Renaming a Telegram bot's @username in BotFather silently stopped the
gateway from answering in groups.
PTB caches getMe() in Bot._bot_user and only rewrites it inside get_me(),
so after a rename the adapter kept comparing mentions against the OLD
handle. The exclusive-mention gate then saw the new @handle, failed to
match itself, and concluded the message was addressed to a different bot
— dropping it before the reply and wake-word fallbacks could run. Native
replies to the bot were discarded too. Polling mode recovered on the next
90s heartbeat; webhook mode never calls get_me() again, so it stayed dead
until restart.
Separately, the bot-handle pattern assumed every bot username ends in
"bot". Collectible (Fragment) usernames can be assigned to bots and drop
that suffix (@jarvis, @pic), so such a bot could not recognise its own
handle in the entity-less fallback and was suppressed by any message that
also named another bot.
- Route every mention comparison through _current_bot_username(), which
prefers the last observed handle over PTB's cache.
- Learn the live handle from inbound updates: Telegram stamps the current
username on our own messages and on reply_to_message. Guarded by user
id, so another account's handle is never adopted.
- Re-check identity out of band (TTL-bounded, one getMe per 5 min) when
the exclusive gate is about to drop a message — the exact stale-handle
symptom — so the mistake self-corrects instead of persisting.
- Refresh identity in webhook mode via a dedicated low-frequency loop,
cancelled on the same teardown fence as the heartbeat.
- Match our own handle by identity rather than shape. Foreign handles keep
the deliberate "...bot" narrowing so human @handles still never act as
routing hints (the intent behind ce4d857021).
Validation: 11 regression tests; sabotage runs confirm each behavioral
test fails with the fix reverted. 157 tests green across the Telegram
gating, reconnect, and topic-mode suites.
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