Surface bodies: Patch, Stitch, Trim and Thicken

Kernel (surfaces):
- Bodies with an open shell are surface bodies (Body::is_surface).
- patch_region: a planar patch of a sketch region. patch_edges: a planar
  patch filling a closed loop of a body's edges.
- copy_faces: faces copied out as a surface.
- stitch: sew surfaces along coinciding edges, turning faces to agree; the
  result is a solid when it closes.
- trim: cut a surface by a plane or face and keep one side.
- thicken: offset planar and circular-cylindrical faces along their
  normals (one side or symmetric) into a solid. Plane copies slide;
  cylinder copies scale about the axis, exact for NURBS circles. Free
  edges get ruled walls. Faces meeting at a sharp edge are refused.

Doc features Patch, Stitch, Thicken (with operations) and SurfaceTrim;
engine commands FusionSurfacePatchCommand, FusionSurfaceStitchCommand,
FusionSurfaceThickenCommand and FusionSurfaceTrimCommand.

Tests (volumes):
- A 10x10 patch thickened by 2 gives 200, also symmetric.
- Half a cylinder side thickened outward gives half a ring; both halves
  inward give the full ring.
- Six faces of a box stitched back give 6000; an open box with its top
  patched from the edges, stitched, gives 6000.
- Trim keeps 30 or 70 of 100.
- Engine: patch, trim, thicken gives 140.

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

crates/doc/src/assembly.rs

@@ -153,10 +153,15 @@ impl FeatureKind {
         let pt = |p: &mut Vec3| *p = apply_point(m, *p);
         let dir = |v: &mut Vec3| *v = apply_vector(m, *v);
         match self {
-            FeatureKind::Sketch { plane, .. }
-            | FeatureKind::ConstructionPlane { plane }
-            | FeatureKind::Split { plane, .. }
-            | FeatureKind::Mirror { plane, .. } => map_plane_ref(m, plane),
+            FeatureKind::Sketch { plane, .. } | FeatureKind::ConstructionPlane { plane } | FeatureKind::Mirror { plane, .. } => {
+                map_plane_ref(m, plane)
+            }
+            FeatureKind::Split { plane, tool, .. } => {
+                map_plane_ref(m, plane);
+                if let Some(t) = tool {
+                    pt(&mut t.point);
+                }
+            }
             FeatureKind::Revolve { axis: AxisRef::Line { origin, dir: d }, .. } => {
                 pt(origin);
                 dir(d);
@@ -252,8 +257,18 @@ impl FeatureKind {
             | FeatureKind::Emboss { .. }
             | FeatureKind::Rib { .. }
             | FeatureKind::Remove { .. }
+            | FeatureKind::Stitch { .. }
+            | FeatureKind::Thicken { .. }
             | FeatureKind::Import { .. }
             | FeatureKind::MeshImport { .. } => {}
+            FeatureKind::Patch { edges, .. } => edges.iter_mut().for_each(pt),
+            FeatureKind::SurfaceTrim { plane, tool, keep, .. } => {
+                map_plane_ref(m, plane);
+                if let Some(t) = tool {
+                    pt(&mut t.point);
+                }
+                pt(keep);
+            }
         }
     }
 }