Telegram Bot API 10.0 can push agent replies out of private topics
A fresh Telegram Bot API 10.0 regression is now worth treating as an operator risk, not just a channel bug. Reports show private-chat topic replies that used to work with message_thread_id now return “Bad Request: message thread not found”. Hermes then falls back to sending without the thread id, which can move replies into the bot’s main “All Messages” chat instead of the original topic. The underlying tdlib issue says inbound topic ids are still present, while outbound sendMessage to the same id fails; direct_messages_topic_id may be the new working path for private bot topics.
Topic routing is part of the safety and usability boundary for chat-based agents. A silent fallback to the parent chat can confuse operators, leak context across topic workflows, and make a working bot look unreliable even when the model and gateway are healthy.
- Hermes issue #22022 reports private Telegram topic replies failing with “message thread not found” after Bot API 10.0, then falling back into All Messages
- The same Hermes report includes raw API tests where message_thread_id fails for private topic ids but direct_messages_topic_id succeeds
- tdlib/telegram-bot-api issue #847 tracks sendMessage with message_thread_id failing for private chat topics after the May 8 Bot API 10.0 rollout
- The upstream issue notes incoming updates still include message_thread_id, so the break is on outbound delivery rather than missing inbound topic metadata
- The upstream Telegram behavior may change again without an agent release
- The issue is specific to private bot topics; forum and supergroup thread handling should not be changed blindly
- Silent fallback is the dangerous part for operators who use topics as separate workspaces or approval lanes