No panics in the boolean's final assembly (the web build aborts on any panic: the Plastic Enclosure sample panicked 8 times and crashed the browser's start page); face pushes check their result and fall back to the general offset (a boss standing on a plate joins again with off-axis cylinder seams); offset errors name the face they can't move; docs/robustness.md with the before and after rates; caught panics counted per design in the robustness runs

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/kernel/src/coplanar.rs

@@ -42,8 +42,11 @@ fn planes(b: &Body) -> Vec<(usize, PlaneFace)> {
 
 /// Push the planar faces of `b` lying in the plane (n, d) — n their outward normal — along n
 /// by `delta` (negative: inward). Their neighbours must stand perpendicular to the plane.
-fn push_faces(b: &Body, n: Vec3, d: f64, delta: f64) -> Result<Body> {
-    match push_faces_exact(b, n, d, delta) {
+pub(crate) fn push_faces(b: &Body, n: Vec3, d: f64, delta: f64) -> Result<Body> {
+    // The exact rebuild, unless it came out unsound (a curved side it couldn't re-sweep).
+    match push_faces_exact(b, n, d, delta)
+        .and_then(|r| if r.validity().is_empty() { Ok(r) } else { Err(KernelError::Failed("pushing a face: an unsound result".into())) })
+    {
         Ok(r) => Ok(r),
         // Faces of planes and cylinders: every face follows (any neighbours).
         Err(e) => {
@@ -66,7 +69,7 @@ fn push_faces(b: &Body, n: Vec3, d: f64, delta: f64) -> Result<Body> {
     }
 }
 
-fn push_faces_exact(b: &Body, n: Vec3, d: f64, delta: f64) -> Result<Body> {
+pub(crate) fn push_faces_exact(b: &Body, n: Vec3, d: f64, delta: f64) -> Result<Body> {
     let size = b.size();
     let tol = (size * 1e-7).max(1e-9);
     let fail = |m: &str| KernelError::Failed(format!("pushing a face: {m}"));

crates/kernel/src/offset.rs

@@ -68,7 +68,7 @@ impl Surf {
     fn grad(&self, p: Vec3) -> Option<Vec3> {
         match *self {
             Surf::Plane { n, .. } => Some(n),
-            Surf::Cylinder { convex, .. } | Surf::Sphere { convex, .. } | Surf::Cone { convex, .. } => {
+            Surf::Cylinder { convex, .. } | Surf::Sphere { convex, .. } | Surf::Cone { convex, .. } | Surf::Torus { convex, .. } => {
                 self.normal(p).map(|n| if convex { n } else { -n })
             }
         }
@@ -454,7 +454,13 @@ pub(crate) fn offset_body(b: &Body, shift: impl Fn(usize, Vec3) -> f64) -> Resul
     let mut new = Vec::with_capacity(faces.len());
     let mut shifts = Vec::with_capacity(faces.len());
     for (i, f) in faces.iter().enumerate() {
-        let sf = surf_of(f, tol * 100.0).ok_or_else(|| fail("only bodies with planes, cylinders, cones, spheres and tori"))?;
+        let sf = surf_of(f, tol * 100.0).ok_or_else(|| {
+            let at = samples(f).first().map(|(p, _)| format!(" (a face at [{:.2}, {:.2}, {:.2}])", p.x, p.y, p.z)).unwrap_or_default();
+            if std::env::var("DBG_OFFSET").is_ok() {
+                eprintln!("unrecognised face: {:?}", f.surface());
+            }
+            fail(&format!("only bodies with planes, cylinders, cones, spheres and tori{at}"))
+        })?;
         let n = match sf {
             Surf::Plane { n, .. } => n,
             Surf::Cylinder { a, .. } | Surf::Cone { a, .. } | Surf::Torus { a, .. } => a.any_perp(),

crates/kernel/src/splitface.rs

@@ -1230,7 +1230,8 @@ mod tests {
         let mut tops: Vec<f64> = s.faces(0.01).unwrap().iter().filter(|f| (f.centroid.z - 20.0).abs() < 1e-6).map(|f| f.area).collect();
         tops.sort_by(f64::total_cmp);
         let pi = std::f64::consts::PI;
-        assert!(rel(tops[0], pi * 16.0) < 1e-3 && rel(tops[1], pi * 84.0) < 1e-3, "{tops:?}");
+        // (Face areas come from meshes: within their sag, which depends on where seams lie.)
+        assert!(rel(tops[0], pi * 16.0) < 2e-3 && rel(tops[1], pi * 84.0) < 2e-3, "{tops:?}");
     }
 
     /// A plane through a hole in a plate's top: the top splits in two, each piece holding