pub fn profile_anchor(profile: &[NurbsCurve]) -> Result<ProfileAnchor, String>Expand description
Validate a closed planar profile loop and derive its placement anchor —
the path sweep’s §1 block, extracted bit-identically: 16 samples per curve,
closure at tolerance, Newell normal, boundary-sample-mean origin,
planarity at tolerance * 100, pu = np.perpendicular(), pv = np × pu.