When the connection pool is in a degraded state after
_drain_polling_connections(), start_polling() can hang indefinitely
when both primary and fallback Telegram endpoints are unreachable. The
httpx client may hold a stale socket that neither connects nor times out
within PTB's internal flow, causing the reconnect ladder to stall at
attempt 1/10 forever.
Wrap start_polling() in asyncio.wait_for() with a 30-second timeout so a
hung call raises asyncio.TimeoutError and feeds back into the existing
retry ladder. This unblocks:
- The 10-retry ladder advances to attempt 2, 3, ...
- The heartbeat loop sees _polling_error_task.done() and can trigger recovery
- The reconnect watcher gets the adapter in _failed_platforms
Fixes#59614
liuhao1024
4aaaa206aa