/desktop (and /app) fails on Windows when Claude Desktop is the MSIX package: "Failed to open Claude Desktop"

Summary

/desktop (and its alias /app) always fails with "Failed to open Claude Desktop. Please try opening it manually." on Windows, even when Claude Desktop is installed, running, and signed in. The cause appears to be that /desktop tries to launch the standalone Desktop build, but current Claude Desktop for Windows ships only as an MSIX/AppX package, which has no standalone executable at the path /desktop looks for.

Environment

• Claude Code CLI: v2.1.178
• OS: Windows 11 Pro (build 10.0.22631)
• Claude Desktop: MSIX/AppX package Claude_1.13576.0.0_x64__pzs8sxrjxfjjc in C:\Program Files\WindowsApps\... — running, signed in, on a Claude subscription
• /rc (remote control) works fine; only /desktop fails

What happens

Running /desktop immediately prints:

Failed to open Claude Desktop. Please try opening it manually.

...even though Desktop is installed, running, and signed in — none of the documented failure conditions apply.

Root cause (from investigation)

• The Claude Code binary contains the string AnthropicClaude immediately adjacent to the "Failed to open Claude Desktop" string, indicating /desktop looks for the standalone build at %LOCALAPPDATA%\AnthropicClaude\Claude.exe.
• Current Claude Desktop for Windows — both the Microsoft Store install and the claude.com web installer — installs as an MSIX/AppX package (verified via Get-AppxPackage Claude: SignatureKind: Store for the Store build, Developer for the web installer). There is no %LOCALAPPDATA%\AnthropicClaude\Claude.exe and no %LOCALAPPDATA%\Programs\claude. The app lives in protected WindowsApps and is launchable only via its AppUserModelID (Claude_pzs8sxrjxfjjc!Claude) or the claude:// URI protocol.
• So /desktop's launcher cannot locate/launch the MSIX Desktop, producing "Failed to open."

Reproduction

1. On Windows, install Claude Desktop via the Microsoft Store or the claude.com web installer (both produce an MSIX package; no standalone .exe build is shipped anymore).
2. In Claude Code (CLI), run /desktop (or /app).
3. Observe: "Failed to open Claude Desktop. Please try opening it manually." — even with Desktop installed, running, and signed in.

Evidence / confirms the diagnosis

• explorer.exe shell:AppsFolder\Claude_pzs8sxrjxfjjc!Claude launches the MSIX Desktop correctly.
• After clearing a stale HKCU\Software\Classes\claude orphan key (which had URL Protocol but no shell\open\command), the claude:// protocol resolves to the MSIX app via its package-declared handler.

Suggested fix

When the standalone AnthropicClaude\Claude.exe path is absent, have /desktop launch Desktop via its AppUserModelID (shell:AppsFolder\<AUMID>) or the claude:// protocol, so it works with the MSIX/Store-packaged Desktop (now the only Windows distribution).