perf(gateway): 优化负载感知调度

主要改进：
- 优化负载感知调度的准确性和响应速度
- 将 AccountUsageService 的包级缓存改为依赖注入
- 修复 SSE/JSON 转义和 nil 安全问题
- 恢复 Google One 功能兼容性

backend/internal/service/gateway_service.go

@@ -905,7 +905,7 @@ func (s *GatewayService) GetAccessToken(ctx context.Context, account *Account) (
 	case AccountTypeOAuth, AccountTypeSetupToken:
 		// Both oauth and setup-token use OAuth token flow
 		return s.getOAuthToken(ctx, account)
-	case AccountTypeAPIKey:
+	case AccountTypeApiKey:
 		apiKey := account.GetCredential("api_key")
 		if apiKey == "" {
 			return "", "", errors.New("api_key not found in credentials")
@@ -976,7 +976,7 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 
 	// 应用模型映射（仅对apikey类型账号）
 	originalModel := reqModel
-	if account.Type == AccountTypeAPIKey {
+	if account.Type == AccountTypeApiKey {
 		mappedModel := account.GetMappedModel(reqModel)
 		if mappedModel != reqModel {
 			// 替换请求体中的模型名
@@ -1013,8 +1013,37 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 			return nil, fmt.Errorf("upstream request failed: %w", err)
 		}
 
-		// 检查是否需要重试
-		if resp.StatusCode >= 400 && s.shouldRetryUpstreamError(account, resp.StatusCode) {
+		// 优先检测thinking block签名错误（400）并重试一次
+		if resp.StatusCode == 400 {
+			respBody, readErr := io.ReadAll(io.LimitReader(resp.Body, 2<<20))
+			if readErr == nil {
+				_ = resp.Body.Close()
+
+				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
+					filteredBody := FilterThinkingBlocks(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)
+						if retryErr == nil {
+							// 使用重试后的响应，继续后续处理
+							resp = retryResp
+							break
+						}
+					}
+					// 重试失败，恢复原始响应体继续处理
+					resp.Body = io.NopCloser(bytes.NewReader(respBody))
+					break
+				}
+				// 不是thinking签名错误，恢复响应体
+				resp.Body = io.NopCloser(bytes.NewReader(respBody))
+			}
+		}
+
+		// 检查是否需要通用重试（排除400，因为400已经在上面特殊处理过了）
+		if resp.StatusCode >= 400 && resp.StatusCode != 400 && s.shouldRetryUpstreamError(account, resp.StatusCode) {
 			if attempt < maxRetries {
 				log.Printf("Account %d: upstream error %d, retry %d/%d after %v",
 					account.ID, resp.StatusCode, attempt, maxRetries, retryDelay)
@@ -1047,13 +1076,13 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 	}
 
 	// 处理错误响应（不可重试的错误）
-	if resp.StatusCode >= 400 {
-		// 可选：对部分 400 触发 failover（默认关闭以保持语义）
-		if resp.StatusCode == 400 && s.cfg != nil && s.cfg.Gateway.FailoverOn400 {
-			respBody, readErr := io.ReadAll(resp.Body)
-			if readErr != nil {
-				// ReadAll failed, fall back to normal error handling without consuming the stream
-				return s.handleErrorResponse(ctx, resp, c, account)
+		if resp.StatusCode >= 400 {
+			// 可选：对部分 400 触发 failover（默认关闭以保持语义）
+			if resp.StatusCode == 400 && s.cfg != nil && s.cfg.Gateway.FailoverOn400 {
+				respBody, readErr := io.ReadAll(io.LimitReader(resp.Body, 2<<20))
+				if readErr != nil {
+					// ReadAll failed, fall back to normal error handling without consuming the stream
+					return s.handleErrorResponse(ctx, resp, c, account)
 			}
 			_ = resp.Body.Close()
 			resp.Body = io.NopCloser(bytes.NewReader(respBody))
@@ -1110,7 +1139,7 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Context, account *Account, body []byte, token, tokenType, modelID string) (*http.Request, error) {
 	// 确定目标URL
 	targetURL := claudeAPIURL
-	if account.Type == AccountTypeAPIKey {
+	if account.Type == AccountTypeApiKey {
 		baseURL := account.GetBaseURL()
 		targetURL = baseURL + "/v1/messages"
 	}
@@ -1136,10 +1165,6 @@ func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Contex
 		}
 	}
 
-	// Filter thinking blocks from request body (prevents 400 errors from missing/invalid signatures).
-	// We apply this for the main /v1/messages path as well as count_tokens.
-	body = FilterThinkingBlocks(body)
-
 	req, err := http.NewRequestWithContext(ctx, "POST", targetURL, bytes.NewReader(body))
 	if err != nil {
 		return nil, err
@@ -1178,10 +1203,10 @@ func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Contex
 	// 处理anthropic-beta header（OAuth账号需要特殊处理）
 	if tokenType == "oauth" {
 		req.Header.Set("anthropic-beta", s.getBetaHeader(modelID, c.GetHeader("anthropic-beta")))
-	} else if s.cfg != nil && s.cfg.Gateway.InjectBetaForAPIKey && req.Header.Get("anthropic-beta") == "" {
+	} else if s.cfg != nil && s.cfg.Gateway.InjectBetaForApiKey && req.Header.Get("anthropic-beta") == "" {
 		// API-key：仅在请求显式使用 beta 特性且客户端未提供时，按需补齐（默认关闭）
 		if requestNeedsBetaFeatures(body) {
-			if beta := defaultAPIKeyBetaHeader(body); beta != "" {
+			if beta := defaultApiKeyBetaHeader(body); beta != "" {
 				req.Header.Set("anthropic-beta", beta)
 			}
 		}
@@ -1248,12 +1273,12 @@ func requestNeedsBetaFeatures(body []byte) bool {
 	return false
 }
 
-func defaultAPIKeyBetaHeader(body []byte) string {
+func defaultApiKeyBetaHeader(body []byte) string {
 	modelID := gjson.GetBytes(body, "model").String()
 	if strings.Contains(strings.ToLower(modelID), "haiku") {
-		return claude.APIKeyHaikuBetaHeader
+		return claude.ApiKeyHaikuBetaHeader
 	}
-	return claude.APIKeyBetaHeader
+	return claude.ApiKeyBetaHeader
 }
 
 func truncateForLog(b []byte, maxBytes int) string {
@@ -1270,6 +1295,20 @@ func truncateForLog(b []byte, maxBytes int) string {
 	return s
 }
 
+// isThinkingBlockSignatureError 检测是否是thinking block签名错误
+// 这类错误可以通过过滤thinking blocks并重试来解决
+func (s *GatewayService) isThinkingBlockSignatureError(respBody []byte) bool {
+	msg := strings.ToLower(strings.TrimSpace(extractUpstreamErrorMessage(respBody)))
+	if msg == "" {
+		return false
+	}
+
+	// 检测thinking block签名相关的错误
+	// 例如: "Invalid `signature` in `thinking` block"
+	return (strings.Contains(msg, "thinking") || strings.Contains(msg, "thought")) &&
+		strings.Contains(msg, "signature")
+}
+
 func (s *GatewayService) shouldFailoverOn400(respBody []byte) bool {
 	// 只对“可能是兼容性差异导致”的 400 允许切换，避免无意义重试。
 	// 默认保守：无法识别则不切换。
@@ -1318,7 +1357,13 @@ func (s *GatewayService) handleErrorResponse(ctx context.Context, resp *http.Res
 	body, _ := io.ReadAll(resp.Body)
 
 	// 处理上游错误，标记账号状态
-	s.rateLimitService.HandleUpstreamError(ctx, account, resp.StatusCode, resp.Header, body)
+	shouldDisable := false
+	if s.rateLimitService != nil {
+		shouldDisable = s.rateLimitService.HandleUpstreamError(ctx, account, resp.StatusCode, resp.Header, body)
+	}
+	if shouldDisable {
+		return nil, &UpstreamFailoverError{StatusCode: resp.StatusCode}
+	}
 
 	// 根据状态码返回适当的自定义错误响应（不透传上游详细信息）
 	var errType, errMsg string
@@ -1630,7 +1675,7 @@ func (s *GatewayService) replaceModelInResponseBody(body []byte, fromModel, toMo
 // RecordUsageInput 记录使用量的输入参数
 type RecordUsageInput struct {
 	Result       *ForwardResult
-	APIKey       *APIKey
+	ApiKey       *ApiKey
 	User         *User
 	Account      *Account
 	Subscription *UserSubscription // 可选：订阅信息
@@ -1639,7 +1684,7 @@ type RecordUsageInput struct {
 // RecordUsage 记录使用量并扣费（或更新订阅用量）
 func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInput) error {
 	result := input.Result
-	apiKey := input.APIKey
+	apiKey := input.ApiKey
 	user := input.User
 	account := input.Account
 	subscription := input.Subscription
@@ -1676,7 +1721,7 @@ func (s *GatewayService) RecordUsage(ctx context.Context, input *RecordUsageInpu
 	durationMs := int(result.Duration.Milliseconds())
 	usageLog := &UsageLog{
 		UserID:              user.ID,
-		APIKeyID:            apiKey.ID,
+		ApiKeyID:            apiKey.ID,
 		AccountID:           account.ID,
 		RequestID:           result.RequestID,
 		Model:               result.Model,
@@ -1754,15 +1799,14 @@ func (s *GatewayService) ForwardCountTokens(ctx context.Context, c *gin.Context,
 	body := parsed.Body
 	reqModel := parsed.Model
 
-	// Antigravity 账户不支持 count_tokens 转发，返回估算值
-	// 参考 Antigravity-Manager 和 proxycast 实现
+	// Antigravity 账户不支持 count_tokens 转发，直接返回空值
 	if account.Platform == PlatformAntigravity {
-		c.JSON(http.StatusOK, gin.H{"input_tokens": 100})
+		c.JSON(http.StatusOK, gin.H{"input_tokens": 0})
 		return nil
 	}
 
 	// 应用模型映射（仅对 apikey 类型账号）
-	if account.Type == AccountTypeAPIKey {
+	if account.Type == AccountTypeApiKey {
 		if reqModel != "" {
 			mappedModel := account.GetMappedModel(reqModel)
 			if mappedModel != reqModel {
@@ -1848,7 +1892,7 @@ func (s *GatewayService) ForwardCountTokens(ctx context.Context, c *gin.Context,
 func (s *GatewayService) buildCountTokensRequest(ctx context.Context, c *gin.Context, account *Account, body []byte, token, tokenType, modelID string) (*http.Request, error) {
 	// 确定目标 URL
 	targetURL := claudeAPICountTokensURL
-	if account.Type == AccountTypeAPIKey {
+	if account.Type == AccountTypeApiKey {
 		baseURL := account.GetBaseURL()
 		targetURL = baseURL + "/v1/messages/count_tokens"
 	}
@@ -1866,9 +1910,6 @@ func (s *GatewayService) buildCountTokensRequest(ctx context.Context, c *gin.Con
 		}
 	}
 
-	// Filter thinking blocks from request body (prevents 400 errors from invalid signatures)
-	body = FilterThinkingBlocks(body)
-
 	req, err := http.NewRequestWithContext(ctx, "POST", targetURL, bytes.NewReader(body))
 	if err != nil {
 		return nil, err
@@ -1910,10 +1951,10 @@ func (s *GatewayService) buildCountTokensRequest(ctx context.Context, c *gin.Con
 	// OAuth 账号：处理 anthropic-beta header
 	if tokenType == "oauth" {
 		req.Header.Set("anthropic-beta", s.getBetaHeader(modelID, c.GetHeader("anthropic-beta")))
-	} else if s.cfg != nil && s.cfg.Gateway.InjectBetaForAPIKey && req.Header.Get("anthropic-beta") == "" {
+	} else if s.cfg != nil && s.cfg.Gateway.InjectBetaForApiKey && req.Header.Get("anthropic-beta") == "" {
 		// API-key：与 messages 同步的按需 beta 注入（默认关闭）
 		if requestNeedsBetaFeatures(body) {
-			if beta := defaultAPIKeyBetaHeader(body); beta != "" {
+			if beta := defaultApiKeyBetaHeader(body); beta != "" {
 				req.Header.Set("anthropic-beta", beta)
 			}
 		}