fix(stats): reject sub-threshold gps drift

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

@@ -2128,7 +2128,7 @@ func TestWriterDuplicateYutongOdometerStillEntersGPSFallback(t *testing.T) {
 		EventTimeMS:    eventTime.UnixMilli(),
 		Fields: map[string]any{
 			"yutong_mqtt.data.total_mileage": 24245000,
-			"yutong_mqtt.data.longitude":     114.435672,
+			"yutong_mqtt.data.longitude":     114.436672,
 			"yutong_mqtt.data.latitude":      30.645438,
 			"yutong_mqtt.data.meter_speed":   18,
 		},

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

@@ -17,6 +17,7 @@ const (
 	gpsCoordinateSourceSuffix  = "#GPS_COORDINATE"
 	gpsMaxSegmentGap           = 10 * time.Minute
 	gpsMaxImpliedSpeedKMH      = 220.0
+	gpsMinimumDailyDistanceKM  = 0.1
 )
 
 const GPSMileageStateTableSQL = `CREATE TABLE IF NOT EXISTS vehicle_daily_gps_mileage_state (
@@ -238,7 +239,7 @@ func AccumulateGPSMileage(ctx context.Context, exec Execer, point GPSMileagePoin
 		_ = tx.Rollback()
 		return GPSMileageState{}, false, err
 	}
-	if state.UsableSegmentCount == 0 {
+	if !GPSMileageCandidateEligible(state.DailyMileageKM, state.UsableSegmentCount) {
 		if err := tx.Commit(); err != nil {
 			return GPSMileageState{}, false, err
 		}
@@ -258,6 +259,16 @@ func AccumulateGPSMileage(ctx context.Context, exec Execer, point GPSMileagePoin
 	return state, true, nil
 }
 
+// GPSMileageCandidateEligible keeps sub-100-metre stationary drift and
+// momentary speed noise in the durable accumulation state without exposing it
+// as a business daily-mileage candidate. Real movement continues accumulating
+// and becomes eligible once the evidence crosses the minimum distance.
+func GPSMileageCandidateEligible(distanceKM float64, usableSegmentCount int64) bool {
+	return usableSegmentCount > 0 &&
+		isFiniteNonNegative(distanceKM) &&
+		distanceKM >= gpsMinimumDailyDistanceKM
+}
+
 // AccumulateJT808GPSMileage remains as a compatibility wrapper for callers and
 // operational tooling compiled against the original JT808-only fallback.
 func AccumulateJT808GPSMileage(ctx context.Context, exec Execer, point GPSMileagePoint) (GPSMileageState, bool, error) {

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

@@ -151,6 +151,18 @@ func TestWriterThrottlesHighFrequencyGPSMileageStateWrites(t *testing.T) {
 	}
 }
 
+func TestGPSMileageCandidateEligibleRejectsStationaryDrift(t *testing.T) {
+	if GPSMileageCandidateEligible(0.099999, 10) {
+		t.Fatal("sub-100-metre GPS drift must not become a daily-mileage candidate")
+	}
+	if GPSMileageCandidateEligible(0.2, 0) {
+		t.Fatal("distance without a usable segment must not become a candidate")
+	}
+	if !GPSMileageCandidateEligible(0.1, 1) {
+		t.Fatal("100 metres with a usable segment should become eligible")
+	}
+}
+
 func TestAccumulateJT808GPSMileagePersistsEstimateAndProjects(t *testing.T) {
 	db, mock, err := sqlmock.New()
 	if err != nil {
@@ -250,3 +262,47 @@ func TestAccumulateJT808GPSMileageNeedsUsableSegmentBeforeProjection(t *testing.
 		t.Fatalf("unmet SQL expectations: %v", err)
 	}
 }
+
+func TestAccumulateGPSMileageKeepsSubThresholdDistanceAsStateOnly(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("sqlmock.New() error = %v", err)
+	}
+	defer db.Close()
+
+	start := time.Date(2026, 7, 20, 0, 14, 56, 0, time.FixedZone("Asia/Shanghai", 8*3600))
+	point := GPSMileagePoint{
+		VIN:       "LMRKH9ACXR1004130",
+		StatDate:  "2026-07-20",
+		Protocol:  envelope.ProtocolYutongMQTT,
+		SourceKey: "YUTONG_MQTT:LMRKH9ACXR1004130@PLATFORM:yutong",
+		SourceIP:  "mqtt",
+		EventID:   "evt-small-movement",
+		EventTime: start.Add(time.Second),
+		Longitude: 114.435573,
+		Latitude:  30.645503,
+	}
+
+	mock.ExpectBegin()
+	mock.ExpectQuery("SELECT first_event_time, latest_event_time").
+		WillReturnRows(sqlmock.NewRows([]string{
+			"first_event_time", "latest_event_time", "latest_event_id",
+			"latest_longitude", "latest_latitude", "daily_mileage_km",
+			"point_count", "usable_segment_count", "bad_jump_count",
+			"long_gap_count", "out_of_order_count",
+		}).AddRow(start, start, "evt-before", 114.435572, 30.645503, 0, 1, 0, 0, 0, 0))
+	mock.ExpectExec("UPDATE vehicle_daily_gps_mileage_state").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectCommit()
+
+	state, recovered, err := AccumulateGPSMileage(context.Background(), db, point)
+	if err != nil {
+		t.Fatalf("AccumulateGPSMileage() error = %v", err)
+	}
+	if recovered || state.DailyMileageKM <= 0 || state.DailyMileageKM >= gpsMinimumDailyDistanceKM {
+		t.Fatalf("sub-threshold state = %+v recovered=%v", state, recovered)
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Fatalf("unmet SQL expectations: %v", err)
+	}
+}