Reject chamfer extensions beyond trimmed rim faces

crates/kernel/src/tests.rs

@@ -445,7 +445,8 @@ fn chamfer_sloped_basin_rim() {
     let result = chamfer(&basin, &[Vec3::new(50.0, 4.0, 30.0)], 2.0).unwrap();
     // The removed triangular section has area s² sin(phi)/2. Its length varies
     // linearly between the sloped end walls, so its centroid gives the mean length.
-    let drop = 2.0 / 1.64_f64.sqrt();
+    let wall_slope: f64 = (20.0 - 4.0) / (30.0 - 10.0); // horizontal run / vertical drop
+    let drop = 2.0 / (1.0 + wall_slope.powi(2)).sqrt();
     let removed = drop * (60.0 - drop / 3.0);
     let before = measure(&basin).unwrap();
     let after = measure(&result).unwrap();
@@ -458,6 +459,26 @@ fn chamfer_sloped_basin_rim() {
     assert!(mesh.contains(Vec3::new(50.0, 3.5, 28.0)));
 }
 
+#[test]
+fn chamfer_wider_than_sloped_basin_rim_is_refused() {
+    for (margin, distance) in [(1.0, 2.0), (1.0, 3.0), (0.5, 4.0), (1.0, 1.0)] {
+        let slab = box_solid(Vec3::ZERO, Vec3::new(100.0, 60.0, 30.0)).unwrap();
+        let rectangle = |x0, y0, x1, y1| Loop2::polygon(&[Vec2::new(x0, y0), Vec2::new(x1, y0), Vec2::new(x1, y1), Vec2::new(x0, y1)]);
+        let pocket =
+            loft(&[(Plane::XY.offset(30.0), rectangle(20.0, margin, 80.0, 50.0)), (Plane::XY.offset(10.0), rectangle(30.0, 20.0, 70.0, 40.0))])
+                .unwrap();
+        let basin = boolean(&slab, &pocket, BoolOp::Cut).unwrap().unwrap();
+        let before = measure(&basin).unwrap();
+        let error = chamfer(&basin, &[Vec3::new(50.0, margin, 30.0)], distance).unwrap_err();
+        assert!(error.to_string().contains("larger than the neighbouring faces"), "{margin}, {distance}: {error}");
+        assert_eq!(measure(&basin).unwrap().volume, before.volume);
+        // A smaller chamfer on the same thin rim is still supported.
+        let smaller = chamfer(&basin, &[Vec3::new(50.0, margin, 30.0)], margin * 0.5).unwrap();
+        assert!(smaller.validity().is_empty());
+        assert!(measure(&smaller).unwrap().volume < before.volume);
+    }
+}
+
 #[test]
 #[ignore]
 fn debug_chamfer_cut() {