fix(stats): reject sub-threshold gps drift

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)
+	}
+}