Greptile Summary

This PR fixes a bug where the Matrix plugin ignored agent-level mentionPatterns configuration because buildMentionRegexes was called without an agentId. The fix moves resolveMatrixInboundRoute earlier in the message-handling flow so that _route.agentId is available when building mention regexes, which are then used consistently throughout the handler.

Key changes:

• resolveMatrixInboundRoute is now called before mention detection, providing the agentId needed for agent-scoped mention patterns.
• agentMentionRegexes (built with agentId) replaces the previously static mentionRegexes parameter for all mention checks and canDetectMention logic.
• Test harnesses are updated to mock core.channel.mentions.buildMentionRegexes, and assertions on resolveAgentRoute call-counts in drop-path tests are removed since route resolution now always runs before the bot-allow gating.
• One cleanup opportunity remains: the mentionRegexes field in MatrixMonitorHandlerParams and its corresponding destructure in createMatrixRoomMessageHandler are now unused dead code — the handler never reads the value. The counterpart in index.ts (buildMentionRegexes(cfg) without an agentId and the resulting pass-through) could also be removed.

Confidence Score: 4/5

• PR is safe to merge — the core fix is correct and all 34 tests pass. One minor dead-code cleanup (the mentionRegexes param) can be done as a follow-up.
• The logic change is well-scoped: route resolution is moved earlier with no new side effects, and the correct agentId is now threaded into mention-pattern building. Tests are updated to match the new control flow. The only issue is that the old mentionRegexes parameter on MatrixMonitorHandlerParams (and its usage site in index.ts) is now dead code, which is a style/cleanup concern and not a functional bug.
• extensions/matrix/src/matrix/monitor/handler.ts (line 65 & 157) and extensions/matrix/src/matrix/monitor/index.ts (line 167 & 226) — the now-unused mentionRegexes param should be cleaned up.

This is a comment left during a code review.
Path: extensions/matrix/src/matrix/monitor/handler.ts
Line: 157

Comment:
**`mentionRegexes` param is now dead code**

After this PR the handler always derives mention regexes dynamically via `core.channel.mentions.buildMentionRegexes(cfg, _route.agentId)` (line 543) and never references the `mentionRegexes` value that was destructured from params. The destructured variable on this line is unused, meaning:

1. The `mentionRegexes` field in `MatrixMonitorHandlerParams` (line 65) is now dead.
2. The destructuring here is unused — a TypeScript `noUnusedLocals` check would flag it.
3. In `index.ts:167`, `buildMentionRegexes(cfg)` is still called (without an `agentId`) and the result passed to the handler — that call is now a no-op from the handler's perspective.

Consider removing the `mentionRegexes` field from `MatrixMonitorHandlerParams`, the destructuring here, and the corresponding build+pass in `index.ts` to avoid misleading future readers into thinking the param still affects mention matching.

How can I resolve this? If you propose a fix, please make it concise.

_{Last reviewed commit: "fix(matrix): resolve..."}