0.3.8d2 test: clean retry from 0.3.8c. Wall v2 changes actual rendered geometry AND all audited wall-height snap elevations from 2 SU to 1 SU. preserves confirmed 0.3.7n and adds screen-space snap competition for ceilings. Wall Top/Bottom and Ceiling Edge remain legal targets; finger proximity chooses intent, with a small tie margin protecting Ceiling → Ceiling continuation in crowded structures.