The main bot is now an admin in the moderated discussion group and receives its
messages (allowed_updates includes message). Its default handler replied to
every message with a Mini App launch button — an inline web_app button, which
Telegram permits only in private chats — so replying in the group failed with
BUTTON_TYPE_INVALID (silently: the send fails, no user-facing error). Reply only
in a private chat; in the group the bot only manages permissions. The promo bot
gets the same guard.