[BUG] Internal browser crashes entire app when clicking login button (Supabase Auth)

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 internal browser in Claude Desktop crashes and closes the entire app immediately when clicking a "Sign in" / login button on a third-party web app that uses Supabase Auth. The page itself loads and renders fine — the crash happens specifically on the login button click, not on page load.

This started right after a manual app update. The exact same site and login flow worked with zero issues in the internal browser the day before, with no changes made to the site itself. The same login works perfectly in a regular external Chrome/Edge browser.

What Should Happen?

Clicking the "Sign in" button should either complete the login successfully or fail gracefully (e.g. show an error message), without crashing or closing the Claude Desktop app.

Error Messages/Logs

No error message is shown in the UI. The app closes/crashes immediately on click — no visible error dialog or console output was captured.

Steps to Reproduce

1. Open Claude Desktop, go to the Code tab
2. Start a new session (no project folder needs to be connected)
3. Ask Claude to open the internal browser at a URL that has an email/password login form backed by Supabase Auth (e.g. any Supabase Auth-powered login page)
4. Page loads normally, form renders correctly
5. Click the "Sign in" / login submit button (with valid email + password entered)
6. Claude Desktop crashes and closes immediately

Note: the exact same login flow works with zero issues when opened in a regular external browser (Chrome/Edge).

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Unknown exact version — was working the day before a manual in-app update was applied. No version number was recorded before updating.

Claude Code Version

2.1.218 (Claude Code)

Platform

Other

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

This appears to be specific to the internal browser's handling of Supabase Auth login flows (possibly related to popup/redirect handling or session storage APIs in the embedded webview). Happy to provide the site URL privately if needed for reproduction, as it's an app currently in private testing.