
+		"total_mileage_km",
+		"soc_percent",
+		"altitude_m",
+		"direction_deg",
+		"alarm_flag",
+		"status_flag",
+	} {
+		want := column + " = IF(VALUES(event_time) IS NOT NULL AND (vehicle_realtime_location.event_time IS NULL OR VALUES(event_time) >= vehicle_realtime_location.event_time), COALESCE(VALUES(" + column + "), " + column + "), " + column + ")"
+		if !strings.Contains(upsertRealtimeLocationSQL, want) {
+			t.Fatalf("location upsert should keep existing %s when incoming sparse MQTT frame omits it; missing:\n%s\nin:\n%s", column, want, upsertRealtimeLocationSQL)
+		}
+	}
+}
+
 func TestSnapshotWriterBackfillsPlateFromBindingByVIN(t *testing.T) {
 	exec := &recordingSnapshotExec{}
 	resolver := &recordingPlateResolver{plate: "沪A12345"}