Description

When the bot receives an @mention inside a Teams channel thread, the reply is posted as a new top-level channel message instead of within the same thread.

The Bot Framework inbound activity provides the thread root message ID, and the inbound handler in message-handler.ts correctly saves it as replyToId on the StoredConversationReference. However, by the time the reply is sent, replyStyle resolves to "top-level", so the stored replyToId is never used to route the reply into the thread.

The messenger infrastructure for thread replies already exists (buildActivity handles threadRootId, sendProactively constructs the ;messageid= conversation ID). The gap is in the policy resolution and the send path.

Root Cause

Two independent issues:

1. Reply policy defaults replyStyle to "top-level" when requireMention: false -- resolveMSTeamsReplyPolicy() in policy.ts defaults replyStyle based on the requireMention setting. When requireMention is false, replyStyle defaults to "top-level" regardless of whether the inbound message came from a thread. Setting replyStyle: "thread" explicitly in config does not fully resolve the issue either.

2. send.ts hardcodes replyStyle: "top-level" -- The proactive send path in send.ts (~line 328) hardcodes replyStyle: "top-level" when calling sendMSTeamsMessages, ignoring thread context entirely. This affects messages sent via the message tool.

Steps to Reproduce

1. Configure msteams channel with requireMention: false
2. @mention the bot in a Teams channel -- bot responds (as a top-level post)
3. @mention the bot again inside the thread of any channel message
4. Expected: Bot replies within the same thread
5. Actual: Bot replies as a new top-level channel post

Confirmed via debug logging:

• Inbound: conversationRef.replyToId=1774246097310 (correct thread root ID)
• Outbound: replyStyle=top-level, threadRootId=undefined (thread context lost)

Related Issues

• [Bug]: msteams implicit mention fails — replyToId unreliable, conversation.id threadRootId not used as fallback #38629 -- replyToId unreliable for implicit mention detection (related but distinct: that's about detecting thread replies, this is about replying into threads)

Version

Tested on OpenClaw 2026.3.13, @openclaw/msteams extension.