Bug

When [[reply_to_current]] is used in a Mattermost thread fork session, the reply fails with:

Mattermost API 400 Bad Request: Invalid RootId parameter.

Root Cause

In extensions/mattermost/src/mattermost/monitor.ts:764, payload.replyToId takes priority over threadRootId:

replyToId: payload.replyToId || threadRootId,

When [[reply_to_current]] resolves, it sets replyToId to the inbound message ID. If that inbound message is itself a threaded reply (has a non-empty root_id), this ID gets passed as root_id to the Mattermost API. Mattermost rejects it because root_id must reference the actual root post of a thread — a post that itself has a root_id cannot be used as a thread root.

Steps to Reproduce

1. Send a top-level DM message (post A)
2. Bot replies in thread (post B, root_id=A)
3. User replies in thread (post C, root_id=A)
4. Thread fork session is created, bot replies with [[reply_to_current]]
5. replyToId resolves to post C's ID
6. root_id is set to post C's ID → 400 Bad Request

Suggested Fix

When threadRootId is available, prefer it over payload.replyToId for the root_id field, since Mattermost does not support nested threading. Alternatively, when replyToId is set, resolve the target post's own root_id and use that if it exists.

// Instead of:
replyToId: payload.replyToId || threadRootId,

// Either:
replyToId: threadRootId || payload.replyToId,

// Or resolve the root if replyToId is itself a threaded reply

Environment

• OpenClaw running on K8s
• Mattermost Team Edition 10.11.10
• Thread fork sessions with [[reply_to_current]]