overlay property
Builder for an optional consumer-provided overlay rendered above
the displayed origin and Stage's own overlay/scrim. Use it to add
mode-aware UI (e.g., a crop tool's appbar). Read Stage.of to
inspect displayConfig() and decide what to render. The builder
is invoked on every Stage rebuild — consumer owns any animations
(e.g. AnimatedSwitcher / AnimatedOpacity) around its output.
Implementation
final WidgetBuilder? overlay;