replyToMode 自动注入回复锚点，线程回复真正可控（PR #15011）

• Channel supports threaded or reply-style messaging (e.g., Telegram/Slack).
• Channel config enables replyToMode with value first or all.
• You can reproduce at least one case where replies were previously sent as plain messages.

1. Set replyToMode in channel config and restart gateway with PR #15011 included.
2. Send a trigger message without manually adding [[reply_to_current]] and capture the assistant response.
3. Verify response payload now carries replyToId/currentMessageId mapping before filtering.
4. Test multi-block responses to ensure both final-reply and block-streaming paths keep threading behavior.
5. Document per-chat-type override strategy (direct/group/thread) to avoid over-threading.

• Some channels flatten replies by design; message may still appear in main feed depending on provider UX（需验证）。
• If custom middleware rewrites payloads post-filter, it may override reply threading behavior.

This tip is aggregated from community/public sources and preserved with attribution.