refactor: batch flow upload processing (#474)

* test: cover flow upload batch semantics

* refactor: batch flow upload persistence

* refactor: batch flow upload processing

* test: harden flow upload batch regression coverage

go-backend/internal/store/repo/repository_user_quota.go

@@ -3,6 +3,7 @@ package repo
 import (
 	"errors"
 	"fmt"
+	"sort"
 	"strconv"
 	"strings"
 	"time"
@@ -255,6 +256,54 @@ func (r *Repository) AddUserQuotaUsage(userID int64, usedBytes int64, now time.T
 	return normalizeUserQuotaView(result, now), nil
 }
 
+func (r *Repository) AddUserQuotaUsageBatch(usages map[int64]int64, now time.Time) (map[int64]*model.UserQuotaView, error) {
+	if r == nil || r.db == nil {
+		return nil, errors.New("repository not initialized")
+	}
+	if len(usages) == 0 {
+		return map[int64]*model.UserQuotaView{}, nil
+	}
+
+	result := make(map[int64]*model.UserQuotaView, len(usages))
+	err := r.db.Transaction(func(tx *gorm.DB) error {
+		userIDs := make([]int64, 0, len(usages))
+		for userID := range usages {
+			if userID > 0 {
+				userIDs = append(userIDs, userID)
+			}
+		}
+		sort.Slice(userIDs, func(i, j int) bool { return userIDs[i] < userIDs[j] })
+
+		for _, userID := range userIDs {
+			q, err := r.loadOrCreateUserQuotaTx(tx, userID, now)
+			if err != nil {
+				return err
+			}
+			applyUserQuotaWindowRoll(q, now)
+			if usages[userID] > 0 {
+				q.DailyUsedBytes += usages[userID]
+				q.MonthlyUsedBytes += usages[userID]
+			}
+			q.UpdatedTime = now.UnixMilli()
+			if err := tx.Model(&model.UserQuota{}).Where("user_id = ?", userID).Updates(map[string]interface{}{
+				"daily_used_bytes":   q.DailyUsedBytes,
+				"monthly_used_bytes": q.MonthlyUsedBytes,
+				"day_key":            q.DayKey,
+				"month_key":          q.MonthKey,
+				"updated_time":       q.UpdatedTime,
+			}).Error; err != nil {
+				return err
+			}
+			result[userID] = normalizeUserQuotaView(cloneUserQuotaView(*q), now)
+		}
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return result, nil
+}
+
 func (r *Repository) MarkUserQuotaDisabled(userID int64, pausedForwardIDs []int64, now int64) error {
 	if r == nil || r.db == nil {
 		return errors.New("repository not initialized")