[BUG] MSIX packaging causes two critical regressions: ERR_QUIC_PROTOCOL_ERROR blank screen and CoworkVMService ACL lockout

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?

Windows 11 Home 10.0.26200, Claude desktop app v1.11187.4 (Anthropic Download / MSIX)

Issue 1: App launches to blank white screen due to ERR_QUIC_PROTOCOL_ERROR
Description
The Claude desktop app displays a permanent blank white screen on launch. The main window never loads any content. No error dialog is shown to the user.

Root Cause
The app's Electron/Chromium instance attempts to load https://claude.ai/ using the QUIC protocol (HTTP/3 over UDP port 443). On some network configurations (routers, ISPs, or Windows Firewall rules that block or corrupt UDP/443), the QUIC handshake fails with error code -356 ERR_QUIC_PROTOCOL_ERROR. Chromium does not gracefully fall back to HTTP/2, leaving the window permanently white.

This is confirmed in the app log at:
%LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\logs\main.log

Failed to load URL: https://claude.ai/ { errorCode: -356, errorDescription: 'ERR_QUIC_PROTOCOL_ERROR' }
Error page detected: { href: 'chrome-error://chromewebdata/' }
The log also shows:

[buddy-ble] mainView not ready: Timed out waiting for mainView to become ready
Important: claude.ai loads correctly in Chrome and Edge on the same machine — the QUIC failure is specific to the Electron app's Chromium instance. The prior non-MSIX version of the app did not exhibit this behavior on the same network.

Workaround Required
The user must manually create a desktop shortcut (the MSIX version installs no shortcut) with the following target:

"C:\Program Files\WindowsApps\Claude_1.11187.4.0_x64__pzs8sxrjxfjjc\app\claude.exe" --disable-quic
Additionally, because the MSIX app enforces single-instance behavior, any stuck claude.exe process must first be killed via Task Manager before launching the shortcut — otherwise the new instance detects the existing one, exits early, and the flag is never applied.

What Should Happen?

The app should detect QUIC failure and fall back to HTTP/2 (TCP), the same way Chrome and Edge do. Alternatively, QUIC should be disabled by default or made configurable within the app's settings UI.

Error Messages/Logs

Steps to Reproduce

Install the app

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

v1.11187.4

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_