The existing `closed` flag in `createTypingCallbacks` guards
`onReplyStart` but not `fireStart` itself. If a keepalive tick is
already in-flight when `fireStop` sets `closed = true` and calls
`keepaliveLoop.stop()`, the running `onTick → fireStart` callback
still completes and sends a stale `sendChatAction('typing')` after
the reply message has been delivered.
On Telegram (which has no cancel-typing API), this causes the typing
indicator to linger ~5 seconds after the bot's message appears.
Add a `closed` early-return in `fireStart` as defense-in-depth so
that even an in-flight tick is suppressed once cleanup has started.
97eb5542e8