When PTB's general httpx pool is exhausted, it converts httpx.PoolTimeout
into telegram.error.TimedOut whose message states the request was *not*
sent to Telegram. The send retry loop treated all non-connect TimedOut as
non-retryable, so a pool timeout raised immediately, skipped all 3 retry
attempts, and was returned as retryable=False -- silently dropping the
message (agent responses, cron reports, etc.).
A pool timeout means the request never left the process, making it the
safest case to retry. Add _looks_like_pool_timeout() and treat it like a
connect timeout in both the in-loop retry decision and the outer retryable
determination, so pool timeouts flow through the existing backoff loop and
stay retryable on exhaustion.
Reported-by: q3874758 (#35610)
dc4de14377