Function thicken_sheet_faces 

pub fn thicken_sheet_faces(
    faces: &[BrepSolid],
    thickness: f64,
    corners: OffsetCorners,
) -> Result<BrepSolid, KernelRefusal>

The sheet faces thickened by thickness along the faces’ normals (negative: against them), its open creases closed as corners says.

faces are sheets of one face or more (crate::face_from_surface, crate::face_from_surface_trimmed) that meet along common edges, their normals all on one side of the sheet. The result is one solid.

Refuses faces whose normals disagree across a crease, a crease that is not a straight line with constant normals where it opens toward the thickened side or closes tighter than a right angle, a corner of other than three open creases, and whatever the single-face thicken or the union refuses.