···146146147147 // Lid centered on base midpoint (y=hh) so both halves align when flat
148148 // At 180°: y flips around pivot → lid centered at y=hh, same as base center
149149- const lidMid = hh; // base midpoint
149149+ const lidMid = -hh; // flips to +hh at 180° to match base midpoint
150150 const lidLocal = [
151151 [-hw, lidMid + lidThick / 2, gap], [hw, lidMid + lidThick / 2, gap],
152152 [hw, lidMid - lidThick / 2, gap], [-hw, lidMid - lidThick / 2, gap],