Group API

React Group props, callbacks, geometry, and forwarded ref.

GroupProps combines node geometry and resize props with title, headerContent, canContain, groupCallbacks, and membership/commit convenience callbacks.

The forwarded ref is the GroupNodeMirror. The group renders a pointer-transparent body, an interactive header, and visual resize cues backed by core collision handles.

Geometry changes resynchronize after mount. Callback props remain current across renders and are composed with callbacks already present on a supplied core object.