Desktop Extension Install button does nothing for "Affinity by Canva" (MSIX build, Windows)

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 Install button for the directory desktop extension "Affinity by Canva" does nothing — no install, no error, no UI change. Web/cloud connectors install normally on the same machine (e.g. "Affinity" the CRM, a Web connector, adds with no problem), so the failure is specific to desktop extensions / local MCP servers.

No new mcp-related log file is created in %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\Logs\ when Install is clicked — the extension install is never even attempted.

What Should Happen?

The desktop extension installs successfully and the Affinity MCP server appears under connected local "Desktop" servers in Claude Desktop.

Error Messages/Logs

No error output visible. No new log file is created in %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\Logs\ when Install is clicked. The install is silently ignored.

Build info:
- Build: MSIX, Claude_1.12603.1.0_x64__pzs8sxrjxfjjc
- SignatureKind: Developer, Status: Ok
- Install path: C:\Program Files\WindowsApps\Claude_1.12603.1.0_x64__pzs8sxrjxfjjc

Steps to Reproduce

1. Org settings → Connectors: desktop extension allowlist is ON, "Affinity" (Type: Desktop) is added to the allowlist.
2. Affinity app: Settings → Model Context Protocol → "Enable Affinity MCP" is ON, all permissions enabled, app running.
3. In Claude Desktop, click Install on the "Affinity by Canva" desktop extension (directory page and via the in-app connectors view).
4. Nothing happens. Repeated many times, including after a full quit/relaunch and a clean uninstall/reinstall.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Pre-MSIX standalone build (worked on separate machine)

Claude Code Version

Claude_1.12603.1.0_x64__pzs8sxrjxfjjc (MSIX/WindowsApps build)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Non-interactive/CI environment

Additional Information

Note: This issue is for Claude Desktop (not Claude Code CLI), but filing here as it is the primary issue tracker.

Environment:

• OS: Windows; user is local admin
• Plan: Team (user is org Owner)
• Build: MSIX, Claude_1.12603.1.0_x64__pzs8sxrjxfjjc (installed via claude.com/download)

Ruled out:

• No isDesktopExtensionEnabled / isDesktopExtensionDirectoryEnabled policy keys present in HKLM or HKCU (searched registry).
• Org-level desktop extension allowlist is ON and Affinity is listed.
• Affinity-side MCP server is enabled and the app is running.
• Clean uninstall (Get-AppxPackage -Name Claude | Remove-AppxPackage) + reinstall → same version, same behavior.
• No new mcp-related log file is created in %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\Logs\ when Install is clicked.
• claude_desktop_config.json contains no mcpServers block; manual JSON editing is reportedly ignored on MSIX builds.

Likely cause:
Known MSIX/Microsoft Store packaging issue where local MCP servers / desktop extensions are silently ignored. The same connector installs and works on a separate machine running an older standalone (pre-MSIX) build.