OptionalcellOptional: map a cell rect + the dragged pose to the new pose. Default
writes { x, y, width, height } into the dragged pose (assumes
RectPose). Override for point-only poses or other shapes. The
dragged argument is the pre-drop pose of the child being placed —
use it to preserve fields the cell rect doesn't carry (e.g. rotation,
domain metadata).
Gap between cells, in world units. Default 0.