nx_bvh_test.nx

nx_bvh_test.nx -- exercise BVH build on tetrahedron mesh in both single-leaf and forced-multi-node configurations. Closed-form invariants: (a) Default-threshold build on tetrahedron (4 tris, threshold=4) yields exactly 1 node (a single leaf with count=4). (b) Root AABB matches mesh bbox: (0,0,0) to (EDGE,EDGE,EDGE). (c) Sum of leaf counts == n_tris. (d) leaf_threshold=2 forces the tetrahedron to split, producing >= 3 nodes (1 internal + 2 leaves minimum) and a tree where sum of leaf counts is still 4. (e) Internal node's right child index == left + 1 (depth-first sibling-adjacency invariant). (f) Empty mesh degenerate: n_tris=0 returns BVH with n_tris=0. expect_exit: 0 license_tier: ORIGINAL