Function tri_tri_intersection 

pub fn tri_tri_intersection(t1: &[[f64; 3]; 3], t2: &[[f64; 3]; 3]) -> TriTri

Exact triangle–triangle intersection: the overlap of each triangle’s plane-interval along line L = [max(lo1,lo2), min(hi1,hi2)]. Handles clean crossings AND Touches (on-plane vertices/edges). Coplanar is deferred to coplanar.rs; a single shared point returns Point (no cut).