[BUG] Desktop 2.110.1 (Windows MSIX): update checks regressed to Squirrel AutoUpdater — every check fails with 'Can not find Squirrel'

Summary

Since updating to Claude Desktop 2.110.1 on Windows (MSIX install), every background auto-update check fails immediately with Error: Can not find Squirrel, thrown from Electron's built-in AutoUpdater.checkForUpdates (the Squirrel-based updater, which does not apply to MSIX installs). The MSIX-aware update flow that worked in previous versions no longer runs, so the app can no longer detect or download new versions.

Environment

• Claude Desktop 2.110.1.0, MSIX package Claude_2.110.1.0_x64__pzs8sxrjxfjjc (SignatureKind: Developer, not Microsoft Store)
• Installed under C:\Program Files\WindowsApps\; originally migrated from a Squirrel install (log: [MSIX] Filesystem not virtualized — ... (likely Squirrel upgrade))
• Windows 11 Pro 10.0.26200

What worked before (up to 2.110.0)

The updater used a flow that logged Checking for updates → Found an update, downloading → Update downloaded and ready to install, and it successfully auto-updated five times between Sep 10 and Sep 17 (1.52386.0 → 1.52386.3 → 1.52386.6 → 2.110.0 → 2.110.1):

2026-09-17 09:58:57 [info] [updater] Host quiet after 1 busy min; checking for updates
2026-09-17 09:58:57 [info] [updater] Update URL: https://api.anthropic.com
2026-09-17 09:58:57 [info] [updater] Checking for updates
2026-09-17 09:58:59 [info] [updater] Found an update, downloading
2026-09-17 09:59:55 [info] [updater] Update downloaded and ready to install { releaseName: 'Claude 2.110.1' }
2026-09-17 10:09:56 [info] [updater] Staged version 2.110.1 is still current (latest: 2.110.1, lastTarget: null)

What happens since 2.110.1

The very first check after relaunching into 2.110.1 (same day, ~1h20m later) throws, and every check since then fails the same way — 36 consecutive failed checks between Sep 17 and Sep 23, zero successful Checking for updates runs:

2026-09-17 11:20:21 [info] [updater] Host quiet after 1 busy min; checking for updates
2026-09-17 11:20:21 [info] [updater] Update URL: https://api.anthropic.com
2026-09-17 11:20:21 [error] [updater] Auto-update error: Error: Can not find Squirrel
    at AutoUpdater.checkForUpdates (node:electron/js2c/browser_init:2:9056)
    at _7n (C:\Program Files\WindowsApps\Claude_2.110.1.0_x64__pzs8sxrjxfjjc\app\resources\app.asar\.vite\build\index.chunk-B9Ply7bK.js:13:2574015)
    at process.processTicksAndRejections (node:internal/process/task_queues:104:5)

MSIX detection itself still works at startup, so the app knows it is an MSIX install but routes the periodic check to the Squirrel AutoUpdater anyway:

2026-09-23 10:30:26 [info] [CCD-autoupdate] Disabled: MSIX install
2026-09-23 10:30:26 [info] [MSIX] Package family from exe path: Claude_pzs8sxrjxfjjc
2026-09-23 10:30:26 [info] [updater] App is installed, enabling initial check and auto-updates
2026-09-23 10:30:26 [info] [updater] MSIX detected: windowsStore=false, appPathMatch=true, source=appPath, exe=C:\Program Files\WindowsApps\Claude_2.110.1.0_x64__pzs8sxrjxfjjc\app\claude.exe

Expected behavior

On an MSIX install, periodic update checks should keep using the MSIX-aware flow (as in ≤ 2.110.0) instead of Electron's Squirrel AutoUpdater, which by design cannot work outside a Squirrel install.

Impact

MSIX users on 2.110.1 will never auto-update again; the only way forward is manually downloading and reinstalling from claude.ai/download.

Steps to reproduce

1. Have Claude Desktop installed as MSIX (sideloaded, windowsStore=false) on Windows 11.
2. Auto-update to 2.110.1 (worked fine from 2.110.0).
3. Watch %LOCALAPPDATA%\Claude\Logs\main.log: every periodic check logs Auto-update error: Error: Can not find Squirrel.