fix: ignore invalid zero mileage metrics

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

@@ -64,6 +64,25 @@ func TestSamplesFromEnvelopeSkipsMissingVINOrMileage(t *testing.T) {
 	}
 }
 
+func TestSamplesFromEnvelopeSkipsNonPositiveMileage(t *testing.T) {
+	for _, value := range []any{0, 0.0, -1.0, "0"} {
+		samples, err := SamplesFromEnvelope(envelope.FrameEnvelope{
+			Protocol:    envelope.ProtocolJT808,
+			VIN:         "LNBVIN00000000001",
+			EventTimeMS: time.Date(2026, 7, 1, 9, 0, 0, 0, time.FixedZone("Asia/Shanghai", 8*3600)).UnixMilli(),
+			Fields: map[string]any{
+				envelope.FieldTotalMileageKM: value,
+			},
+		}, nil)
+		if err != nil {
+			t.Fatalf("SamplesFromEnvelope(%#v) error = %v", value, err)
+		}
+		if len(samples) != 0 {
+			t.Fatalf("expected no samples for non-positive mileage %#v, got %#v", value, samples)
+		}
+	}
+}
+
 func TestWriterEnsuresSchemaAndUpsertsTwoMetrics(t *testing.T) {
 	exec := &recordingExec{}
 	writer := NewWriter(exec, time.FixedZone("Asia/Shanghai", 8*3600))
@@ -90,6 +109,9 @@ func TestWriterEnsuresSchemaAndUpsertsTwoMetrics(t *testing.T) {
 	if !strings.Contains(exec.calls[1].query, "ON DUPLICATE KEY UPDATE") {
 		t.Fatalf("unexpected upsert sql: %s", exec.calls[1].query)
 	}
+	if !strings.Contains(exec.calls[1].query, "first_total_mileage_km <= 0") {
+		t.Fatalf("upsert should ignore legacy zero first mileage: %s", exec.calls[1].query)
+	}
 }
 
 type execCall struct {