The groove's facets came in sweep order, and the BSP takes each list's first
polygon as its splitter, so the tree was as deep as the list: quadratic time and
memory. An M8 x 60 mm thread ran out of tree depth after 12.9 GB. A fixed shuffle
gives a shallow tree and the same result (volume and faces equal to 1e-9).
Co-authored-by: Claude Opus 5.5 <[email protected]>
