Chunks keep the player's bytes apart from the composed density: plan
presses land in an owner-keyed PlanTerrainPatch that is retracted with
its feature and never touches history, so removing a railway takes its
bed with it and a human fill under it survives. Surface queries answer
Surface | Hole | Outside instead of pretending the heightfield continues
over a hole or past the border; landforms issued inside a plan eval are
plan, outside it history. Seven tests pin the layering, including
same-inputs-twice equality.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
