STEP: reader

Own ISO 10303-21 parser and AP203/AP214/AP242 geometry reader in the kernel
(step_import): planes, cylinders, cones, spheres, tori, B-spline and rational
surfaces, surfaces of revolution/extrusion; lines, conics, B-spline curves;
breps with voids, faceted breps, shell models; units (SI prefixes, conversion
based), product names, colours, assemblies (NAUO + item-defined
transformations, mapped items). Hostile input is capped and guarded; faces
that cannot be read are left out and reported. Faces that wrap around a
closed non-periodic direction (pipe tori, revolved B-spline bands) are split
for truck's mesher. Bodies are meshed per shell so open imports never panic.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/kernel/src/lib.rs

@@ -2,7 +2,7 @@
 //!
 //! Everything SolveCraft does with solids goes through this crate: building bodies from planar
 //! regions (extrude, revolve) and primitives, booleans, fillets and chamfers, tessellation,
-//! measurement and STEP export. The implementation uses the `truck` crates (Apache-2.0; see
+//! measurement and STEP export and import. The implementation uses the `truck` crates (Apache-2.0; see
 //! `plan/adr/0001-geometry-kernel.md`) plus our own local operations (edge fillets and
 //! chamfers in `blend.rs`), but no truck type appears in the public API, so the kernel can be
 //! replaced without touching the rest of the workspace.
@@ -20,6 +20,7 @@ mod ops;
 mod polybool;
 mod polyhedron;
 mod step;
+mod step_in;
 mod topo;
 
 pub use blend::{chamfer, fillet};
@@ -30,6 +31,7 @@ pub use ops::{BoolOp, boolean, split_by_plane, transform, transform_matrix};
 pub use polybool::planar_boolean;
 pub use polyhedron::{HalfSpace, convex_polyhedron, draft, shell};
 pub use step::step_export;
+pub use step_in::{ImportedBody, StepImport, StepNode, step_import};
 pub use topo::{TopoCounts, merged_topology, seam_flags};
 
 #[derive(Debug, Clone, PartialEq, thiserror::Error)]