Return bare face from BuildFace::triangle

This gives the caller more flexibility on what to do with it.

crates/fj-kernel/src/operations/build/face.rs

@@ -18,7 +18,7 @@ pub trait BuildFace {
         points: [impl Into<Point<3>>; 3],
         edges: [Option<Handle<GlobalEdge>>; 3],
         objects: &mut Service<Objects>,
-    ) -> (Handle<Face>, [Handle<GlobalEdge>; 3]) {
+    ) -> (Face, [Handle<GlobalEdge>; 3]) {
         let [a, b, c] = points.map(Into::into);
 
         let surface = Surface::plane_from_points([a, b, c]).insert(objects);
@@ -46,7 +46,7 @@ pub trait BuildFace {
             (cycle, global_edges)
         };
 
-        let face = Face::new(surface, exterior, [], None).insert(objects);
+        let face = Face::new(surface, exterior, [], None);
 
         (face, global_edges)
     }

crates/fj-kernel/src/operations/build/shell.rs

@@ -2,6 +2,7 @@ use fj_math::Point;
 
 use crate::{
     objects::{Face, Objects, Shell},
+    operations::Insert,
     services::Service,
 };
 
@@ -25,7 +26,8 @@ pub trait BuildShell {
         let (side_c, _) =
             Face::triangle([b, c, d], [Some(bc), Some(dc), Some(bd)], objects);
 
-        let faces = [base, side_a, side_b, side_c];
+        let faces =
+            [base, side_a, side_b, side_c].map(|face| face.insert(objects));
         Shell::new(faces)
     }
 }