fix: prevent message loss when new message arrives as idle timeout fires

[dptts]

Type of Change

• Skill - adds a new skill in .claude/skills/
• Fix - bug fix or security fix to source code
• Simplification - reduces or simplifies source code

Description

I added added support for agents to respond to webhooks and found a race condition. GroupQueue.sendMessage() could silently drop incoming messages.

Sequence:

1. Container is active processing messages (state.active = true)
2. Agent finishes its turn and enters idle-wait — the orchestrator's idle timer fires and calls closeStdin(), which writes a _close sentinel to the IPC directory and signals the container to wind down
3. A new user message arrives before the container process has actually exited — state.active is still true
4. sendMessage() passes its guard (!state.active || !state.groupFolder || !state.isTaskContainer) and writes the new message's IPC file into the input directory
5. The container reads _close, exits — the IPC file is never processed. Message silently lost.

Fix

Add a closing: boolean flag to GroupState. closeStdin() sets it; notifyContainerStart() clears it (reset for the next run). The sendMessage() guard gains || state.closing, making it return false during the window between idle-timeout and container exit. The caller then treats this as a queued pending message, which is processed in the next container run.

Evidence

The regression test in this PR (src/group-queue.test.ts) was written to fail on unfixed code and pass on the fix.

For Skills

• I have not made any changes to source code
• My skill contains instructions for Claude to follow (not pre-built code)
• I tested this skill on a fresh clone

[apatella]

The fix logic looks reasonable — the race between an incoming message and the idle timeout firing is a real edge case worth handling.

Two files need Prettier formatting before CI will pass:

• src/group-queue.ts
• src/group-queue.test.ts

Quick fix:

npx prettier --write src/group-queue.ts src/group-queue.test.ts

Once formatted, CI should be green. Nice catch on this bug! 👍