Class ClashSession

Ingest N elements from flat arenas.

• positions: concatenated per-element vertex coords (x,y,z,...)
• pos_ranges: 2 per element = [float_offset, float_len]
• indices: concatenated per-element LOCAL (0-based) triangle indices
• idx_ranges: 2 per element = [idx_offset, idx_len]
• aabbs: 6 per element = [minx,miny,minz,maxx,maxy,maxz]

Run one rule. group_a/group_b are GLOBAL element indices. OMIT group_b (pass undefined/null) for a self-clash within group_a; pass an array -- INCLUDING an empty one -- for a two-sided rule. An empty array is a B side that matched nothing and yields no clashes, which is why this is nullable rather than "empty means self" (#5354). mode: 0 = hard, 1 = clearance. Records carry GLOBAL element indices.