Claude Desktop MSIX launches Windows-MCP from nonexistent non-virtualized path

[chrisatmd]

Summary

Installing Windows-MCP from Claude Desktop’s Extensions directory on the Microsoft Store/MSIX version results in “MCP Server Disconnected.”

The managed extension is installed inside Claude’s MSIX-virtualized application-data directory, but Claude attempts to launch it from a nonexistent conventional %APPDATA% path.

Environment

• Windows
• Claude Desktop MSIX package: Claude 1.26832.0.0
• Claude executable: C:\Program Files\WindowsApps\Claude_1.26832.0.0_x64__pzs8sxrjxfjjc\app\Claude.exe
• Windows-MCP extension: ant.dir.cursortouch.windows-mcp
• Extension version: 0.7.2
• Python 3.13+ installed
• UV installed and working

Command generated by Claude

uv --directory C:\Users\chris\AppData\Roaming\Claude\Claude Extensions\ant.dir.cursortouch.windows-mcp run windows-mcp

Actual result

Running Claude’s command manually produces:

error: The system cannot find the path specified. (os error 3)

The directory passed by Claude does not exist:

C:\Users\chris\AppData\Roaming\Claude\Claude Extensions\ant.dir.cursortouch.windows-mcp

The extension is actually installed here:

C:\Users\chris\AppData\Local\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\Claude Extensions\ant.dir.cursortouch.windows-mcp

Expected behavior

The managed extension should launch using the actual MSIX-virtualized extension directory and an absolute executable path visible to the packaged Claude process.

Alternatively, automatic installation should be disabled for the MSIX build and users should be directed to the documented manual configuration using:

C:\Users\chris\.local\bin\uvx.exe

with arguments:

windows-mcp
serve

Additional information

The Windows-MCP README already documents that:

1. Claude Desktop MSIX virtualizes %APPDATA%.
2. Automatic installation from Claude Directory can fail because ${__dirname} resolves to the incorrect non-virtualized path.
3. Electron applications inside the MSIX sandbox may require full executable paths.

Reinstalling the managed extension produces the same invalid launch command. Can the extension manifest be changed to support Claude Desktop MSIX, or does this require a fix in Anthropic’s extension launcher?

[Jeomon]

@bryan-anthropic Can you please help us?

[MilkyWay008]

The os error 3 is MSIX path virtualization: Claude's Store build redirects %APPDATA% into C:\Users\chris\AppData\Local\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\... but the extension launcher still emits the old non-virtualized path, which doesn't exist. Skip the auto-install and add the server manually in claude_desktop_config.json using the absolute exe path (uvx.exe with windows-mcp serve args), MSIX needs full paths, the ${__dirname} trick resolves wrong in there. oh btw, I keep a portable Hermes OTG on USB for these Windows agent recovery moments, https://github.com/MilkyWay008/Hermes-OTG if you want to poke at it.