fix: 网络断开后任务永久卡在"下载中"

三处协同修复：
1) worker 异常分支补 _release_stuck_task，
   标记 FailedDownload、推进 finish_task、清残留。
2) download_media 中 fetch_message 加 try-except，
   连接异常返回 FailedDownload，不再让异常冒泡。
3) download_chat_task 用 try/finally 兜底回写
   chat_download_config.total_task，避免 _wait_node_finish
   误判频道已完成而切到下一个。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

media_downloader.py

@@ -423,7 +423,15 @@ async def download_media(
     task_start_time: float = time.time()
     media_size = 0
     _media = None
-    message = await fetch_message(client, message)
+    # 关键修复：fetch_message 是发起任何下载前的网络调用，连接异常时不能让异常一路冒泡，
+    # 否则 worker 只会打日志，状态永远停在 Downloading，UI 卡死。
+    try:
+        message = await fetch_message(client, message)
+    except Exception as fetch_err:
+        logger.warning(
+            f"Message[{getattr(message, 'id', '?')}] 拉取消息失败（可能连接断开）: {fetch_err}"
+        )
+        return DownloadStatus.FailedDownload, None
     try:
         for _type in media_types:
             _media = getattr(message, _type, None)
@@ -581,18 +589,23 @@ def _check_config() -> bool:
 
 
 async def worker(client: pyrogram.client.Client):
-    """Work for download task"""
+    """下载任务消费者协程"""
     while app.is_running:
+        message = None
+        node = None
         try:
             item = await queue.get()
             message = item[0]
-            node: TaskNode = item[1]
+            node = item[1]
 
             if node.is_stop_transmission:
+                # 主动中止：把队列里残留的下载中状态清掉，避免 UI 一直显示 Downloading
+                _release_stuck_task(node, message, DownloadStatus.SkipDownload)
                 continue
 
             if is_message_skipped(str(node.chat_id), message.id):
                 skip_message(str(node.chat_id), message.id)
+                _release_stuck_task(node, message, DownloadStatus.SkipDownload)
                 continue
 
             if node.client:
@@ -600,7 +613,39 @@ async def worker(client: pyrogram.client.Client):
             else:
                 await download_task(client, message, node)
         except Exception as e:
-            logger.exception(f"{e}")
+            logger.exception(f"worker 捕获到未处理异常: {e}")
+            # 关键修复：worker 吞异常时必须把状态推进，否则 finish_task 永远追不上 total_task
+            if node is not None and message is not None:
+                _release_stuck_task(node, message, DownloadStatus.FailedDownload)
+
+
+def _release_stuck_task(
+    node: "TaskNode",
+    message: "pyrogram.types.Message",
+    status: "DownloadStatus",
+):
+    """将异常/中断的任务从"下载中"状态释放，避免任务队列永久卡死。
+
+    做三件事：
+    1) 标记 download_status，让 UI 不再显示"下载中"。
+    2) 推进 finish_task，让 _wait_node_finish 能正常退出。
+    3) 清理 _download_result 残留条目，避免速度/列表脏数据。
+    """
+    try:
+        msg_id = getattr(message, "id", None)
+        if msg_id is None:
+            return
+        node.download_status[msg_id] = status
+        # finish_task 通过 app.set_download_id 推进；bot 模式下原逻辑也不走 set_download_id，
+        # 这里保持一致：非 bot 时才推进，避免重复计数。
+        if not node.bot:
+            try:
+                app.set_download_id(node, msg_id, status)
+            except Exception as inner:
+                logger.warning(f"释放卡死任务时 set_download_id 失败 msg_id={msg_id}: {inner}")
+        remove_download_entry(node.chat_id, msg_id)
+    except Exception as e:
+        logger.warning(f"释放卡死任务清理失败: {e}")
 
 
 async def download_chat_task(
@@ -657,52 +702,64 @@ async def download_chat_task(
         for message in skipped_messages:
             await add_download_task(message, node)
 
-    async for message in messages_iter:  # type: ignore
-        # Update checking progress for each message
-        increment_task_stat("checked_messages")
-        
-        meta_data = MetaData()
+    # 关键修复：消息迭代和缓存写入必须包进 try/finally，
+    # 否则中途抛 Connection lost 时 total_task 不会被回写，_wait_node_finish 误判频道已完成，
+    # 后续 worker 还在跑就被切到下一个频道，UI 永远显示"下载中"。
+    iter_completed = False
+    try:
+        async for message in messages_iter:  # type: ignore
+            # Update checking progress for each message
+            increment_task_stat("checked_messages")
 
-        caption = message.caption
-        if caption:
-            caption = validate_title(caption)
-            app.set_caption_name(node.chat_id, message.media_group_id, caption)
-            app.set_caption_entities(
-                node.chat_id, message.media_group_id, message.caption_entities
-            )
-        else:
-            caption = app.get_caption_name(node.chat_id, message.media_group_id)
-        set_meta_data(meta_data, message, caption)
+            meta_data = MetaData()
 
-        if app.need_skip_message(chat_download_config, message.id):
-            continue
-
-        if app.exec_filter(chat_download_config, meta_data):
-            # 改动点 B：通过 filter 的消息计数，作为 X/N 的分母实时递增
-            increment_task_stat("qualified_files")
-            await add_download_task(message, node)
-        else:
-            node.download_status[message.id] = DownloadStatus.SkipDownload
-            increment_task_stat("skipped_files")
-            if message.media_group_id:
-                await upload_telegram_chat(
-                    client,
-                    node.upload_user,
-                    app,
-                    node,
-                    message,
-                    DownloadStatus.SkipDownload,
+            caption = message.caption
+            if caption:
+                caption = validate_title(caption)
+                app.set_caption_name(node.chat_id, message.media_group_id, caption)
+                app.set_caption_entities(
+                    node.chat_id, message.media_group_id, message.caption_entities
                 )
+            else:
+                caption = app.get_caption_name(node.chat_id, message.media_group_id)
+            set_meta_data(meta_data, message, caption)
 
-    chat_download_config.need_check = True
-    chat_download_config.total_task = node.total_task
-    node.is_running = True
+            if app.need_skip_message(chat_download_config, message.id):
+                continue
+
+            if app.exec_filter(chat_download_config, meta_data):
+                # 改动点 B：通过 filter 的消息计数，作为 X/N 的分母实时递增
+                increment_task_stat("qualified_files")
+                await add_download_task(message, node)
+            else:
+                node.download_status[message.id] = DownloadStatus.SkipDownload
+                increment_task_stat("skipped_files")
+                if message.media_group_id:
+                    await upload_telegram_chat(
+                        client,
+                        node.upload_user,
+                        app,
+                        node,
+                        message,
+                        DownloadStatus.SkipDownload,
+                    )
+        iter_completed = True
+    finally:
+        # 不论遍历是否正常结束，都必须把 node.total_task 同步给 chat_download_config，
+        # 否则 _wait_node_finish 会用 total_task=0 的旧值立即返回，跳过对 worker 的等待。
+        chat_download_config.need_check = True
+        chat_download_config.total_task = node.total_task
+        node.is_running = True
 
     # 改动点 C：遍历正常完成，把实际 qualified_files 写入缓存并覆盖 estimated_total
     # 仅在正常完成时写入（异常/中断时不执行，避免脏缓存）
-    actual_total = get_task_progress().get("qualified_files", 0)
-    db.save_scan_cache(str(node.chat_id), filter_key, actual_total)
-    update_task_progress(estimated_total=actual_total, is_checking=False)
+    if iter_completed:
+        actual_total = get_task_progress().get("qualified_files", 0)
+        db.save_scan_cache(str(node.chat_id), filter_key, actual_total)
+        update_task_progress(estimated_total=actual_total, is_checking=False)
+    else:
+        # 异常中断时也要把 is_checking 关掉，避免 UI 一直显示"扫描中"
+        update_task_progress(is_checking=False)
 
 
 async def _wait_node_finish(chat_config, timeout: int = 3600):