Remark: The slicing-event boundary

VII-F's particle-supported cellulation event is a geometric construction in its own declared family CheungVIIEF (Theorem thm:event). We do not import its cell counts or uniqueness conclusion into a three-dimensional spatial cellulation. Our operational events below lie in the regular part. Attaching that separate slicing event would require its full geometric data and a clock-and-record dictionary. A slicing event is not already an Enter event.