[BUG] Windows-MCP extension fails with egg_base build error on MSIX install (Windows 11 Pro)

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?

The Windows-MCP extension fails to start with "Server disconnected". Logs show:

error: error in 'egg_base' option: '.' does not exist or is not a directory
Confirmed uv is correctly installed and in PATH
Manually running "C:\WINDOWS\system32\uv.exe" --directory "C:\Users\[user]\AppData\Local\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\Claude Extensions\ant.dir.cursortouch.windows-mcp" run windows-mcp works fine and starts the server successfully.
The extension's .mcp manifest specifies "command": "uvx", "args": ["windows-mcp"], and running uvx windows-mcp manually also works fine.
However, Claude Desktop launches it as uv --directory <path> run windows-mcp instead of using uvx as specified in the manifest, and this fails specifically because of the path resolution under MSIX's virtualized AppData\Roaming.
Uninstalling/reinstalling Claude Desktop completely (including manual cleanup of AppData folders) did not fix the issue.

What Should Happen?

Claude Desktop appears to build the extension locally via uv --directory (editable build) rather than respecting the uvx/tool-run command specified in the extension manifest. This local build fails under the MSIX app's virtualized file system path.

Error Messages/Logs

Steps to Reproduce

Confirmed uv is correctly installed and in PATH
Manually running "C:\WINDOWS\system32\uv.exe" --directory "C:\Users\[user]\AppData\Local\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\Claude Extensions\ant.dir.cursortouch.windows-mcp" run windows-mcp works fine and starts the server successfully.
The extension's .mcp manifest specifies "command": "uvx", "args": ["windows-mcp"], and running uvx windows-mcp manually also works fine.
However, Claude Desktop launches it as uv --directory <path> run windows-mcp instead of using uvx as specified in the manifest, and this fails specifically because of the path resolution under MSIX's virtualized AppData\Roaming.
Uninstalling/reinstalling Claude Desktop completely (including manual cleanup of AppData folders) did not fix the issue.

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude Desktop: MSIX install (Claude_pzs8sxrjxfjjc)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

Claude Desktop appears to build the extension locally via uv --directory (editable build) rather than respecting the uvx/tool-run command specified in the extension manifest. This local build fails under the MSIX app's virtualized file system path.