[BUG] Desktop: scrolling does nothing over a `Client` region in a plugin pane

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separately for multiple bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

In the desktop app, a plugin pane doesn't scroll while the pointer is over a Client element. Over the pane's Box and Text content, scrolling works.

The Client in my pane is a tab bar, 3 rows tall, at the top of a pane whose content is taller than the pane. With the pointer over the tab bar, the pane stays put. With the pointer on the rows below, the pane scrolls.

So a list drawn in a Client wouldn't scroll either, and a plugin has to keep scrollable content in native elements.

What Should Happen?

Scrolling over a Client should scroll the pane that holds it, as it does over Box and Text. A Client that wants wheel input for itself could receive it as a pointer event and opt in to handling it, with the pane scrolling otherwise.

Error Messages/Logs

None. The Client still gets down, move, enter and leave pointer events.

Steps to Reproduce

1. In a plugin, draw a Pane whose content is taller than the pane, with a Client of a few rows at the top. Mine draws a row of Box tabs and handles onPointer.
2. Open the plugin's pane in a Code-mode session in the Claude desktop app, docked so its content overflows.
3. Put the pointer over the rows below the Client and scroll. The pane scrolls.
4. Put the pointer over the Client and scroll. The pane doesn't move.

Claude Model

Not model-related.

Is this a regression?

Don't know.

Claude Code Version

2.1.295 (the engine the desktop app runs), Claude desktop app 2.31226.1

The CLI is on 2.1.296. I haven't tested 2.1.296 in the desktop app.

Platform

Anthropic API

Operating System

macOS 15.7.3

Terminal/Shell

Claude desktop app (Code mode)

Additional Information

Related: #100890 asks for a tab group element. A Client works as a tab bar today, which is how this came up.