When a Telegram long-poll TCP socket enters CLOSE-WAIT (remote sent FIN
but httpx hasn't noticed), epoll still reports it readable so no
exception is raised. PTB's error_callback never fires, the reconnect
ladder never engages, and the gateway silently stops receiving messages
while the process stays alive — until a manual systemctl restart.
The existing recovery only covers two cases: error_callback-driven
reconnects (which require an exception PTB never gets) and a one-shot
_verify_polling_after_reconnect probe (which runs only right after an
explicit reconnect). A socket that wedges during steady-state operation
is never detected.
Add _polling_heartbeat_loop: a background asyncio.Task started in
connect() (polling mode only) that probes get_me() every 90s on the
general request pool (not the getUpdates pool, so healthy long-polls are
never interrupted). On asyncio.TimeoutError/OSError it hands off to the
existing _handle_polling_network_error ladder; other errors are
swallowed. disconnect() cancels and awaits the task. Worst-case
detection window ~105s.
Complementary to #51541 (general-pool keepalive limits / fd leak) — that
recycles idle pooled connections; this detects a wedged active read.
Fixes#48495
Co-authored-by: agt-user <267614622+agt-user@users.noreply.github.com>
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