What
The layout component behind Claude Code's composer (the box where you type messages) gained a sidebarFill setting for its side panel. By default it behaves exactly as before, keeping the panel's background color filled in. When turned off, the background is left transparent instead.
Why
This is an internal option, not a user-facing setting, and the default keeps today's appearance unchanged. It gives the interface the ability to show the sidebar without a solid background in places that need it.
Names in the bundlesidebarFill