perf(gateway): 优化热点路径并补齐高覆盖测试

backend/internal/repository/usage_log_repo.go

@@ -915,6 +915,59 @@ func (r *usageLogRepository) GetAccountWindowStats(ctx context.Context, accountI
 	return stats, nil
 }
 
+// GetAccountWindowStatsBatch 批量获取同一窗口起点下多个账号的统计数据。
+// 返回 map[accountID]*AccountStats，未命中的账号会返回零值统计，便于上层直接复用。
+func (r *usageLogRepository) GetAccountWindowStatsBatch(ctx context.Context, accountIDs []int64, startTime time.Time) (map[int64]*usagestats.AccountStats, error) {
+	result := make(map[int64]*usagestats.AccountStats, len(accountIDs))
+	if len(accountIDs) == 0 {
+		return result, nil
+	}
+
+	query := `
+		SELECT
+			account_id,
+			COUNT(*) as requests,
+			COALESCE(SUM(input_tokens + output_tokens + cache_creation_tokens + cache_read_tokens), 0) as tokens,
+			COALESCE(SUM(total_cost * COALESCE(account_rate_multiplier, 1)), 0) as cost,
+			COALESCE(SUM(total_cost), 0) as standard_cost,
+			COALESCE(SUM(actual_cost), 0) as user_cost
+		FROM usage_logs
+		WHERE account_id = ANY($1) AND created_at >= $2
+		GROUP BY account_id
+	`
+	rows, err := r.sql.QueryContext(ctx, query, pq.Array(accountIDs), startTime)
+	if err != nil {
+		return nil, err
+	}
+	defer func() { _ = rows.Close() }()
+
+	for rows.Next() {
+		var accountID int64
+		stats := &usagestats.AccountStats{}
+		if err := rows.Scan(
+			&accountID,
+			&stats.Requests,
+			&stats.Tokens,
+			&stats.Cost,
+			&stats.StandardCost,
+			&stats.UserCost,
+		); err != nil {
+			return nil, err
+		}
+		result[accountID] = stats
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+
+	for _, accountID := range accountIDs {
+		if _, ok := result[accountID]; !ok {
+			result[accountID] = &usagestats.AccountStats{}
+		}
+	}
+	return result, nil
+}
+
 // TrendDataPoint represents a single point in trend data
 type TrendDataPoint = usagestats.TrendDataPoint