On some networks (university, corporate), api.telegram.org resolves to a
valid Telegram IP that is unreachable due to routing/firewall rules. A
different IP in the same Telegram-owned 149.154.160.0/20 block works fine.
This adds automatic fallback IP discovery at connect time:
1. Query Google and Cloudflare DNS-over-HTTPS for api.telegram.org A records
2. Exclude the system-DNS IP (the unreachable one), use the rest as fallbacks
3. If DoH is also blocked, fall back to a seed list (149.154.167.220)
4. TelegramFallbackTransport tries primary first, sticks to whichever works
No configuration needed — works automatically. TELEGRAM_FALLBACK_IPS env var
still available as manual override. Zero impact on healthy networks (primary
path succeeds on first attempt, fallback never exercised).
No new dependencies (uses httpx already in deps + stdlib socket).
Add reply_to_mode setting (off/first/all) to control whether Telegram
replies quote/thread to the user's original message.
- 'off': Never thread replies (no quote bubble)
- 'first': Only first chunk threads to user's message (default, preserves existing behavior)
- 'all': All chunks in multi-part replies thread to user's message
Configurable via:
- reply_to_mode in platform config (gateway config YAML)
- TELEGRAM_REPLY_TO_MODE env var
Based on PR #855 by raulvidis.
