Function intersect_plane_torus 

pub fn intersect_plane_torus(
    torus: &ToroidalSurface,
    normal: Vec3,
    d: f64,
) -> Result<Vec<IntersectionCurve>, MathError>

Intersect a plane with a toroidal surface.

The torus-plane intersection is a degree-4 curve with no simple closed form. Uses grid sampling with sign-change detection and Newton refinement.

Errors

Returns an error if curve fitting fails.