Greptile Summary

This PR fixes a bug where mention regexes were built once at startup without agent context, meaning multi-agent deployments would always use the default agent's mention patterns regardless of which agent a message was routed to. The fix resolves the agent route before mention detection on every incoming message, then builds regexes using the correct agentId.

Key changes:

• resolveAgentRoute is moved earlier in handler.ts (before resolveMentions), so buildMentionRegexes(cfg, baseRoute.agentId) can be called with the correct per-message agent context.
• The startup-time buildMentionRegexes(cfg) call in index.ts and the corresponding mentionRegexes handler parameter are removed, eliminating the stale cached regexes.
• A regression test assertion is added confirming buildMentionRegexes receives the routed agentId ("main") rather than being called with no agent context.

Trade-off to note: resolveAgentRoute is now called for every message that passes pre-mention-check filtering (DM policy, room gating, etc.), including messages that will subsequently be dropped due to no-mention. This is a minor performance consideration but is unavoidable to support agent-aware regex building at the correct point in the pipeline.

Confidence Score: 5/5

• This PR is safe to merge — it is a targeted correctness fix with no regressions introduced.
• The change is narrow in scope: it moves one existing function call (resolveAgentRoute) earlier in the handler to enable per-message agent-aware mention regex building. All required variables are in scope at the new call site. The result is reused later (for route construction), so there is no duplicated work. The startup-time cached regexes are cleanly removed, and a new regression assertion confirms the agent ID flows through correctly. No new error paths are introduced.
• No files require special attention

_{Last reviewed commit: e33e504}

Maintainer-ready summary:

• Scope: Matrix mention routing fix for multi-agent setups.
• Behavior: mention regexes are now built with the resolved agentId per message, not once globally at startup.
• Risk: low; localized to Matrix monitor mention detection flow.
• Coverage: adds/updates regression assertion that buildMentionRegexes is called with the routed agent.
• CI: running.

If this shape looks right, this should be safe to merge as a targeted behavior fix.

Friendly ping: this PR is currently clean with required checks green. If the scope looks good, this should be ready for maintainer merge.

Closing this to reduce stale PR inventory and reset on smaller, higher-signal work. If needed, I can reopen or resubmit a tighter replacement later.