true when the workspace switcher menu is open — controls the
badge’s open state.
on_select: [Callback<AppSection>]
Optional callback fired when the user clicks an enabled rail
item (M-TRAY.2 / AUT-251). The argument is the clicked item’s
AppSection. M-TRAY.4 (AUT-253) wires this in
crates/app-ui to drive the active-surface signal; the
storybook stories leave it None so SSR snapshots stay
identical to the pre-callback baseline. Disabled items never
fire the callback.