A single Telegram 409 Conflict from getUpdates permanently killed
Telegram polling with no recovery possible (retryable=False on
first occurrence). This is too aggressive for production use with
process supervisors.
Transient 409s are expected during:
- --replace handoffs where the old long-poll session lingers on
Telegram servers for a few seconds after SIGTERM
- systemd Restart=on-failure respawns that overlap with the dying
instance cleanup
Now _handle_polling_conflict() retries up to 3 times with a
10-second delay between attempts. The 30-second total retry window
lets stale server-side sessions expire. If all retries fail, the
error is still marked as permanently fatal — preserving the original
protection against genuine dual-instance conflicts.
Tests updated: split the single conflict test into two — one verifying
retry on transient conflict, one verifying fatal after exhausted
retries.
Closes#2296
488a30e879