Handle supergroup joins via chat_member updates

Send verification challenges when Telegram hides join service messages, and subscribe to chat_member polling updates.

Co-authored-by: Cursor <cursoragent@cursor.com>

bot/__main__.py

@@ -31,7 +31,10 @@ async def main() -> None:
 
     asyncio.create_task(sweeper_loop(bot=bot, cfg=cfg, db=db))
     try:
-        await dp.start_polling(bot, allowed_updates=dp.resolve_used_update_types())
+        allowed_updates = list(dp.resolve_used_update_types())
+        if "chat_member" not in allowed_updates:
+            allowed_updates.append("chat_member")
+        await dp.start_polling(bot, allowed_updates=allowed_updates)
     finally:
         await db.close()
 

bot/handlers.py

@@ -10,6 +10,7 @@ from aiogram.types import (
     CallbackQuery,
     ChatMemberAdministrator,
     ChatMemberOwner,
+    ChatMemberUpdated,
     InlineKeyboardButton,
     InlineKeyboardMarkup,
     Message,
@@ -87,6 +88,32 @@ def _challenge_kb(chat_id: int, user_id: int) -> InlineKeyboardMarkup:
     )
 
 
+async def _on_user_joined(
+    *,
+    bot: Bot,
+    cfg: Config,
+    db: Database,
+    chat_id: int,
+    user_id: int,
+    user_full_name: str,
+) -> None:
+    try:
+        if await _is_admin(bot, chat_id, user_id):
+            return
+    except TelegramBadRequest:
+        return
+
+    await db.delete_verified(chat_id=chat_id, user_id=user_id)
+    await _ensure_challenge(
+        bot=bot,
+        cfg=cfg,
+        db=db,
+        chat_id=chat_id,
+        user_id=user_id,
+        user_full_name=user_full_name,
+    )
+
+
 async def _ensure_challenge(
     *,
     bot: Bot,
@@ -162,15 +189,7 @@ async def on_new_members(message: Message, bot: Bot, cfg: Config, db: Database)
     for user in message.new_chat_members:
         if user.is_bot:
             continue
-        try:
+        await _on_user_joined(
-            if await _is_admin(bot, chat_id, user.id):
-                continue
-        except TelegramBadRequest:
-            continue
-
-        # Force verification on every (re)join: prevents bypass if user was verified earlier.
-        await db.delete_verified(chat_id=chat_id, user_id=user.id)
-        await _ensure_challenge(
             bot=bot,
             cfg=cfg,
             db=db,
@@ -180,6 +199,40 @@ async def on_new_members(message: Message, bot: Bot, cfg: Config, db: Database)
         )
 
 
+@router.chat_member()
+async def on_chat_member_updated(
+    event: ChatMemberUpdated,
+    bot: Bot,
+    cfg: Config,
+    db: Database,
+) -> None:
+    """
+    Supergroups (especially linked discussion groups) often hide join service messages.
+    In that case Telegram sends chat_member updates instead of new_chat_members.
+    """
+    chat_id = event.chat.id
+    if not _is_allowed_chat(cfg, chat_id):
+        return
+
+    user = event.new_chat_member.user
+    if user.is_bot:
+        return
+
+    old_status = event.old_chat_member.status
+    new_status = event.new_chat_member.status
+    if old_status not in ("left", "kicked") or new_status not in ("member", "restricted"):
+        return
+
+    await _on_user_joined(
+        bot=bot,
+        cfg=cfg,
+        db=db,
+        chat_id=chat_id,
+        user_id=user.id,
+        user_full_name=user.full_name,
+    )
+
+
 @router.callback_query(F.data.startswith("verify:"))
 async def on_verify(
     callback: CallbackQuery,