Panel rail
The activity rail — which panels are open, drawn as icons on the edge they open on.
A ShellAside with a ToggleGroup inside it. Both halves matter, and the rail is the case that
shows why: it was a bare ToggleGroup standing in for the region, and a ToggleGroup is a
control, so its recipe carries w-fit and rounded-lg. Used as a region it brought its 8px
radius with it, and the rail's top corner curled away from the header's border and left a step
that read as a second border. Setting rounded-none on it would have hidden that; giving the
region to the component whose job it is fixes it.
multiple, because the panels are independent. The workspace showcase runs the same machine with
multiple={false}, where exactly one panel shows at a time.
Where it comes from
import { PanelRail, type RailPanel } from "@/showcases/shared";docs/showcases/shared/index.tsx. It is not published, and it is not on its way to being — see
Blocks for the line.