Function offset_face_carrier_measured 

pub fn offset_face_carrier_measured(
    solid: &BrepSolid,
    face_id: u64,
    distance: f64,
    planar_extension: f64,
) -> Result<OffsetFaceCarrier, String>

offset_face_carrier, with every entity it builds measured against the deviation it was meant to reproduce.

The carrier is bit-identical to offset_face_carrier’s — same body, same arithmetic, in the same order — with a read-only measurement pass appended. Three quantities land in CarrierDeviation:

• the carrier SURFACE’s fit against the pointwise offset it interpolates (offset_surface_measured);
• each carrier EDGE’s 3D curve against the locus its pcurve traces on that surface — the trim boundary is built by sampling exactly that composition and interpolating the images, so this is the construction’s own claim, measured rather than assumed;
• each carrier VERTEX, propagated from the incident edge ends.

The interesting output is CarrierDeviation::exceedances: an entity whose measured deviation is worse than the size-derived band assumed. That is a construction that went wrong in a way the derived band alone cannot see, and it is the case a caller should refuse on rather than ship.