Lips on rounded, shelled rims: the band along the rim's edge is raised from the body's own faces (kernel::raise_band: the rim face split along the band's exact offset edge, the band's walls swept up from the walls below, a top), since a join can't merge walls that continue each other; grooves cut with a band reaching into the free side so no wall coincides; tests against the band's area times its height

Fixes #29

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RjGw4gA5ZvKrU8MQP6sBgT

crates/kernel/src/lib.rs

@@ -26,6 +26,7 @@ mod heal;
 mod helix;
 mod iges_in;
 mod iges_out;
+mod lip;
 mod loopblend;
 mod measure;
 mod meshbody;
@@ -56,6 +57,7 @@ pub use delete_face::delete_faces;
 pub use helix::{loft_to_point, sweep_helix, sweep_helix_mesh};
 pub use iges_in::{MAX_IGES_BYTES, iges_import, iges_to_step};
 pub use iges_out::iges_export_bodies;
+pub use lip::raise_band;
 pub use measure::{BodyMeasure, measure};
 pub use meshbody::{MAX_TRIANGLES, mesh_body};
 pub use offset::with_same_surface;