enhancement: resolve role mentions to @RoleName instead of @unknown

[chaodu-agent]

Background

Follow-up from PR #364 review.

resolve_mentions (introduced in #364) correctly resolves user mentions to @DisplayName, but role mentions (<@&ROLE_ID>) fall through to the fallback and become @unknown. This loses semantic context — if a user typed @Admin, the agent should ideally see @Admin, not @unknown.

Suggested Approach

1. Use msg.mention_roles to get role IDs mentioned in the message
2. Look up role names from the guild cache (guild.roles)
3. Resolve <@&ROLE_ID> → @RoleName before the fallback step

If guild cache is not readily available, a lighter alternative is to replace <@&ID> with @role:ID instead of @unknown, preserving at least some context.

Related

• PR fix: resolve mentions instead of stripping all (#363) #364
• Issue bug: strip_mention removes all mentions from prompt, breaking bot-to-bot @mention visibility #363

DC: https://discord.com/channels/1491295327620169908/1494031440482926706

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