[BUG] Docked pane close mark (×) jumps on hover (terminal, fullscreen)

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?

In the fullscreen terminal layout, hovering over the close mark (×) in a docked pane's top-right corner moves the mark out of place. It happens with the built-in /diff pane and with a mod's pane opened through $.ui.open.

What Should Happen?

The × should stay where it is on hover and only change its colour or highlight, so it can be clicked reliably.

Error Messages/Logs

None. It's a visual problem.

Steps to Reproduce

1. Run Claude Code in Ghostty inside tmux (TERM=tmux-256color, 24-bit colour passed through), fullscreen layout.
2. Make the terminal wide enough for panes to dock beside the conversation.
3. Run /diff, or open any mod pane.
4. Move the mouse over the × in the pane's top-right corner.
5. The × moves when the pointer reaches it.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.295 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

Ghostty inside tmux (TERM=tmux-256color), zsh

Theme: a custom theme based on dark-ansi. Related issue: #98987, about the × being kept one column in from the terminal's edge, fixed in 2.1.289. That one was about position; this one is about hover.