ReadonlycenterCentre in world space, copied.
ReadonlyextentsHalf-extents in world units — the box spans center ± extents. Every
component finite and > 0. (Half, not full, so a cube of side 2 is
(1, 1, 1); that matches how §22's box collider is authored.)
Optional ReadonlyfalloffWidth of the inward edge fade in world units, applied per axis, default 0.
Finite and >= 0.
Readonlyshape
An axis-aligned box for volumeField. Rotated boxes are staged: they need an inverse transform per sample, and §27 asks for volume inclusion, not for a transform hierarchy.