feat(transfer): 新增 TransferOverwriteCheck 事件支持插件介入覆盖判断

允许插件在覆盖模式判断前提供目标文件的真实大小或直接给出覆盖决策，
解决 .strm 等本地大小不准的场景下 size 模式失效的问题。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/filemanager/transhandler.py

@@ -19,6 +19,7 @@ from app.schemas import (
     TransferDirectoryConf,
     FileItem,
     TransferInterceptEventData,
+    TransferOverwriteCheckEventData,
     TransferRenameEventData,
 )
 from app.schemas.types import MediaType, ChainEventType
@@ -297,12 +298,63 @@ class TransHandler:
                             logger.info(
                                 f"目的文件系统中已经存在同名文件 {target_file}，当前整理覆盖模式设置为 {overwrite_mode}"
                             )
-                            if overwrite_mode == "always":
+                            # 触发覆盖检查事件，允许插件提供目标文件真实大小
+                            # 或直接给出覆盖决策（例如 .strm 文件指向网盘原始文件）
+                            overwrite_event_data = TransferOverwriteCheckEventData(
+                                fileitem=fileitem,
+                                target_item=target_item,
+                                target_storage=target_storage,
+                                target_path=new_file,
+                                overwrite_mode=overwrite_mode or "",
+                                transfer_type=transfer_type,
+                            )
+                            overwrite_event = eventmanager.send_event(
+                                ChainEventType.TransferOverwriteCheck,
+                                overwrite_event_data,
+                            )
+                            plugin_overwrite: Optional[bool] = None
+                            plugin_target_size: Optional[int] = None
+                            if overwrite_event and overwrite_event.event_data:
+                                overwrite_event_data = overwrite_event.event_data
+                                plugin_overwrite = overwrite_event_data.overwrite
+                                plugin_target_size = overwrite_event_data.target_size
+                                if (
+                                    plugin_overwrite is not None
+                                    or plugin_target_size is not None
+                                ):
+                                    logger.info(
+                                        f"覆盖检查事件由 {overwrite_event_data.source} 处理："
+                                        f"overwrite={plugin_overwrite}, "
+                                        f"target_size={plugin_target_size}, "
+                                        f"reason={overwrite_event_data.reason}"
+                                    )
+                            if plugin_overwrite is True:
+                                overflag = True
+                            elif plugin_overwrite is False:
+                                self.__update_result(
+                                    result=result,
+                                    success=False,
+                                    message=overwrite_event_data.reason
+                                    or "插件决定不覆盖已有文件",
+                                    fileitem=fileitem,
+                                    target_item=target_item,
+                                    target_diritem=target_diritem,
+                                    fail_list=[fileitem.path],
+                                    transfer_type=transfer_type,
+                                    need_notify=need_notify,
+                                )
+                                return result
+                            elif overwrite_mode == "always":
                                 # 总是覆盖同名文件
                                 overflag = True
                             elif overwrite_mode == "size":
                                 # 存在时大覆盖小
-                                if target_item.size < fileitem.size:
+                                target_size = (
+                                    plugin_target_size
+                                    if plugin_target_size is not None
+                                    else target_item.size
+                                )
+                                if target_size < fileitem.size:
                                     logger.info(
                                         f"目标文件文件大小更小，将覆盖：{new_file}"
                                     )