Summary

Three related improvements for the Feishu extension that significantly improve group chat UX:

1. Always reply in thread — Add reply_in_thread: true to all im.message.reply calls in send.ts
2. Parallel group timeline sessions — Use messageId as topic key for timeline messages (no rootId) so each message gets its own independent session
3. Reply to thread root — Use ctx.rootId || ctx.messageId as replyToMessageId so replies go to the thread root instead of creating nested sub-threads
4. Fire-and-forget message handling — Remove await on message dispatch in WebSocket mode (monitor.ts) so messages are processed in parallel without blocking the event loop

Motivation

Currently in group chats:

• Bot replies appear on the main timeline, cluttering the chat
• Messages are processed sequentially — if one takes 30s, the next one waits
• Replying to a message inside a thread creates a nested sub-thread instead of keeping the conversation flat within the existing thread
• Timeline messages in the same group share a single session, causing context mixing

These issues make the bot unusable in active group chats with multiple concurrent users.

Proposed Changes

1. reply_in_thread: true in send.ts

Add reply_in_thread: true to the data payload in all im.message.reply API calls. This keeps bot responses contained in threads.

2. Parallel group sessions in bot.ts

When topicSessionMode is enabled for a group, use ctx.rootId ?? ctx.messageId as the topic key instead of only ctx.rootId:

• Thread replies (rootId present): share session by thread root (existing behavior)
• Timeline messages (no rootId): each message gets its own session via messageId

This enables true parallel processing in group chats.

3. Reply to thread root in bot.ts

Change replyToMessageId: ctx.messageId → replyToMessageId: ctx.rootId || ctx.messageId so that replies within a thread always target the root message, avoiding nested sub-threads.

4. Fire-and-forget in monitor.ts

In the WebSocket message handler, always use fire-and-forget (.catch() without await) regardless of the fireAndForget flag. Combined with per-message sessions (point 2), this is safe and dramatically improves throughput.

Related

• Feishu: Sub-agent replies create new topics instead of replying in the original topic thread #10773 — Sub-agent replies creating new topics (related but focuses on sub-agent routing)
• Feature: Thread-session binding — route sub-agent I/O through platform threads #15217 — Thread-session binding

Environment

• Feishu extension: extensions/feishu/src/send.ts, bot.ts, monitor.ts
• Tested with topicSessionMode: "enabled" in group config