fix(4.0): 更新规则时先在所有实例上匹配种子，任一实例不可用则不做任何修改

此前逐实例移动种子，后面的实例不可用时前面的实例已经移动，数据库仍记着旧目录。

backend/src/module/manager/torrent.py

@@ -221,13 +221,33 @@ class TorrentManager:
             # 没换：规则的种子可能经订阅进了别的实例，逐个实例按各自的
             # 下载目录移动
             if new_instance == old_instance:
-                for instance_id in await self._torrent_instances(old_data):
-                    root = settings.downloader_instance(instance_id).path
-                    moved_path = gen_save_path(data, root)
-                    old_paths = _save_paths(old_data, root)
-                    if old_paths == {normalize_save_path(moved_path)}:
-                        continue
-                    match_list = await self.__match_torrents_list(old_data, instance_id)
+                # 先在所有实例上匹配种子：任一实例不可用就什么都不改，
+                # 避免一部分实例已移动而规则仍记着旧目录
+                moves = []
+                try:
+                    for instance_id in await self._torrent_instances(old_data):
+                        root = settings.downloader_instance(instance_id).path
+                        moved_path = gen_save_path(data, root)
+                        old_paths = _save_paths(old_data, root)
+                        if old_paths == {normalize_save_path(moved_path)}:
+                            continue
+                        match_list = await self.__match_torrents_list(
+                            old_data, instance_id
+                        )
+                        moves.append((instance_id, moved_path, old_paths, match_list))
+                except ConnectionError as e:
+                    logger.warning(
+                        "[Manager] Can't update rule %s: %s", old_data.rule_name, e
+                    )
+                    return ResponseModel(
+                        status_code=500,
+                        status=False,
+                        msg_en=f"Updating {old_data.official_title} failed: a "
+                        "downloader is unreachable; nothing was changed, retry later.",
+                        msg_zh=f"更新 {old_data.official_title} 失败：下载器不可用，"
+                        "规则未修改，请稍后重试。",
+                    )
+                for instance_id, moved_path, old_paths, match_list in moves:
                     async with DownloadClient(instance_id) as client:
                         # Move existing torrents to new location if path changed
                         if match_list:

backend/src/test/test_multi_downloader.py

@@ -448,6 +448,44 @@ class TestRuleOnAnotherInstance:
         moved = _mock("b")._torrents["hb"]["save_path"]
         assert moved == "/b/Bangumi/Test Anime (2024)/Season 2"
 
+    async def test_update_rule_unavailable_instance_changes_nothing_for_retry(
+        self, two_instances
+    ):
+        """实例 b 不可用：a 上的种子不移动、规则不改，b 恢复后重试两边一起移动。"""
+        from module.manager import TorrentManager
+        from module.models import BangumiUpdate
+
+        bangumi_id = await self._rule_with_torrent_on_a()
+        hb = _completed("B", "hb", "/b/Bangumi/Test Anime (2024)/Season 1")
+        _mock("b")._torrents["hb"] = hb
+        _mock("b").auth = AsyncMock(return_value=False)  # type: ignore[method-assign]
+        async with Database() as db:
+            await db.torrent.add(
+                Torrent(name="B", url="u-b", bangumi_id=1, downloader_id="b")
+            )
+            old = await db.bangumi.search_id(bangumi_id)
+            assert old is not None
+            update = BangumiUpdate(**old.model_dump(exclude={"id"}))
+            update.season = 2
+            resp = await TorrentManager(db).update_rule(bangumi_id, update)
+            assert resp.status is False and resp.status_code == 500
+            assert _mock("a")._torrents["old"]["save_path"] == old.save_path
+            kept = await db.bangumi.search_id(bangumi_id)
+            assert kept is not None and kept.save_path == old.save_path
+
+            # 登录失败会丢弃缓存的客户端，恢复后是新的客户端实例
+            _mock("b")._torrents["hb"] = hb
+            update = BangumiUpdate(**old.model_dump(exclude={"id"}))
+            update.season = 2
+            retry = await TorrentManager(db).update_rule(bangumi_id, update)
+            assert retry.status is True
+            new = await db.bangumi.search_id(bangumi_id)
+
+        season2 = "Bangumi/Test Anime (2024)/Season 2"
+        assert new is not None and new.save_path == f"/a/{season2}"
+        assert _mock("a")._torrents["old"]["save_path"] == f"/a/{season2}"
+        assert _mock("b")._torrents["hb"]["save_path"] == f"/b/{season2}"
+
     async def test_delete_rule_unavailable_instance_keeps_rule_for_retry(
         self, two_instances
     ):