fix: 补齐 failover 路径的 appendOpsUpstreamError 日志

审查发现 error 路径缺少 appendOpsUpstreamError 和 upstreamDetail
记录，与 forwardResponsesViaRawChatCompletions 不对称。

backend/internal/service/openai_gateway_messages_chat_fallback.go

@@ -154,8 +154,27 @@ func (s *OpenAIGatewayService) forwardAnthropicViaRawChatCompletions(
 		_ = resp.Body.Close()
 		resp.Body = io.NopCloser(bytes.NewReader(respBody))
 
-		upstreamMsg := sanitizeUpstreamErrorMessage(strings.TrimSpace(extractUpstreamErrorMessage(respBody)))
+		upstreamMsg := strings.TrimSpace(extractUpstreamErrorMessage(respBody))
+		upstreamMsg = sanitizeUpstreamErrorMessage(upstreamMsg)
 		if s.shouldFailoverOpenAIUpstreamResponse(resp.StatusCode, upstreamMsg, respBody) {
+			upstreamDetail := ""
+			if s.cfg != nil && s.cfg.Gateway.LogUpstreamErrorBody {
+				maxBytes := s.cfg.Gateway.LogUpstreamErrorBodyMaxBytes
+				if maxBytes <= 0 {
+					maxBytes = 2048
+				}
+				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:               "failover",
+				Message:            upstreamMsg,
+				Detail:             upstreamDetail,
+			})
 			s.handleOpenAIAccountUpstreamError(ctx, account, resp.StatusCode, resp.Header, respBody, upstreamModel)
 			return nil, &UpstreamFailoverError{
 				StatusCode:             resp.StatusCode,