[BUG] New web session at claude.ai/code always creates two duplicate sessions in sidebar

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?

When creating a new session on claude.ai/code (Claude Code on the web), two identical sessions always appear simultaneously in the sidebar. This happens every single time without exception.

What Should Happen?

Creating a new session should result in exactly one session appearing in the sidebar.

Error Messages/Logs

No error messages displayed. The duplicate session appears silently.

Steps to Reproduce

1. Go to claude.ai/code
2. Select a repository and create a new session
3. Wait for the container to start
4. Check the sidebar — two sessions are listed instead of one

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

N/A (web interface at claude.ai/code, not CLI)

Platform

Other

Operating System

Windows

Terminal/Shell

Other

Additional Information

• 100% reproducible on every session creation
• Tested in multiple browsers (Chrome, etc.) — same result
• Cleared cache/cookies for claude.ai — same result
• Disabled all browser extensions — same result
• The duplicate session can be manually deleted/archived, but the issue recurs on every new session creation