[BUG] macOS desktop app: messages typed during an active turn are sent immediately instead of being queued

## Summary

In the Claude Desktop app (Code tab), typing a message and pressing Enter **while the assistant turn is still in flight** does not queue the message. The message is submitted immediately instead of waiting for the current turn to finish.

## Environment

- Claude Desktop `1.52386.6` (CFBundleShortVersionString / CFBundleVersion both `1.52386.6`)
- macOS 15.6 (Darwin 25.6.0), Apple Silicon
- Claude Code session running inside the desktop app (Code tab), model Opus 5

## Steps to reproduce

1. Open a session in the Code tab.
2. Send a prompt that takes a while (e.g. one that runs several tool calls).
3. While the assistant is visibly still working (streaming text / running tools), type a follow-up message and press Enter.

## Expected

The follow-up is held as a queued message and delivered when the current turn completes (the documented queueing behavior).

## Actual

The message is sent right away rather than being queued — no queued-message indicator appears.

## Notes

- Reproduced by the user across multiple attempts, including while the turn was clearly active.
- Nothing queue-related appears in `~/Library/Logs/Claude/main.log` or `main-window.log`; the only `queue` matches are unrelated (`flushEventQueue` on quit, `change_directory queued`, and `enqueue=Nms` in `[CCD start-timing]` lines). This looks like renderer-side behavior that is not logged, so there is no diagnostic output to attach.
- Searched open issues for "queued messages" / "message queue"; the closest ones (#87656, #93659, #77451, #93276) describe different symptoms (fold-mid-turn setting, Esc delivery, loss on session switch, iPadOS stuck turn), not "queueing never engages on macOS desktop".