fix: make error passthrough effective for non-failover upstream errors

backend/internal/service/gateway_service.go

@@ -3563,6 +3563,34 @@ func (s *GatewayService) handleErrorResponse(ctx context.Context, resp *http.Res
 		)
 	}
 
+	// 非 failover 错误也支持错误透传规则匹配。
+	if status, errType, errMsg, matched := applyErrorPassthroughRule(
+		c,
+		account.Platform,
+		resp.StatusCode,
+		body,
+		http.StatusBadGateway,
+		"upstream_error",
+		"Upstream request failed",
+	); matched {
+		c.JSON(status, gin.H{
+			"type": "error",
+			"error": gin.H{
+				"type":    errType,
+				"message": errMsg,
+			},
+		})
+
+		summary := upstreamMsg
+		if summary == "" {
+			summary = errMsg
+		}
+		if summary == "" {
+			return nil, fmt.Errorf("upstream error: %d (passthrough rule matched)", resp.StatusCode)
+		}
+		return nil, fmt.Errorf("upstream error: %d (passthrough rule matched) message=%s", resp.StatusCode, summary)
+	}
+
 	// 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
 	var statusCode int
@@ -3694,6 +3722,33 @@ func (s *GatewayService) handleRetryExhaustedError(ctx context.Context, resp *ht
 		)
 	}
 
+	if status, errType, errMsg, matched := applyErrorPassthroughRule(
+		c,
+		account.Platform,
+		resp.StatusCode,
+		respBody,
+		http.StatusBadGateway,
+		"upstream_error",
+		"Upstream request failed after retries",
+	); matched {
+		c.JSON(status, gin.H{
+			"type": "error",
+			"error": gin.H{
+				"type":    errType,
+				"message": errMsg,
+			},
+		})
+
+		summary := upstreamMsg
+		if summary == "" {
+			summary = errMsg
+		}
+		if summary == "" {
+			return nil, fmt.Errorf("upstream error: %d (retries exhausted, passthrough rule matched)", resp.StatusCode)
+		}
+		return nil, fmt.Errorf("upstream error: %d (retries exhausted, passthrough rule matched) message=%s", resp.StatusCode, summary)
+	}
+
 	// 返回统一的重试耗尽错误响应
 	c.JSON(http.StatusBadGateway, gin.H{
 		"type": "error",