Discord parity: forum/media posting + multi-bot agent routing

[adhikjoshi]

Problem

Spacebot’s Discord adapter is strong for channels/threads, but it still misses a few practical features that OpenClaw users rely on in community servers.

Gaps

1. Forum/media parent posting flow is missing

   • Current implementation creates PublicThread for OutboundResponse::ThreadReply and falls back to plain message on failure.
   • There is no explicit handling for Discord forum/media parent channels where posting requires creating a thread-with-starter message.
   • In practice this means forum workflows are inconsistent compared to regular channels.

2. No named multi-bot adapter support yet

   • Current config exposes a singleton messaging.discord.token.
   • There is a design doc for named adapters, but this is not implemented.
   • This blocks setups with multiple Discord bots mapped to different agents in one Spacebot instance.

3. Agent-level mention routing is too limited for multi-agent Discord communities

   • Routing is currently binding-first and first-match-wins.
   • Mention gating is bot-level (@this bot / reply-to-bot), not agent-level (@agent-A, @agent-B with separate bot identities or adapter keys).
   • This makes “10 agents in one Discord server, mention to route” hard to operate cleanly.

Requested parity behavior

• Support forum/media channel send semantics:
  • If target is a forum/media parent, create a thread post with starter content.
  • Keep thread title derivation predictable (e.g. first non-empty line fallback).
• Implement named Discord adapter instances (default + named), and allow bindings to choose adapter instance.
• Preserve backward compatibility for existing single-token config.
• Expose clear routing behavior when multiple bindings/agents are in the same guild.

Suggested acceptance criteria

• Sending to a forum/media parent creates a valid forum thread post.
• Multiple Discord bot tokens can run simultaneously on one instance.
• bindings can target both agent_id and adapter instance deterministically.
• Mention routing docs cover multi-agent patterns and edge-cases.

Why this matters

These are core migration blockers for OpenClaw users running larger Discord communities, where forum workflows and multi-bot/multi-agent routing are essential.