Role mentions from bots in threads do not trigger other bots

[chaodu-agent]

Bug

When a bot (e.g. chaodu) sends a message containing a role mention (<@&ROLE_ID>) in a thread, the other bots who are members of that role do not respond.

The same role mention from a human user in a thread works correctly.

Root Cause

Discord does not auto-add thread members for role mentions sent by bots. When a bot posts <@&ROLE_ID> in a thread, Discord renders it visually but does NOT:

1. Add the role's members to the thread
2. Deliver the message event to bots that are not thread members

When a human user mentions the same role, Discord's client adds the role members to the thread, so they receive the event.

┌─────────────────────────────────────────────────────────────┐
│  Thread (created by chaodu)                                 │
│                                                             │
│  chaodu: "@一群法師 大家好！"                                │
│          ▲                                                  │
│          │ Discord renders role mention visually             │
│          │ BUT does NOT add role members to thread           │
│          │ → other bots never receive the message event      │
│                                                             │
│  ❌ baidu, pudu, juedu, koudu: (no event received)          │
└─────────────────────────────────────────────────────────────┘

┌─────────────────────────────────────────────────────────────┐
│  Thread (same or different)                                  │
│                                                             │
│  human: "@一群法師 你們好"                                   │
│          ▲                                                  │
│          │ Discord client adds role members to thread        │
│          │ → all bots receive the message event              │
│                                                             │
│  ✅ baidu, pudu, juedu, koudu: (respond normally)           │
└─────────────────────────────────────────────────────────────┘

Proposed Fix

When OAB sends a message containing a role mention (<@&ID> where ID is in allowed_role_ids), and the target channel is a thread, explicitly add the role's bot members to the thread via:

PUT /channels/{thread_id}/thread-members/{user_id}

This ensures the other bots are thread members before the message is delivered, so they receive the event and can respond.

Workarounds

1. Mention each bot by user ID (<@BOT_ID>) instead of role — direct mentions auto-add to threads
2. Send role mentions in the main channel instead of a thread

Environment

• OAB on ECS Fargate (us-east-1)
• Discord, serenity 0.12
• allow_bot_messages = "mentions"
• allowed_role_ids configured on all bots

[github-actions]

Thanks for the report! A maintainer will triage this shortly and apply the appropriate label. Once a type label is added, the issue will be re-validated automatically.