Fix modelling regressions and reconcile WIP UI work

crates/kernel/src/splitface.rs

@@ -1208,7 +1208,7 @@ mod tests {
         let m0 = measure(&c).unwrap();
         let side = c.faces(0.01).unwrap().iter().position(|f| f.plane_normal.is_none()).unwrap();
         // A horizontal line seen from the front (XZ sketch) at z = 5, swept along y.
-        let xz = Plane::XZ;
+        let xz = Plane { y: Vec3::Z, ..Plane::XZ };
         let tool = SplitTool::Curves { plane: xz, curves: vec![vec![Seg2::Line { a: Vec2::new(-20.0, 5.0), b: Vec2::new(20.0, 5.0) }]] };
         let s = split_faces(&c, &[side], &tool).unwrap();
         let m = measure(&s).unwrap();