[BUG] Claude Desktop (Windows MSIX 1.21459.0.0): Settings > Extensions stuck on "Loading extensions..." indefinitely

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?

Opening Settings > Desktop app > Extensions shows "Loading extensions..." forever. The page never renders. Reproduced on two independent Windows 11 machines, same build (1.21459.0.0, Microsoft Store/MSIX package Claude_pzs8sxrjxfjjc), same account (Max plan).

Evidence it is a renderer/UI issue, not backend: main.log shows extension enumeration completing successfully every launch ("can_install check completed: 3 extensions checked", all canInstall: true, no errors). extensions-installations.json and extensions-blocklist.json are valid JSON; blocklist fetch succeeds. All 3 installed extensions (Filesystem 0.2.3, Desktop Commander 0.2.44, ElevenLabs Agents 1.0.0) load and their MCP tools work normally in conversations. Only the management page is broken.

What Should Happen?

The Extensions settings page should render the installed extension list that the main process already enumerated successfully.

Error Messages/Logs

main.log (repeats identically on every launch, no errors):
  processing extension registry entries
  can_install check completed: 3 extensions checked (all canInstall: true)
No errors in claude.ai-web.log or unknown-window.log at the moment the page hangs.

Steps to Reproduce

1. Claude Desktop 1.21459.0.0 from Microsoft Store on Windows 11 (MSIX package Claude_pzs8sxrjxfjjc), with one or more extensions installed (reproduced with Filesystem, Desktop Commander, ElevenLabs Agents).
2. Open Settings > Desktop app > Extensions.
3. Page shows "Loading extensions..." and never renders (waited 10+ minutes). Reproduced across restarts, cache clears, full web-state reset, and on two different machines.

Claude Model

_No response_

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude Desktop 1.21459.0.0 (Windows MSIX / Microsoft Store)

Platform

Other

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

Already tried, no effect: full process kill + relaunch; clearing Cache/Code Cache/GPUCache/Dawn caches; full web-state reset (IndexedDB, Local Storage, Session Storage, WebStorage, Preferences, shared_proto_db) - backend still enumerates fine, page still hangs; network verified fine; no app update available.

Not a duplicate of #67919 (extension install hang) - this is the Extensions settings page never rendering at all. Extensions themselves work normally; only the management UI is affected. This is a Claude Desktop app issue (no CLI involved).