Complete exact INTERSECT behavior

src/scene/convert/solid3d_tess.rs

@@ -159,6 +159,10 @@ pub fn kernel_body(solid: &Solid3D) -> Option<KernelBody> {
     kernel_acis_body(&solid.acis_data)
 }
 
+pub fn kernel_region_body(region: &Region) -> Option<KernelBody> {
+    kernel_acis_body(&region.acis_data)
+}
+
 pub fn kernel_surface_body(surface: &Surface) -> Option<KernelBody> {
     kernel_acis_body(&surface.acis_data)
 }

src/scene/entity.rs

@@ -602,6 +602,9 @@ impl Scene {
                     Some(EntityType::Solid3D(solid)) => {
                         crate::scene::convert::solid3d_tess::kernel_body(solid)
                     }
+                    Some(EntityType::Region(region)) => {
+                        crate::scene::convert::solid3d_tess::kernel_region_body(region)
+                    }
                     Some(EntityType::Surface(surface)) => {
                         crate::scene::convert::solid3d_tess::kernel_surface_body(surface)
                     }

src/scene/model/solid_model.rs

@@ -365,13 +365,18 @@ pub enum Bool {
 /// missing, and passing that on unchanged is the point: a half-done boolean
 /// looks finished.
 pub fn boolean(op: Bool, a: &Body, b: &Body) -> Option<Body> {
+    boolean_result(op, a, b).ok()
+}
+
+/// Combine two solids while retaining the kernel's exact refusal reason.
+pub fn boolean_result(op: Bool, a: &Body, b: &Body) -> Result<Body, brep::Snag> {
     let how = match op {
         Bool::Union => brep::Operation::Union,
         Bool::Subtract => brep::Operation::Difference,
         Bool::Intersect => brep::Operation::Intersection,
     };
     let tolerance = brep::operation_tolerance(&[a, b]);
-    brep::combine(a.clone(), b.clone(), how, tolerance).ok()
+    brep::combine(a.clone(), b.clone(), how, tolerance)
 }
 
 // ── Tessellation ────────────────────────────────────────────────────────────