Function measure_edge_against_pcurve_image 

pub fn measure_edge_against_pcurve_image(
    surface: &NurbsSurface,
    pcurve: &NurbsCurve,
    edge: &EdgeRecord,
    forward: bool,
    band: f64,
) -> Result<MeasuredTolerance, String>

max_t ‖C_3d(t) − S(p(t))‖ — how far the edge’s own 3D curve sits from the locus its pcurve traces on surface, recorded against band.

This is the measurement that makes a general pcurve → 3D transfer trustworthy: the transfer’s whole claim is that the interpolated 3D curve reproduces the composed image, and this is that claim, measured rather than assumed. It is equally what an iso SHORTCUT owes: rim_welds.rs accepts an iso on a structural degree/knot match, and this is the geometric check that would replace it.

forward follows the coedge’s own sense, as in BrepSolid::validate.