fix: restore non-failover error passthrough from 7b156489

backend/internal/service/error_passthrough_runtime.go

@@ -0,0 +1,67 @@
+package service
+
+import "github.com/gin-gonic/gin"
+
+const errorPassthroughServiceContextKey = "error_passthrough_service"
+
+// BindErrorPassthroughService 将错误透传服务绑定到请求上下文，供 service 层在非 failover 场景下复用规则。
+func BindErrorPassthroughService(c *gin.Context, svc *ErrorPassthroughService) {
+	if c == nil || svc == nil {
+		return
+	}
+	c.Set(errorPassthroughServiceContextKey, svc)
+}
+
+func getBoundErrorPassthroughService(c *gin.Context) *ErrorPassthroughService {
+	if c == nil {
+		return nil
+	}
+	v, ok := c.Get(errorPassthroughServiceContextKey)
+	if !ok {
+		return nil
+	}
+	svc, ok := v.(*ErrorPassthroughService)
+	if !ok {
+		return nil
+	}
+	return svc
+}
+
+// applyErrorPassthroughRule 按规则改写错误响应；未命中时返回默认响应参数。
+func applyErrorPassthroughRule(
+	c *gin.Context,
+	platform string,
+	upstreamStatus int,
+	responseBody []byte,
+	defaultStatus int,
+	defaultErrType string,
+	defaultErrMsg string,
+) (status int, errType string, errMsg string, matched bool) {
+	status = defaultStatus
+	errType = defaultErrType
+	errMsg = defaultErrMsg
+
+	svc := getBoundErrorPassthroughService(c)
+	if svc == nil {
+		return status, errType, errMsg, false
+	}
+
+	rule := svc.MatchRule(platform, upstreamStatus, responseBody)
+	if rule == nil {
+		return status, errType, errMsg, false
+	}
+
+	status = upstreamStatus
+	if !rule.PassthroughCode && rule.ResponseCode != nil {
+		status = *rule.ResponseCode
+	}
+
+	errMsg = ExtractUpstreamErrorMessage(responseBody)
+	if !rule.PassthroughBody && rule.CustomMessage != nil {
+		errMsg = *rule.CustomMessage
+	}
+
+	// 与现有 failover 场景保持一致：命中规则时统一返回 upstream_error。
+	errType = "upstream_error"
+	return status, errType, errMsg, true
+}