[BUG] [BUG] Auto-updater blocks main process event loop — Claude Desktop becomes unresponsive on Windows

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code

### What's Wrong?

While Claude Desktop was actively in use, a background auto-update (app updated to release "Claude 1.32885.1"; embedded Claude Code CLI component swapped 2.1.229 → 2.1.234) triggered a burst of main-process event-loop stalls, the worst being 5516ms. Windows then marked the app "Not Responding". Ending it via Task Manager did not reliably work, and restarting Claude was difficult — even after a full PC restart. This has now happened repeatedly (5 times).

### What Should Happen?

Background updates should not block the Electron main process / UI thread. The app should remain responsive during and after an update, and should not leave the process in an unrecoverable "Not Responding" state.

### Error Messages/Logs

```shell
[info] [updater] Update downloaded and ready to install { releaseName: 'Claude 1.32885.1' }
[warn] [event-loop-stall] main process blocked for 4284ms (task none, total 1, cumulative 4284ms, rss 331MB)
[warn] [event-loop-stall] main process blocked for 1672ms (task none, total 2, cumulative 5956ms, rss 329MB)
[info] [CCD] Installed at ...\claude-code\2.1.234\claude.exe
[warn] [CCD] Could not remove old version 2.1.229 (in use?): [Error: EPERM: operation not permitted, unlink '...\claude-code\2.1.229\claude.exe']
[warn] [event-loop-stall] main process blocked for 720ms (task none, total 1, cumulative 720ms, rss 328MB)
[warn] [event-loop-stall] main process blocked for 5516ms [likely sleep: duration_heuristic] (task none, total 1, cumulative 720ms, rss 331MB)
```

### Steps to Reproduce

1. Use Claude Desktop normally with an active session (in our case: a Browser Preview session was warm).
2. Let a background app update download and begin installing while the app stays open/in use.
3. Observe main-process event-loop stalls in %APPDATA%\Claude\logs\main.log around the update timestamp.
4. If a stall exceeds ~5s, Windows marks the app "Not Responding"; recovery is unreliable via Task Manager.
Note: not manually/deterministically reproducible on demand — depends on an update landing while the app is in active use. Reproduced 5 times over the past week per user report.

### Claude Model

None

### Is this a regression?

Yes, this worked in a previous version

### Last Working Version

_No response_

### Claude Code Version

2.1.198 (Claude Code) — standalone CLI per `claude --version`. Note: embedded CCD component inside Claude Desktop shows 2.1.229→2.1.234 in logs, suggesting two separate installs.

### Platform

Anthropic API

### Operating System

macOS

### Terminal/Shell

Terminal.app (macOS)

### Additional Information

This affects Claude Desktop (Electron shell), not just the CLI. No Crashpad report was generated for these hangs (Crashpad/reports empty) — consistent with a main-thread hang rather than a crash. System RAM was never under pressure (stable ~1.3-2.1GB / 98GB free). Orphaned version folder "2.1.229" still present on disk next to "2.1.234" due to the failed EPERM cleanup.

Start by examining the Electron desktop auto-updater and the embedded Claude Code component installation path; the report does not name source files or tests. Review the main-process event-loop stall logs alongside update installation and old-version cleanup on Windows. Done means updates no longer make the app unresponsive; the issue gives no deterministic reproduction steps or test target.

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