fix(billing): 异步任务退款时同步减少 used_quota (#6795)

* fix(billing): 异步任务退款时同步减少 used_quota
退款时仅恢复了 quota（剩余额度），但未同步减少 used_quota（已用额度），
导致"总额度"（quota + used_quota）随退款次数持续虚增，超出用户实际充值金额。

修复三处退款路径：
- RefundTaskQuota：任务失败完整退款
- RecalculateTaskQuota：差额结算退款分支
- controller/midjourney.go：Midjourney 任务失败退款

新增 model.UpdateUserUsedQuota 公开函数，仅调整 used_quota 不影响 request_count。

* fix(billing): 任务退款时同步扣减渠道 used_quota

* fix(billing): complete async task refund accounting

* style(model): group internal Midjourney fields

---------

Co-authored-by: CaIon <i@caion.me>

service/midjourney.go

@@ -3,6 +3,8 @@ package service
 import (
 	"context"
 	"encoding/json"
+	"errors"
+	"fmt"
 	"io"
 	"net/http"
 	"strconv"
@@ -13,6 +15,8 @@ import (
 	"github.com/QuantumNous/new-api/constant"
 	"github.com/QuantumNous/new-api/dto"
 	"github.com/QuantumNous/new-api/logger"
+	"github.com/QuantumNous/new-api/model"
+	relaycommon "github.com/QuantumNous/new-api/relay/common"
 	relayconstant "github.com/QuantumNous/new-api/relay/constant"
 	"github.com/QuantumNous/new-api/setting"
 
@@ -27,6 +31,113 @@ func CovertMjpActionToModelName(mjAction string) string {
 	return modelName
 }
 
+// PrepareMidjourneyTaskBilling sets the durable refund marker before the task is inserted.
+func PrepareMidjourneyTaskBilling(relayInfo *relaycommon.RelayInfo, task *model.Midjourney, quota int, shouldBill bool) (bool, error) {
+	if task == nil {
+		return false, errors.New("Midjourney task is nil")
+	}
+	task.Quota = 0
+	task.TokenId = 0
+	task.BillingChannelId = 0
+	if !shouldBill {
+		return false, nil
+	}
+	if relayInfo == nil {
+		return false, errors.New("relay info is nil")
+	}
+	if quota < 0 {
+		return false, errors.New("quota cannot be negative")
+	}
+	if relayInfo.BillingSource == BillingSourceSubscription {
+		return false, errors.New("legacy Midjourney billing does not support subscriptions")
+	}
+
+	task.Quota = quota
+	task.BillingChannelId = task.ChannelId
+	if relayInfo.ChannelMeta != nil && relayInfo.ChannelId > 0 {
+		task.BillingChannelId = relayInfo.ChannelId
+	}
+	return true, nil
+}
+
+// SettleMidjourneyTaskBilling charges a persisted legacy task and records the applied stages.
+func SettleMidjourneyTaskBilling(relayInfo *relaycommon.RelayInfo, task *model.Midjourney, prepared bool) (bool, error) {
+	if !prepared {
+		return false, nil
+	}
+	if relayInfo == nil {
+		return false, errors.New("relay info is nil")
+	}
+	if task == nil || task.Id == 0 {
+		return false, errors.New("Midjourney task must be persisted before billing")
+	}
+
+	result, billingErr := postConsumeQuotaWithResult(relayInfo, task.Quota, 0, true)
+	if !result.FundingApplied {
+		task.Quota = 0
+		task.TokenId = 0
+		task.BillingChannelId = 0
+		if updateErr := task.UpdateBillingState(); updateErr != nil {
+			return false, errors.Join(billingErr, fmt.Errorf("clear Midjourney billing state: %w", updateErr))
+		}
+		return false, billingErr
+	}
+
+	task.TokenId = 0
+	if result.TokenApplied {
+		task.TokenId = relayInfo.TokenId
+	}
+	if updateErr := task.UpdateBillingState(); updateErr != nil {
+		return true, errors.Join(billingErr, fmt.Errorf("update Midjourney billing state: %w", updateErr))
+	}
+	return true, billingErr
+}
+
+// RefundMidjourneyQuota reverses every accounting element recorded for a billed legacy task.
+func RefundMidjourneyQuota(ctx context.Context, task *model.Midjourney, reason string) bool {
+	quota := task.Quota
+	if quota == 0 {
+		return true
+	}
+
+	if err := model.IncreaseUserQuota(task.UserId, quota, false); err != nil {
+		logger.LogWarn(ctx, fmt.Sprintf("退还 Midjourney 用户额度失败 task %s: %s", task.MjId, err.Error()))
+		return false
+	}
+
+	if task.TokenId > 0 {
+		tokenKey := resolveTokenKey(ctx, task.TokenId, task.MjId)
+		if tokenKey != "" {
+			if err := model.IncreaseTokenQuota(task.TokenId, tokenKey, quota); err != nil {
+				logger.LogWarn(ctx, fmt.Sprintf("退还 Midjourney 令牌额度失败 task %s: %s", task.MjId, err.Error()))
+			}
+		}
+	}
+
+	billingChannelId := task.GetBillingChannelId()
+	model.UpdateUserUsedQuota(task.UserId, -quota)
+	model.UpdateChannelUsedQuota(billingChannelId, -quota)
+	model.RecordTaskBillingLog(model.RecordTaskBillingLogParams{
+		UserId:    task.UserId,
+		LogType:   model.LogTypeRefund,
+		Content:   "",
+		ChannelId: billingChannelId,
+		ModelName: CovertMjpActionToModelName(task.Action),
+		Quota:     quota,
+		TokenId:   task.TokenId,
+		Other: map[string]interface{}{
+			"task_id": task.MjId,
+			"reason":  reason,
+		},
+	})
+
+	task.Quota = 0
+	if err := task.UpdateBillingState(); err != nil {
+		logger.LogError(ctx, fmt.Sprintf("Midjourney 退款成功但清除 quota 失败 task %s: %s", task.MjId, err.Error()))
+	}
+	return true
+}
+
 func GetMjRequestModel(relayMode int, midjRequest *dto.MidjourneyRequest) (string, *dto.MidjourneyResponse, bool) {
 	action := ""
 	if relayMode == relayconstant.RelayModeMidjourneyAction {