fix(clothes): 保护失败原因并可靠回退额度

仅属主可查看失败原因，分享只读场景置空；额度回退改用独立
ctx，避免客户端断开导致回退失败；新增 ImageProcessStatus 与
FailReason 响应字段，并抽取 detachedCtx 复用后台任务上下文。

internal/service/clothes.go

@@ -103,7 +103,7 @@ func (s *ClothesService) Upload(ctx context.Context, userID int64, fileHeader *m
 	originalPath, serr := upload.FileSaveTmpBytes(ctx, imageData, originalName, fmt.Sprintf("pending/%d", userID))
 	if serr != nil {
 		slog.ErrorContext(ctx, "clothes upload: save original image failed", "user_id", userID, "error", serr)
-		refundCosQuota(ctx, userID, 1, 0, "原图持久化失败回退")
+		refundUploadQuotaOnFail(ctx, userID, "原图持久化失败回退")
 		return nil, errcode.UploadFileSaveFailed
 	}
 	clothes := &mysqlmodel.Clothes{
@@ -117,8 +117,8 @@ func (s *ClothesService) Upload(ctx context.Context, userID int64, fileHeader *m
 		slog.ErrorContext(ctx, "clothes upload: create clothes record failed",
 			"user_id", userID, "clothes_uuid", clothesUUID, "error", err)
 		_ = os.Remove(originalPath)
-		// 建记录失败，回退已扣额度。
-		refundCosQuota(ctx, userID, 1, 0, "上传失败回退")
+		// 建记录失败，回退已扣额度（独立 ctx：客户端中途断开也要保证退回）。
+		refundUploadQuotaOnFail(ctx, userID, "上传失败回退")
 		return nil, errcode.ClothesCreateFailed
 	}
 
@@ -133,6 +133,23 @@ func (s *ClothesService) Upload(ctx context.Context, userID int64, fileHeader *m
 	}, nil
 }
 
+// detachedCtx 基于 Background 派生独立 ctx：继承 trace 链路但切断请求取消信号，
+// 供「与客户端连接解耦」的后台任务与「必须完成」的收尾操作使用。
+func detachedCtx(parent context.Context, timeout time.Duration) (context.Context, context.CancelFunc) {
+	return context.WithTimeout(
+		trace.ContextWithSpanContext(context.Background(), trace.SpanContextFromContext(parent)),
+		timeout,
+	)
+}
+
+// refundUploadQuotaOnFail 用不受请求取消影响的 ctx 回退上传额度：
+// 客户端中途断开导致请求 ctx 已取消时，仍要保证额度退回成功。
+func refundUploadQuotaOnFail(parent context.Context, userID int64, reason string) {
+	ctx, cancel := detachedCtx(parent, 30*time.Second)
+	defer cancel()
+	refundCosQuota(ctx, userID, 1, 0, reason)
+}
+
 // processImageAsync 后台执行抠图、上传 COS、分类，并回填衣物记录。
 func (s *ClothesService) processImageAsync(parentCtx context.Context, userID int64, clothesUUID string, imageData []byte, originalPath string) {
 	// 限流：获取信号量，超出并发上限时阻塞等待。
@@ -140,7 +157,7 @@ func (s *ClothesService) processImageAsync(parentCtx context.Context, userID int
 	defer func() { <-imageProcessSem }()
 
 	// 派生独立 ctx：继承父 trace 信息，但切断取消信号，避免复用已结束的请求 ctx。
-	ctx, cancel := context.WithTimeout(trace.ContextWithSpanContext(context.Background(), trace.SpanContextFromContext(parentCtx)), 3*time.Minute)
+	ctx, cancel := detachedCtx(parentCtx, 3*time.Minute)
 	defer cancel()
 
 	ctx, span := global.Tracer.Start(ctx, "svc.ClothesProcessImageAsync")
@@ -392,6 +409,10 @@ func (s *ClothesService) GetByUUID(ctx context.Context, userID int64, request *d
 		}
 	}
 	response := buildClothesResponse(clothes)
+	// 非属主只读查看（穿搭分享）：不暴露内部失败原因
+	if clothes.UserID != userID {
+		response.FailReason = ""
+	}
 	return &response, nil
 }
 
@@ -610,6 +631,9 @@ func buildClothesResponse(c *mysqlmodel.Clothes) dto.ClothesGetByUUIDResponse {
 		Name:           c.Name,
 		Remark:         c.Remark,
 		ProcessedImage: processed,
+
+		ImageProcessStatus: c.ImageProcessStatus,
+		FailReason:         c.FailReason,
 	}
 }