[BUG] Cowork regression — Windows 11, previously working, now shows yukonSilver unsupported after auto-update (v1.3109.0.0)

Preflight Checklist

• [x] I have searched existing issues 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?

Preflight Checklist

• [x] I have searched existing issues
• [x] This is a single bug report
• [x] I am using the latest version of Claude Desktop

What's Wrong?

Cowork was previously installed and working correctly on this user's Windows machine. After an auto-update, the Cowork tab no longer appears in the navigation — only Chat and Code are visible. System hardware and Windows edition are unchanged.

This matches the regression pattern described in #28238, #43966, #47327, #48995, and #50495. The original yukonSilver bug was reportedly fixed in v1.1.2998, but regressions have continued across subsequent versions.

Note: this is a regression, not a fresh-install case. The code path is demonstrably capable of working on this machine — it was working until the auto-update.

Environment

• App version: 1.3109.0.0
• OS: Windows 11 [Pro / Business — confirm with Jess]
• Architecture: x64
• Subscription: Claude Team (Standard seat)
• Organisation: Cowork enabled at org level, other users on same plan/seat tier have Cowork working
• Previously working: Yes, installed March 2026, Cowork worked initially
• Broke after: Auto-update (exact version unknown)

What Should Happen?

Cowork tab should remain visible after auto-updates on machines where it was previously working. At minimum, regressions on previously-working installs should be prioritised over fresh-install detection bugs, since they prove the platform is compatible.

Error Messages/Logs

Steps to Reproduce

1. Install Claude Desktop on Windows 11 in March 2026 — Cowork works
2. Allow auto-update to run
3. Observe: Cowork tab no longer appears, only Chat and Code visible
4. Full uninstall/reinstall does not restore Cowork

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

1.3109.0.0

Platform

Other

Operating System

Windows

Terminal/Shell

Other

Additional Information

This is affecting a paying Team customer. Multiple users across the same organisation are on identical plans — only this specific machine is affected, suggesting a local state or detection issue introduced by a recent update. Happy to provide logs via support ticket on request.