fix(mileage): recover sparse source daily distance

go/vehicle-gateway/internal/stats/gps_mileage_test.go

@@ -87,6 +87,70 @@ func TestGPSMileagePointFromEnvelopeUsesNaturalDayAndStableSource(t *testing.T)
 	}
 }
 
+func TestGPSMileagePointFromYutongEnvelopeRequiresMovement(t *testing.T) {
+	loc := time.FixedZone("Asia/Shanghai", 8*3600)
+	eventTime := time.Date(2026, 7, 19, 8, 0, 0, 0, loc)
+	env := envelope.FrameEnvelope{
+		EventID:        "evt-yutong-gps",
+		Protocol:       envelope.ProtocolYutongMQTT,
+		VIN:            "LMRKH9AC9R1004099",
+		DeviceID:       "LMRKH9AC9R1004099",
+		SourceEndpoint: "mqtt://yutong/ytforward/shln/2",
+		EventTimeMS:    eventTime.UnixMilli(),
+		Fields: map[string]any{
+			"yutong_mqtt.data.longitude":   121.4737,
+			"yutong_mqtt.data.latitude":    31.2304,
+			"yutong_mqtt.data.meter_speed": 18,
+		},
+	}
+	identity := SourceIdentity{
+		Protocol:     envelope.ProtocolYutongMQTT,
+		SourceIP:     "mqtt",
+		SourceCode:   "yutong",
+		SourceKind:   "PLATFORM",
+		PlatformName: "宇通",
+	}
+	point, ok := GPSMileagePointFromEnvelope(env, identity, loc)
+	if !ok {
+		t.Fatal("moving Yutong location must be eligible for GPS mileage fallback")
+	}
+	if point.Protocol != envelope.ProtocolYutongMQTT || point.SourceKey != "YUTONG_MQTT:LMRKH9AC9R1004099@PLATFORM:yutong" {
+		t.Fatalf("point = %+v", point)
+	}
+	env.Fields["yutong_mqtt.data.meter_speed"] = 0
+	if _, ok := GPSMileagePointFromEnvelope(env, identity, loc); ok {
+		t.Fatal("stationary Yutong jitter must not enter GPS mileage fallback")
+	}
+}
+
+func TestWriterThrottlesHighFrequencyGPSMileageStateWrites(t *testing.T) {
+	writer := NewWriter(&recordingExec{}, time.FixedZone("Asia/Shanghai", 8*3600))
+	writer.SetGPSAccumulationInterval(10 * time.Second)
+	start := time.Date(2026, 7, 19, 8, 0, 0, 0, time.FixedZone("Asia/Shanghai", 8*3600))
+	point := GPSMileagePoint{
+		VIN:       "LMRKH9AC9R1004099",
+		StatDate:  "2026-07-19",
+		Protocol:  envelope.ProtocolYutongMQTT,
+		SourceKey: "YUTONG_MQTT:LMRKH9AC9R1004099@PLATFORM:yutong",
+		EventTime: start,
+	}
+	if !writer.shouldAccumulateGPS(point) {
+		t.Fatal("first point must be accepted")
+	}
+	writer.markGPSAccumulated(point)
+	point.EventTime = start.Add(5 * time.Second)
+	if writer.shouldAccumulateGPS(point) {
+		t.Fatal("high-frequency point inside the 10s interval must be throttled")
+	}
+	point.EventTime = start.Add(11 * time.Second)
+	if !writer.shouldAccumulateGPS(point) {
+		t.Fatal("point after the 10s interval must be accepted")
+	}
+	if got := writer.CacheStats().GPSAccumulationEntries; got != 1 {
+		t.Fatalf("GPS cache entries = %d, want 1", got)
+	}
+}
+
 func TestAccumulateJT808GPSMileagePersistsEstimateAndProjects(t *testing.T) {
 	db, mock, err := sqlmock.New()
 	if err != nil {