[BUG] White space between sidebar and chat area after app update (macOS)

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?

After updating the Claude desktop app, a large white space appeared between the sidebar and the chat area.
Steps to reproduce: Update the app
What I tried:

Restarted the app
Resized the window
Cleared cache (both via terminal and Help menu)
Reset App Data
Reinstalled the app

None of the above fixed the issue.
OS: macOS (13.4)
App version: Claude 1.2581.0 (f10398)

<img width="757" height="680" alt="Image" src="https://github.com/user-attachments/assets/653e7816-450b-46b4-9d8d-5549bb5c3462" />

What Should Happen?

The sidebar and chat area should be displayed side by side with no gap between them, as it was before the update.

Error Messages/Logs

No error messages displayed. The issue is a visual/layout bug only.

Steps to Reproduce

1. Update the Claude desktop app to the latest version
2. Launch the app
3. A large white space appears between the sidebar and the chat area

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Unknown

Claude Code Version

Claude 1.2581.0 (f10398)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_