feat: implement tiered billing expression evaluation and related functionality

- Added support for tiered billing expressions in the billing system.
- Introduced new types and functions for handling billing expressions, including caching and execution.
- Updated existing billing logic to accommodate tiered billing scenarios.
- Enhanced request handling to support incoming billing expression requests.
- Added tests for tiered billing functionality to ensure correctness.

service/billing_session.go

@@ -27,6 +27,8 @@ type BillingSession struct {
 	funding          FundingSource
 	preConsumedQuota int  // 实际预扣额度（信任用户可能为 0）
 	tokenConsumed    int  // 令牌额度实际扣减量
+	extraReserved    int  // 发送前补充预扣的额度（订阅退款时需要单独回滚）
+	trusted          bool // 是否命中信任额度旁路
 	fundingSettled   bool // funding.Settle 已成功，资金来源已提交
 	settled          bool // Settle 全部完成（资金 + 令牌）
 	refunded         bool // Refund 已调用
@@ -97,6 +99,8 @@ func (s *BillingSession) Refund(c *gin.Context) {
 	tokenKey := s.relayInfo.TokenKey
 	isPlayground := s.relayInfo.IsPlayground
 	tokenConsumed := s.tokenConsumed
+	extraReserved := s.extraReserved
+	subscriptionId := s.relayInfo.SubscriptionId
 	funding := s.funding
 
 	gopool.Go(func() {
@@ -104,6 +108,11 @@ func (s *BillingSession) Refund(c *gin.Context) {
 		if err := funding.Refund(); err != nil {
 			common.SysLog("error refunding billing source: " + err.Error())
 		}
+		if extraReserved > 0 && funding.Source() == BillingSourceSubscription && subscriptionId > 0 {
+			if err := model.PostConsumeUserSubscriptionDelta(subscriptionId, -int64(extraReserved)); err != nil {
+				common.SysLog("error refunding subscription extra reserved quota: " + err.Error())
+			}
+		}
 		// 2) 退还令牌额度
 		if tokenConsumed > 0 && !isPlayground {
 			if err := model.IncreaseTokenQuota(tokenId, tokenKey, tokenConsumed); err != nil {
@@ -140,6 +149,34 @@ func (s *BillingSession) GetPreConsumedQuota() int {
 	return s.preConsumedQuota
 }
 
+func (s *BillingSession) Reserve(targetQuota int) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if s.settled || s.refunded || s.trusted || targetQuota <= s.preConsumedQuota {
+		return nil
+	}
+
+	delta := targetQuota - s.preConsumedQuota
+	if delta <= 0 {
+		return nil
+	}
+
+	if err := s.reserveFunding(delta); err != nil {
+		return err
+	}
+	if err := s.reserveToken(delta); err != nil {
+		s.rollbackFundingReserve(delta)
+		return err
+	}
+
+	s.preConsumedQuota += delta
+	s.tokenConsumed += delta
+	s.extraReserved += delta
+	s.syncRelayInfo()
+	return nil
+}
+
 // ---------------------------------------------------------------------------
 // PreConsume — 统一预扣费入口（含信任额度旁路）
 // ---------------------------------------------------------------------------
@@ -151,6 +188,7 @@ func (s *BillingSession) preConsume(c *gin.Context, quota int) *types.NewAPIErro
 
 	// ---- 信任额度旁路 ----
 	if s.shouldTrust(c) {
+		s.trusted = true
 		effectiveQuota = 0
 		logger.LogInfo(c, fmt.Sprintf("用户 %d 额度充足, 信任且不需要预扣费 (funding=%s)", s.relayInfo.UserId, s.funding.Source()))
 	} else if effectiveQuota > 0 {
@@ -191,6 +229,55 @@ func (s *BillingSession) preConsume(c *gin.Context, quota int) *types.NewAPIErro
 	return nil
 }
 
+func (s *BillingSession) reserveFunding(delta int) error {
+	switch funding := s.funding.(type) {
+	case *WalletFunding:
+		if err := model.DecreaseUserQuota(funding.userId, delta); err != nil {
+			return types.NewError(err, types.ErrorCodeUpdateDataError, types.ErrOptionWithSkipRetry())
+		}
+		funding.consumed += delta
+		return nil
+	case *SubscriptionFunding:
+		if err := model.PostConsumeUserSubscriptionDelta(funding.subscriptionId, int64(delta)); err != nil {
+			return types.NewErrorWithStatusCode(
+				fmt.Errorf("订阅额度不足或未配置订阅: %s", err.Error()),
+				types.ErrorCodeInsufficientUserQuota,
+				http.StatusForbidden,
+				types.ErrOptionWithSkipRetry(),
+				types.ErrOptionWithNoRecordErrorLog(),
+			)
+		}
+		return nil
+	default:
+		return types.NewError(fmt.Errorf("unsupported funding source: %s", s.funding.Source()), types.ErrorCodeUpdateDataError, types.ErrOptionWithSkipRetry())
+	}
+}
+
+func (s *BillingSession) rollbackFundingReserve(delta int) {
+	switch funding := s.funding.(type) {
+	case *WalletFunding:
+		if err := model.IncreaseUserQuota(funding.userId, delta, false); err != nil {
+			common.SysLog("error rolling back wallet funding reserve: " + err.Error())
+		} else {
+			funding.consumed -= delta
+		}
+	case *SubscriptionFunding:
+		if err := model.PostConsumeUserSubscriptionDelta(funding.subscriptionId, -int64(delta)); err != nil {
+			common.SysLog("error rolling back subscription funding reserve: " + err.Error())
+		}
+	}
+}
+
+func (s *BillingSession) reserveToken(delta int) error {
+	if delta <= 0 || s.relayInfo.IsPlayground {
+		return nil
+	}
+	if err := PreConsumeTokenQuota(s.relayInfo, delta); err != nil {
+		return types.NewErrorWithStatusCode(err, types.ErrorCodePreConsumeTokenQuotaFailed, http.StatusForbidden, types.ErrOptionWithSkipRetry(), types.ErrOptionWithNoRecordErrorLog())
+	}
+	return nil
+}
+
 // shouldTrust 统一信任额度检查，适用于钱包和订阅。
 func (s *BillingSession) shouldTrust(c *gin.Context) bool {
 	// 异步任务（ForcePreConsume=true）必须预扣全额，不允许信任旁路
@@ -235,10 +322,10 @@ func (s *BillingSession) syncRelayInfo() {
 
 	if sub, ok := s.funding.(*SubscriptionFunding); ok {
 		info.SubscriptionId = sub.subscriptionId
-		info.SubscriptionPreConsumed = sub.preConsumed
+		info.SubscriptionPreConsumed = sub.preConsumed + int64(s.extraReserved)
 		info.SubscriptionPostDelta = 0
 		info.SubscriptionAmountTotal = sub.AmountTotal
-		info.SubscriptionAmountUsedAfterPreConsume = sub.AmountUsedAfter
+		info.SubscriptionAmountUsedAfterPreConsume = sub.AmountUsedAfter + int64(s.extraReserved)
 		info.SubscriptionPlanId = sub.PlanId
 		info.SubscriptionPlanTitle = sub.PlanTitle
 	} else {