fix(transfer): continue overwrite after target cleanup

## 问题

覆盖裁决确认旧媒体库目标存在后，洗版流程可能在实际备份前删除旧目标。恢复整理时备份步骤把旧目标和备份都不存在视为未知冲突，任务进入人工复核，暂存的新版本无法入库。

## 修复

- 备份步骤在确认旧目标已被外部删除、且备份目标也不存在时记录为无副作用跳过。
- 继续提升已完整暂存的新版本；移动整理仍在提升成功后清理源文件。
- 查询失败、两端同时存在或存在备份但状态矛盾时继续保持人工复核保护。
- 增加持久整理回归测试，覆盖覆盖裁决后旧目标被删除的场景。

## 验证

- `tests/test_transfer_safe_overwrite.py`：94 passed
- 整理执行、持久化、人工复核、提交、worker、计划测试：202 passed
- changed-file Pylint：10.00/10

Fixes #7120

app/modules/filemanager/transhandler.py

@@ -1211,11 +1211,13 @@ class TransHandler:
             target: Path,
             kind: str,
             expected_source: Optional[FileItem] = None,
-    ) -> FileItem:
+            allow_missing_source: bool = False,
+    ) -> Optional[FileItem]:
         """
         执行同目录无覆盖重命名，并用两端严格查询恢复中断操作。
 
-        两端同时存在或同时消失视为冲突；查询或身份无法确认时不自动重放。
+        两端同时存在或遗留步骤中同时消失视为冲突；只有覆盖备份在执行前明确
+        发现旧目标缺失时，才记录为无副作用的跳过。查询或身份无法确认时不自动重放。
 
         :param step_runner: 步骤执行器；None 时同步执行
         :param storage_oper: 负责查询和重命名的存储适配器
@@ -1224,14 +1226,18 @@ class TransHandler:
         :param target: 新路径，必须不存在且由调用方保持在同一目录
         :param kind: 步骤操作类别
         :param expected_source: 可选的冻结源身份；提供时在操作前后核对
-        :return: 重命名后的文件项
+        :param allow_missing_source: 旧目标已被外部删除时是否将重命名记录为跳过
+        :return: 重命名后的文件项；允许旧目标缺失并跳过时返回 None
         """
         def execute() -> TransferStepResult:
             """
             目标必须不存在，避免适配器的 rename 意外替换其它文件。
             """
             source_item = storage_oper.get_item_strict(source)
-            if source_item is None or storage_oper.get_item_strict(target) is not None:
+            target_item = storage_oper.get_item_strict(target)
+            if allow_missing_source and source_item is None and target_item is None:
+                return TransferStepResult(payload={"item": None, "skipped": True})
+            if source_item is None or target_item is not None:
                 raise RuntimeError(f"重命名路径状态冲突：{source} -> {target}")
             if expected_source is not None:
                 cls.__assert_file_identity(expected_source, source_item)
@@ -1285,7 +1291,9 @@ class TransHandler:
             execute=execute, observe=observe,
         )
         item = cls.__restore_step_item(renamed)
-        if item is None:
+        if item is None and not (
+                allow_missing_source and renamed.payload.get("skipped") is True
+        ):
             raise RuntimeError("重命名成功证据缺少目标文件")
         return item
 
@@ -1339,12 +1347,13 @@ class TransHandler:
             step_runner=step_runner, storage_oper=target_oper,
             storage=target_storage, source=target_file, target=backup,
             kind="backup_overwrite_target",
+            allow_missing_source=True,
         )
-        new_item = cls.__rename_with_step(
+        new_item = cast(FileItem, cls.__rename_with_step(
             step_runner=step_runner, storage_oper=target_oper,
             storage=target_storage, source=stage, target=target_file,
             kind="promote_overwrite_target", expected_source=new_item,
-        )
+        ))
 
         def confirm_replacement() -> None:
             """

tests/test_transfer_safe_overwrite.py

@@ -498,6 +498,48 @@ def test_safe_overwrite_preserves_transfer_modes(tmp_path, monkeypatch, transfer
     assert target.is_symlink() is (transfer_type == "softlink")
 
 
+def test_overwrite_promotes_new_target_when_old_target_disappears_before_backup(
+        tmp_path, monkeypatch, repository_factory,
+):
+    """
+    持久覆盖裁决后旧目标被洗版清理时，跳过无效备份并继续提升新文件。
+    """
+    source = tmp_path / "download.mkv"
+    target = tmp_path / "Movie.2026.mkv"
+    source.write_bytes(b"new-version")
+    target.write_bytes(b"old-version")
+    checkpoint = _checkpoint(source, target, transfer_type="move")
+    repository = repository_factory(checkpoint)
+    real_get_item_strict = LocalStorage.get_item_strict
+    deleted = False
+
+    def remove_target_after_decision(self, path):
+        """
+        模拟覆盖裁决完成后洗版流程删除媒体库旧目标。
+        """
+        nonlocal deleted
+        item = real_get_item_strict(self, path)
+        if path == target and item is not None and not deleted:
+            target.unlink()
+            deleted = True
+        return item
+
+    monkeypatch.setattr(LocalStorage, "get_item_strict", remove_target_after_decision)
+    result = _execute(checkpoint, monkeypatch, _durable_runner(repository, checkpoint))
+
+    assert result.success
+    assert target.read_bytes() == b"new-version"
+    assert not source.exists()
+    assert not list(tmp_path.glob(".mp-*"))
+    backup_step = next(
+        step for step in repository.get_snapshot(task_id="safe-overwrite").steps
+        if step.kind == "backup_overwrite_target"
+    )
+    assert backup_step.state is TransferStepState.SUCCEEDED
+    assert backup_step.result is not None
+    assert backup_step.result.payload["skipped"] is True
+
+
 @pytest.fixture
 def repository_factory():
     """