refactor(go): make daily metric totals opt in

docs/architecture/storage-minimal-contract.md

@@ -44,6 +44,7 @@
    - 原因：日统计是正式业务指标，应只统计已经定位到 VIN 的车辆。
    - 无 VIN 的 JT808 等数据保留在 raw/Redis/session 中用于排查和待绑定，不进入正式车辆指标。
    - 状态：schema 使用 `PRIMARY KEY (vin, stat_date, protocol)`，不保留自增 `id` 和 `created_at`；首末总里程和样本数保留为日里程计算状态。
+   - 查询：`/api/stats/daily-metrics` 默认不执行 `COUNT(*)`，`total` 表示本页返回条数；只有报表总页数等场景传 `includeTotal=true`。
    - 生产：RDS 已在上线前删除泛化 `vehicle_daily_metric`，改为专用 `vehicle_daily_mileage`。
 
 4. `vehicle_locations` 不再接收临时身份兜底字段。

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

@@ -17,12 +17,13 @@ type Queryer interface {
 }
 
 type MetricQuery struct {
-	VIN      string
-	Protocol string
-	DateFrom string
-	DateTo   string
-	Limit    int
-	Offset   int
+	VIN          string
+	Protocol     string
+	IncludeTotal bool
+	DateFrom     string
+	DateTo       string
+	Limit        int
+	Offset       int
 }
 
 type MetricRow struct {
@@ -184,16 +185,22 @@ func (h *MetricHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		writeMetricError(w, http.StatusBadRequest, err.Error())
 		return
 	}
-	total, err := h.repository.Count(r.Context(), query)
-	if err != nil {
-		writeMetricError(w, http.StatusInternalServerError, err.Error())
-		return
+	var total int64
+	if query.IncludeTotal {
+		total, err = h.repository.Count(r.Context(), query)
+		if err != nil {
+			writeMetricError(w, http.StatusInternalServerError, err.Error())
+			return
+		}
 	}
 	rows, err := h.repository.Query(r.Context(), query)
 	if err != nil {
 		writeMetricError(w, http.StatusInternalServerError, err.Error())
 		return
 	}
+	if !query.IncludeTotal {
+		total = int64(len(rows))
+	}
 	w.Header().Set("Content-Type", "application/json")
 	_ = json.NewEncoder(w).Encode(map[string]any{
 		"items":  rows,
@@ -214,12 +221,13 @@ func parseMetricQuery(r *http.Request) (MetricQuery, error) {
 		return MetricQuery{}, err
 	}
 	query := MetricQuery{
-		VIN:      values.Get("vin"),
-		Protocol: values.Get("protocol"),
-		DateFrom: values.Get("dateFrom"),
-		DateTo:   values.Get("dateTo"),
-		Limit:    limit,
-		Offset:   offset,
+		VIN:          values.Get("vin"),
+		Protocol:     values.Get("protocol"),
+		IncludeTotal: strings.EqualFold(strings.TrimSpace(values.Get("includeTotal")), "true"),
+		DateFrom:     values.Get("dateFrom"),
+		DateTo:       values.Get("dateTo"),
+		Limit:        limit,
+		Offset:       offset,
 	}
 	if !validDate(query.DateFrom) || !validDate(query.DateTo) {
 		return MetricQuery{}, errors.New("dateFrom/dateTo must use YYYY-MM-DD")

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

@@ -75,7 +75,7 @@ func TestMetricHandlerReturnsDailyMetrics(t *testing.T) {
 		))
 
 	handler := NewMetricHandler(NewMetricRepository(db))
-	request := httptest.NewRequest(http.MethodGet, "/api/stats/daily-metrics?vin=LB9A32A21R0LS1707&protocol=GB32960&dateFrom=2020-07-01&dateTo=2020-07-01", nil)
+	request := httptest.NewRequest(http.MethodGet, "/api/stats/daily-metrics?vin=LB9A32A21R0LS1707&protocol=GB32960&dateFrom=2020-07-01&dateTo=2020-07-01&includeTotal=true", nil)
 	response := httptest.NewRecorder()
 
 	handler.ServeHTTP(response, request)
@@ -103,9 +103,6 @@ func TestMetricHandlerReturnsEmptyItemsArrayWhenNoRows(t *testing.T) {
 		t.Fatalf("sqlmock.New() error = %v", err)
 	}
 	defer db.Close()
-	mock.ExpectQuery("SELECT COUNT\\(\\*\\) FROM vehicle_daily_mileage").
-		WithArgs("YUTONG_MQTT").
-		WillReturnRows(sqlmock.NewRows([]string{"total"}).AddRow(0))
 	mock.ExpectQuery("SELECT vin, stat_date, protocol, daily_mileage_km, first_total_mileage_km, latest_total_mileage_km, sample_count, updated_at FROM vehicle_daily_mileage").
 		WithArgs("YUTONG_MQTT", 50, 0).
 		WillReturnRows(sqlmock.NewRows([]string{
@@ -132,6 +129,41 @@ func TestMetricHandlerReturnsEmptyItemsArrayWhenNoRows(t *testing.T) {
 	}
 }
 
+func TestMetricHandlerSkipsTotalCountByDefault(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("sqlmock.New() error = %v", err)
+	}
+	defer db.Close()
+	mock.ExpectQuery("SELECT vin, stat_date, protocol, daily_mileage_km, first_total_mileage_km, latest_total_mileage_km, sample_count, updated_at FROM vehicle_daily_mileage").
+		WithArgs("JT808", 1, 0).
+		WillReturnRows(sqlmock.NewRows([]string{
+			"vin", "stat_date", "protocol", "daily_mileage_km",
+			"first_total_mileage_km", "latest_total_mileage_km", "sample_count",
+			"updated_at",
+		}).AddRow(
+			"LKLG7C4E3NA774736", "2026-07-02", "JT808", 12.3,
+			8792.8, 8805.1, 30, "2026-07-02 23:59:59",
+		))
+
+	handler := NewMetricHandler(NewMetricRepository(db))
+	request := httptest.NewRequest(http.MethodGet, "/api/stats/daily-metrics?protocol=JT808&limit=1", nil)
+	response := httptest.NewRecorder()
+
+	handler.ServeHTTP(response, request)
+
+	if response.Code != http.StatusOK {
+		t.Fatalf("status = %d body=%s", response.Code, response.Body.String())
+	}
+	body := response.Body.String()
+	if !strings.Contains(body, `"total":1`) {
+		t.Fatalf("response should use page size as total when total count is not requested: %s", body)
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Fatalf("sql expectations: %v", err)
+	}
+}
+
 func TestMetricHandlerRejectsInvalidPagination(t *testing.T) {
 	handler := NewMetricHandler(NewMetricRepository(&sql.DB{}))
 	request := httptest.NewRequest(http.MethodGet, "/api/stats/daily-metrics?limit=2001", nil)