Record a region loft section as its boundary curve

A lofted surface's region cross sections are recorded as the curve round
each region, as the reference records them; a region recorded as a
region made the reference refuse to open the drawing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scene/model/loft_command_model.rs

@@ -9,7 +9,9 @@ use super::sweep_model::embedded_path;
 
 pub(crate) fn embedded_section(entity: &EntityType) -> Option<EmbeddedEntity> {
     match entity {
-        EntityType::Region(region) => Some(EmbeddedEntity::Region(region.clone())),
+        // A region as the curve round it, as the reference records it.
+        EntityType::Region(region) => Some(super::sweep_model::region_boundary_entity(entity)
+            .map_or_else(|| EmbeddedEntity::Region(region.clone()), |(curve, _)| curve)),
         EntityType::Point(point) => Some(EmbeddedEntity::Point(point.clone())),
         _ => embedded_path(entity),
     }