Fix: while placeholder file got conflict, original file might be deleted

pkg/filesystem/upload.go

@@ -178,7 +178,7 @@ func (fs *FileSystem) CreateUploadSession(ctx context.Context, file *fsctx.FileS
 		fs.Use("AfterUpload", HookClearFileHeaderSize)
 	}
 
-	fs.Use("AfterUpload", GenericAfterUpload)
+	// 验证文件规格
 	if err := fs.Upload(ctx, file); err != nil {
 		return nil, err
 	}
@@ -201,6 +201,12 @@ func (fs *FileSystem) CreateUploadSession(ctx context.Context, file *fsctx.FileS
 		return nil, err
 	}
 
+	// 创建占位符
+	fs.Use("AfterUpload", GenericAfterUpload)
+	if err := fs.Upload(ctx, file); err != nil {
+		return nil, err
+	}
+
 	// 创建回调会话
 	err = cache.Set(
 		UploadSessionCachePrefix+callbackKey,