diff --git a/backend/internal/service/antigravity_gateway_service.go b/backend/internal/service/antigravity_gateway_service.go
index a66a1df8..468d94c7 100644
--- a/backend/internal/service/antigravity_gateway_service.go
+++ b/backend/internal/service/antigravity_gateway_service.go
@@ -779,128 +779,6 @@ func (s *AntigravityGatewayService) Forward(ctx context.Context, c *gin.Context,
 	if resp.StatusCode >= 400 {
 		respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 2<<20))
 
-		// 优先检测 thinking block 的 signature 相关错误（400）并重试一次：
-		// Antigravity /v1internal 链路在部分场景会对 thought/thinking signature 做严格校验，
-		// 当历史消息携带的 signature 不合法时会直接 400；去除 thinking 后可继续完成请求。
-		if resp.StatusCode == http.StatusBadRequest && isSignatureRelatedError(respBody) {
-			upstreamMsg := strings.TrimSpace(extractAntigravityErrorMessage(respBody))
-			upstreamMsg = sanitizeUpstreamErrorMessage(upstreamMsg)
-			logBody := s.settingService != nil && s.settingService.cfg != nil && s.settingService.cfg.Gateway.LogUpstreamErrorBody
-			maxBytes := 2048
-			if s.settingService != nil && s.settingService.cfg != nil && s.settingService.cfg.Gateway.LogUpstreamErrorBodyMaxBytes > 0 {
-				maxBytes = s.settingService.cfg.Gateway.LogUpstreamErrorBodyMaxBytes
-			}
-			upstreamDetail := ""
-			if logBody {
-				upstreamDetail = truncateString(string(respBody), maxBytes)
-			}
-			appendOpsUpstreamError(c, OpsUpstreamErrorEvent{
-				Platform:           account.Platform,
-				AccountID:          account.ID,
-				AccountName:        account.Name,
-				UpstreamStatusCode: resp.StatusCode,
-				UpstreamRequestID:  resp.Header.Get("x-request-id"),
-				Kind:               "signature_error",
-				Message:            upstreamMsg,
-				Detail:             upstreamDetail,
-			})
-
-			// Conservative two-stage fallback:
-			// 1) Disable top-level thinking + thinking->text
-			// 2) Only if still signature-related 400: also downgrade tool_use/tool_result to text.
-
-			retryStages := []struct {
-				name  string
-				strip func(*antigravity.ClaudeRequest) (bool, error)
-			}{
-				{name: "thinking-only", strip: stripThinkingFromClaudeRequest},
-				{name: "thinking+tools", strip: stripSignatureSensitiveBlocksFromClaudeRequest},
-			}
-
-			for _, stage := range retryStages {
-				retryClaudeReq := claudeReq
-				retryClaudeReq.Messages = append([]antigravity.ClaudeMessage(nil), claudeReq.Messages...)
-
-				stripped, stripErr := stage.strip(&retryClaudeReq)
-				if stripErr != nil || !stripped {
-					continue
-				}
-
-				log.Printf("Antigravity account %d: detected signature-related 400, retrying once (%s)", account.ID, stage.name)
-
-				retryGeminiBody, txErr := antigravity.TransformClaudeToGeminiWithOptions(&retryClaudeReq, projectID, mappedModel, s.getClaudeTransformOptions(ctx))
-				if txErr != nil {
-					continue
-				}
-				retryReq, buildErr := antigravity.NewAPIRequest(ctx, action, accessToken, retryGeminiBody)
-				if buildErr != nil {
-					continue
-				}
-				retryResp, retryErr := s.httpUpstream.Do(retryReq, proxyURL, account.ID, account.Concurrency)
-				if retryErr != nil {
-					appendOpsUpstreamError(c, OpsUpstreamErrorEvent{
-						Platform:           account.Platform,
-						AccountID:          account.ID,
-						AccountName:        account.Name,
-						UpstreamStatusCode: 0,
-						Kind:               "signature_retry_request_error",
-						Message:            sanitizeUpstreamErrorMessage(retryErr.Error()),
-					})
-					log.Printf("Antigravity account %d: signature retry request failed (%s): %v", account.ID, stage.name, retryErr)
-					continue
-				}
-
-				if retryResp.StatusCode < 400 {
-					_ = resp.Body.Close()
-					resp = retryResp
-					respBody = nil
-					break
-				}
-
-				retryBody, _ := io.ReadAll(io.LimitReader(retryResp.Body, 2<<20))
-				_ = retryResp.Body.Close()
-				kind := "signature_retry"
-				if strings.TrimSpace(stage.name) != "" {
-					kind = "signature_retry_" + strings.ReplaceAll(stage.name, "+", "_")
-				}
-				retryUpstreamMsg := strings.TrimSpace(extractAntigravityErrorMessage(retryBody))
-				retryUpstreamMsg = sanitizeUpstreamErrorMessage(retryUpstreamMsg)
-				retryUpstreamDetail := ""
-				if logBody {
-					retryUpstreamDetail = truncateString(string(retryBody), maxBytes)
-				}
-				appendOpsUpstreamError(c, OpsUpstreamErrorEvent{
-					Platform:           account.Platform,
-					AccountID:          account.ID,
-					AccountName:        account.Name,
-					UpstreamStatusCode: retryResp.StatusCode,
-					UpstreamRequestID:  retryResp.Header.Get("x-request-id"),
-					Kind:               kind,
-					Message:            retryUpstreamMsg,
-					Detail:             retryUpstreamDetail,
-				})
-
-				// If this stage fixed the signature issue, we stop; otherwise we may try the next stage.
-				if retryResp.StatusCode != http.StatusBadRequest || !isSignatureRelatedError(retryBody) {
-					respBody = retryBody
-					resp = &http.Response{
-						StatusCode: retryResp.StatusCode,
-						Header:     retryResp.Header.Clone(),
-						Body:       io.NopCloser(bytes.NewReader(retryBody)),
-					}
-					break
-				}
-
-				// Still signature-related; capture context and allow next stage.
-				respBody = retryBody
-				resp = &http.Response{
-					StatusCode: retryResp.StatusCode,
-					Header:     retryResp.Header.Clone(),
-					Body:       io.NopCloser(bytes.NewReader(retryBody)),
-				}
-			}
-		}
-
 		// 处理错误响应（重试后仍失败或不触发重试）
 		if resp.StatusCode >= 400 {
 			s.handleUpstreamError(ctx, prefix, account, resp.StatusCode, resp.Header, respBody, quotaScope)