fix(stats): reject sub-threshold gps drift

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) {