Replace the face/back boolean with a three-state facing (face, back,
standing) seeded from setup placements. Parts now orient about the
anchor at the resting face/edge, so back-down parts sit on the table
instead of below it and standing parts rest on their bottom edge.
Replace the path->part-list store with a per-part map keyed by part id, so each placed part carries its path, stack index, and face. Derive each path's ordered children for stacking, and flip face-down parts in PartPlacement.
Apply the same tilt to every stacked part and rotate it about its local
Y axis instead of Z. Default tilt to 1 degree when a stacking strategy
is present, and arc the poker deck along the surface's bottom edge.
Replace the per-part lift with a local Y-axis tilt that fans the stack,
and add zStart/zEnd to ramp the stack's height across the curve so it
arches in 3D. Update the poker deck and docs accordingly.
hypercross