Under the hood
Internal UI validator adds hover and layout checks and clearer error messages for dialog rendering
What
Claude Code's internal check that validates what can be drawn on screen (used when rendering dialogs and overlays) now tracks additional context called 'hoverScope' and 'siblingBoxKeys', and rejects a Box component's hover.display setting when it's placed around a dialog. It also gives a clearer error message when a Button's properties are misused, and a friendlier error for an unrecognized UI element that now lists the valid element names.
Why
These are internal correctness checks for how Claude Code's own interface is built, but the improved error messages mean any related bug shows up as a much more useful message rather than a cryptic one.