fix(gateway): 完善 thinking block 重试和 cache nil 检查

- 使用 FilterThinkingBlocksForRetry 替代 FilterThinkingBlocks
- count_tokens 增加 thinking block 签名错误重试
- cache nil 检查防止空指针
- shouldBill 逻辑修复避免重复扣费
- 移除 debug 日志

backend/internal/service/gateway_service.go

@@ -541,7 +541,7 @@ func (s *GatewayService) SelectAccountWithLoadAwareness(ctx context.Context, gro
 			for _, item := range available {
 				result, err := s.tryAcquireAccountSlot(ctx, item.account.ID, item.account.Concurrency)
 				if err == nil && result.Acquired {
-					if sessionHash != "" {
+					if sessionHash != "" && s.cache != nil {
 						_ = s.cache.SetSessionAccountID(ctx, sessionHash, item.account.ID, stickySessionTTL)
 					}
 					return &AccountSelectionResult{
@@ -577,7 +577,7 @@ func (s *GatewayService) tryAcquireByLegacyOrder(ctx context.Context, candidates
 	for _, acc := range ordered {
 		result, err := s.tryAcquireAccountSlot(ctx, acc.ID, acc.Concurrency)
 		if err == nil && result.Acquired {
-			if sessionHash != "" {
+			if sessionHash != "" && s.cache != nil {
 				_ = s.cache.SetSessionAccountID(ctx, sessionHash, acc.ID, stickySessionTTL)
 			}
 			return &AccountSelectionResult{
@@ -708,7 +708,7 @@ func sortAccountsByPriorityAndLastUsed(accounts []*Account, preferOAuth bool) {
 func (s *GatewayService) selectAccountForModelWithPlatform(ctx context.Context, groupID *int64, sessionHash string, requestedModel string, excludedIDs map[int64]struct{}, platform string) (*Account, error) {
 	preferOAuth := platform == PlatformGemini
 	// 1. 查询粘性会话
-	if sessionHash != "" {
+	if sessionHash != "" && s.cache != nil {
 		accountID, err := s.cache.GetSessionAccountID(ctx, sessionHash)
 		if err == nil && accountID > 0 {
 			if _, excluded := excludedIDs[accountID]; !excluded {
@@ -781,7 +781,7 @@ func (s *GatewayService) selectAccountForModelWithPlatform(ctx context.Context,
 	}
 
 	// 4. 建立粘性绑定
-	if sessionHash != "" {
+	if sessionHash != "" && s.cache != nil {
 		if err := s.cache.SetSessionAccountID(ctx, sessionHash, selected.ID, stickySessionTTL); err != nil {
 			log.Printf("set session account failed: session=%s account_id=%d err=%v", sessionHash, selected.ID, err)
 		}
@@ -797,7 +797,7 @@ func (s *GatewayService) selectAccountWithMixedScheduling(ctx context.Context, g
 	preferOAuth := nativePlatform == PlatformGemini
 
 	// 1. 查询粘性会话
-	if sessionHash != "" {
+	if sessionHash != "" && s.cache != nil {
 		accountID, err := s.cache.GetSessionAccountID(ctx, sessionHash)
 		if err == nil && accountID > 0 {
 			if _, excluded := excludedIDs[accountID]; !excluded {
@@ -873,7 +873,7 @@ func (s *GatewayService) selectAccountWithMixedScheduling(ctx context.Context, g
 	}
 
 	// 4. 建立粘性绑定
-	if sessionHash != "" {
+	if sessionHash != "" && s.cache != nil {
 		if err := s.cache.SetSessionAccountID(ctx, sessionHash, selected.ID, stickySessionTTL); err != nil {
 			log.Printf("set session account failed: session=%s account_id=%d err=%v", sessionHash, selected.ID, err)
 		}
@@ -1022,8 +1022,8 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 				if s.isThinkingBlockSignatureError(respBody) {
 					log.Printf("Account %d: detected thinking block signature error, retrying with filtered thinking blocks", account.ID)
 
-					// 过滤thinking blocks并重试
+					// 过滤thinking blocks并重试（使用更激进的过滤）
-					filteredBody := FilterThinkingBlocks(body)
+					filteredBody := FilterThinkingBlocksForRetry(body)
 					retryReq, buildErr := s.buildUpstreamRequest(ctx, c, account, filteredBody, token, tokenType, reqModel)
 					if buildErr == nil {
 						retryResp, retryErr := s.httpUpstream.Do(retryReq, proxyURL, account.ID, account.Concurrency)
@@ -1303,10 +1303,13 @@ func (s *GatewayService) isThinkingBlockSignatureError(respBody []byte) bool {
 		return false
 	}
 
-	// 检测thinking block签名相关的错误
+	// 检测signature相关的错误（更宽松的匹配）
-	// 例如: "Invalid `signature` in `thinking` block"
+	// 例如: "Invalid `signature` in `thinking` block", "***.signature" 等
-	return (strings.Contains(msg, "thinking") || strings.Contains(msg, "thought")) &&
+	if strings.Contains(msg, "signature") {
-		strings.Contains(msg, "signature")
+		return true
+	}
+
+	return false
 }
 
 func (s *GatewayService) shouldFailoverOn400(respBody []byte) bool {
@@ -1751,7 +1754,8 @@ func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInpu
 		usageLog.SubscriptionID = &subscription.ID
 	}
 
-	if err := s.usageLogRepo.Create(ctx, usageLog); err != nil {
+	inserted, err := s.usageLogRepo.Create(ctx, usageLog)
+	if err != nil {
 		log.Printf("Create usage log failed: %v", err)
 	}
 
@@ -1761,10 +1765,12 @@ func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInpu
 		return nil
 	}
 
+	shouldBill := inserted || err != nil
+
 	// 根据计费类型执行扣费
 	if isSubscriptionBilling {
 		// 订阅模式：更新订阅用量（使用 TotalCost 原始费用，不考虑倍率）
-		if cost.TotalCost > 0 {
+		if shouldBill && cost.TotalCost > 0 {
 			if err := s.userSubRepo.IncrementUsage(ctx, subscription.ID, cost.TotalCost); err != nil {
 				log.Printf("Increment subscription usage failed: %v", err)
 			}
@@ -1773,7 +1779,7 @@ func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInpu
 		}
 	} else {
 		// 余额模式：扣除用户余额（使用 ActualCost 考虑倍率后的费用）
-		if cost.ActualCost > 0 {
+		if shouldBill && cost.ActualCost > 0 {
 			if err := s.userRepo.DeductBalance(ctx, user.ID, cost.ActualCost); err != nil {
 				log.Printf("Deduct balance failed: %v", err)
 			}
@@ -1843,17 +1849,35 @@ func (s *GatewayService) ForwardCountTokens(ctx context.Context, c *gin.Context,
 		s.countTokensError(c, http.StatusBadGateway, "upstream_error", "Request failed")
 		return fmt.Errorf("upstream request failed: %w", err)
 	}
-	defer func() {
-		_ = resp.Body.Close()
-	}()
 
 	// 读取响应体
 	respBody, err := io.ReadAll(resp.Body)
+	_ = resp.Body.Close()
 	if err != nil {
 		s.countTokensError(c, http.StatusBadGateway, "upstream_error", "Failed to read response")
 		return err
 	}
 
+	// 检测 thinking block 签名错误（400）并重试一次（过滤 thinking blocks）
+	if resp.StatusCode == 400 && s.isThinkingBlockSignatureError(respBody) {
+		log.Printf("Account %d: detected thinking block signature error on count_tokens, retrying with filtered thinking blocks", account.ID)
+
+		filteredBody := FilterThinkingBlocks(body)
+		retryReq, buildErr := s.buildCountTokensRequest(ctx, c, account, filteredBody, token, tokenType, reqModel)
+		if buildErr == nil {
+			retryResp, retryErr := s.httpUpstream.Do(retryReq, proxyURL, account.ID, account.Concurrency)
+			if retryErr == nil {
+				resp = retryResp
+				respBody, err = io.ReadAll(resp.Body)
+				_ = resp.Body.Close()
+				if err != nil {
+					s.countTokensError(c, http.StatusBadGateway, "upstream_error", "Failed to read response")
+					return err
+				}
+			}
+		}
+	}
+
 	// 处理错误响应
 	if resp.StatusCode >= 400 {
 		// 标记账号状态（429/529等）