Cowork/Workspace EXDEV rename fails within the SAME directory (not just cross-Temp/Roaming) — MSIX install, v1.19367.0.0

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?

Claude Desktop's Workspace/Cowork VM fails to start on every attempt with an EXDEV error. Unlike most reported cases where the rename crosses %TEMP% → %APPDATA%, in this case source and destination are in the exact SAME directory (claudevm.bundle), which suggests this isn't purely the typical MSIX Local/Roaming VFS boundary issue.

Environment:

• Claude Desktop version: 1.19367.0.0
• Install type: MSIX (via official Setup.exe from claude.ai/download — note this still installs as MSIX)
• Package family: Claude_pzs8sxrjxfjjc
• OS: Windows 10.0.26200.8737

Extensive troubleshooting already attempted, all failed to resolve:

• Full uninstall of MSIX package + reinstall via official .exe (still installs as MSIX)
• Deleted vm_bundles folder and let it regenerate
• Disabled luafv filter + reboot — no change
• Disabled CldFlt filter + reboot — no change (re-enabled afterward)
• Verified %TEMP% and %APPDATA% are on the same drive (C:)
• Verified "Controlled folder access" is off
• Verified 289 GB free disk space (ruled out ENOSPC)
• Verified OneDrive Known Folder Move does NOT include AppData
• No third-party antivirus (Windows Defender only)
• Manual test: created + renamed a test file directly in vm_bundles via PowerShell — succeeded with no error, confirming the OS/filesystem itself can perform the rename fine in that location

What Should Happen?

VM bundle download and placement should complete successfully, or the app should fall back to copyFile()+unlink() when rename() fails with EXDEV, regardless of MSIX virtualization boundaries.

Error Messages/Logs

From cowork_vm_node.log:

2026-07-08 22:01:14 [error] [download] VM download failed: EXDEV: cross-device link not permitted, rename 'C:\Users\ellli\AppData\Roaming\Claude\vm_bundles\claudevm.bundle\rootfs.vhdx.tmp' -> 'C:\Users\ellli\AppData\Roaming\Claude\vm_bundles\claudevm.bundle\rootfs.vhdx'
    at async Object.rename (node:internal/fs/promises:785:10)
    errno: -4037,
    code: 'EXDEV',
    syscall: 'rename'

Also seen earlier in the same log, same pattern with the .zst partial file:
"message": "EXDEV: cross-device link not permitted, rename 'C:\\Users\\ellli\\AppData\\Roaming\\Claude\\vm_bundles\\claudevm.bundle\\rootfs.vhdx.zst.21237ca86d15.partial' -> 'C:\\Users\\ellli\\AppData\\Roaming\\Claude\\vm_bundles\\claudevm.bundle\\rootfs.vhdx.zst'"

Note: real logs are located under the virtualized MSIX path, not the path shown in the error message:
C:\Users\ellli\AppData\Local\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\logs\

Steps to Reproduce

1. Install Claude Desktop for Windows via the official .exe from claude.ai/download (installs as MSIX package Claude_pzs8sxrjxfjjc)
2. Open Claude Desktop and navigate to Cowork/Workspace
3. Attempt to start the Workspace
4. Observe: rootfs.vhdx downloads, but the final rename() from the .tmp/.partial file to the final filename fails with EXDEV every time
5. This is 100% reproducible — occurs on every single attempt, across multiple days and multiple reinstalls

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

N/A — this is a Claude Desktop / Cowork issue, not Claude Code CLI. Filing here as there is no dedicated Claude Desktop issue tracker (see similar precedent in issues #38457, #36642).

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_