fix(mediaserver): 翻页中途失败不再被当成查询结束

新增的关键字翻页逻辑只在第一页失败时返回 None，后续页面请求失败会让生成器
正常结束：get_movies 返回残缺列表、按标题定位剧集返回空串，等于把「连不上」
误报成「确定不在库中」，可能触发重复下载。

改为中途失败抛出私有异常并由调用方转成 None，恢复「连接失败返回 None、
未找到返回空结果」的区分；补 2 条回归，均已确认在修正前失败。

app/modules/mediavault/mediavault.py

@@ -14,6 +14,14 @@ from app.schemas.mediaserver import RefreshMediaItem as _SchemaRefreshMediaItem
 from app.schemas.types import MediaSource, MediaType
 
 
+class _SearchInterrupted(Exception):
+    """关键字翻页中途请求失败。
+
+    与「查完了」区分开：调用方据此返回 None（服务不可达），而不是空结果
+    （确定不在库中）——后者会让上层误判成需要重新下载。
+    """
+
+
 class MediaVault:
     """MediaVault 自建媒体库客户端。
 
@@ -234,17 +242,20 @@ class MediaVault:
             return None
 
         def rows() -> Generator[Dict[str, Any], Any, None]:
-            result: Optional[Dict[str, Any]] = first
+            result: Dict[str, Any] = first
             page = 1
-            while result is not None:
+            while True:
                 batch = result.get("items") or []
                 yield from batch
                 if len(batch) < self.PAGE_LIMIT:
                     return
                 page += 1
-                result = self.__query_items(
+                following = self.__query_items(
                     keyword=keyword, kinds=kinds, page=page, page_size=self.PAGE_LIMIT
                 )
+                if following is None:
+                    raise _SearchInterrupted
+                result = following
 
         return rows()
 
@@ -273,7 +284,11 @@ class MediaVault:
         if rows is None:
             return None
         movies = []
-        for row in rows:
+        try:
+            search_rows = list(rows)
+        except _SearchInterrupted:
+            return None
+        for row in search_rows:
             item = self.__format_item_info(row)
             if not item or item.title != title:
                 continue
@@ -339,7 +354,11 @@ class MediaVault:
         rows = self.__search_rows(keyword=title, kinds="Series")
         if rows is None:
             return None
-        for row in rows:
+        try:
+            search_rows = list(rows)
+        except _SearchInterrupted:
+            return None
+        for row in search_rows:
             item = self.__format_item_info(row)
             if not item or item.title != title:
                 continue

tests/test_mediavault_module.py

@@ -531,3 +531,33 @@ def test_play_item_and_backdrop_images_carry_no_credentials():
 
     assert urls
     assert all("api_key" not in url for url in urls)
+
+
+def _failing_second_page(total_rows: list):
+    """第一页正常、后续页请求失败，模拟翻页中途断连。"""
+    calls = {"n": 0}
+
+    def handler(params, _data):
+        calls["n"] += 1
+        if calls["n"] > 1:
+            return None
+        size = int(params.get("page_size", 40))
+        return Result(True, {"items": total_rows[:size], "total": len(total_rows)})
+
+    return handler
+
+
+def test_get_movies_reports_unreachable_when_a_later_page_fails():
+    """翻页中途断连必须返回 None，不能把残缺结果当成「不在库中」。"""
+    rows = [_item_row(i, title=f"沙丘{i}") for i in range(MediaVault.PAGE_LIMIT)]
+    client = _client({"/items": _failing_second_page(rows)})
+
+    assert client.get_movies(title="沙丘") is None
+
+
+def test_find_series_reports_unreachable_when_a_later_page_fails():
+    """同上：剧集定位不能把断连误判成整部剧未入库。"""
+    rows = [_item_row(i, kind="Series", title=f"剧{i}") for i in range(MediaVault.PAGE_LIMIT)]
+    client = _client({"/items": _failing_second_page(rows)})
+
+    assert client.get_tv_episodes(title="剧A") == (None, None)