diff --git a/crates/engine/src/boolean_regression_tests.rs b/crates/engine/src/boolean_regression_tests.rs
new file mode 100644
index 00000000..4db35a63
--- /dev/null
+++ b/crates/engine/src/boolean_regression_tests.rs
@@ -0,0 +1,34 @@
+//! Booleans that failed, panicked or hung, replayed from the scripts in
+//! `examples/regressions/` (each script's description says what went wrong).
+
+use serde_json::Value;
+
+use crate::Session;
+
+fn replay(script: &str) -> Session {
+    let mut s = Session::default();
+    let script: Value = serde_json::from_str(script).unwrap();
+    s.run_script(&script).unwrap();
+    s
+}
+
+fn volume(s: &Session, body: &str) -> f64 {
+    s.model.state().body(body).map(|b| solvecraft_kernel::measure(&b.body).unwrap().volume).unwrap_or(0.0)
+}
+
+/// Slab less a 557.68 × 100 × 120 pocket and the loft below its floor (556.68 × 99 down 4 mm to
+/// 80 × 80; prismatoid: h/6 · (A_top + A_bottom + 4 A_mid)).
+fn slab_pocket_loft() -> (f64, f64) {
+    let slab = 900.0 * 480.0 * 160.0;
+    let loft = 4.0 / 6.0 * (556.68 * 99.0 + 80.0 * 80.0 + 4.0 * (556.68 + 80.0) / 2.0 * (99.0 + 80.0) / 2.0);
+    (slab - 557.68 * 100.0 * 120.0, loft)
+}
+
+#[test]
+fn shallow_loft_cut_from_the_top_face() {
+    let s = replay(include_str!("../../../examples/regressions/shallow_loft_cut_from_top_face.json"));
+    let (_, loft) = slab_pocket_loft();
+    let want = 900.0 * 480.0 * 160.0 - loft;
+    let got = volume(&s, "Body1");
+    assert!((got - want).abs() < 1e-9 * want, "{got} vs {want}");
+}
diff --git a/crates/engine/src/lib.rs b/crates/engine/src/lib.rs
index 22a5106f..beb357bb 100644
--- a/crates/engine/src/lib.rs
+++ b/crates/engine/src/lib.rs
@@ -503,6 +503,8 @@ impl Session {
     }
 }
 
+#[cfg(test)]
+mod boolean_regression_tests;
 #[cfg(test)]
 mod construct_tests;
 #[cfg(test)]
diff --git a/crates/kernel/src/heal.rs b/crates/kernel/src/heal.rs
index fcd17878..b86c5858 100644
--- a/crates/kernel/src/heal.rs
+++ b/crates/kernel/src/heal.rs
@@ -404,6 +404,12 @@ pub fn heal(solid: Solid, size: f64) -> Solid {
 
 /// [`heal`], keeping faces apart along lines they were split along on purpose.
 pub(crate) fn heal_keep(solid: Solid, size: f64, keep: &[Vec<Vec3>]) -> Solid {
+    // Edges a boolean made are intersection curves, which panic where they no longer
+    // evaluate; the solid then stays as it is.
+    crate::guard("heal", || Ok(heal_shells(&solid, size, keep))).ok().flatten().unwrap_or(solid)
+}
+
+fn heal_shells(solid: &Solid, size: f64, keep: &[Vec<Vec3>]) -> Option<Solid> {
     let tol = (size * 1e-7).max(1e-9);
     let mut shells = Vec::new();
     let mut changed = false;
@@ -428,9 +434,9 @@ pub(crate) fn heal_keep(solid: Solid, size: f64, keep: &[Vec<Vec3>]) -> Solid {
         shells.push(cur);
     }
     if !changed {
-        return solid;
+        return None;
     }
-    Solid::try_new(shells).unwrap_or(solid)
+    Solid::try_new(shells).ok()
 }
 
 #[cfg(test)]
diff --git a/crates/kernel/src/ops.rs b/crates/kernel/src/ops.rs
index b812cbb7..1b9f9afd 100644
--- a/crates/kernel/src/ops.rs
+++ b/crates/kernel/src/ops.rs
@@ -296,7 +296,7 @@ fn boolean_whole(a: &Body, b: &Body, op: BoolOp) -> Result<Option<Body>> {
                     empty_votes += 1;
                     last = "empty result".into();
                 }
-                Ok(s) => match Body::new(crate::heal::heal_keep(s, size, &keep)) {
+                Ok(s) => match guard("boolean result", || Body::new(crate::heal::heal_keep(s, size, &keep))) {
                     Ok(body) => {
                         let (ok, v) = check(&body);
                         if ok {
diff --git a/examples/regressions/shallow_loft_cut_from_top_face.json b/examples/regressions/shallow_loft_cut_from_top_face.json
new file mode 100644
index 00000000..a898231b
--- /dev/null
+++ b/examples/regressions/shallow_loft_cut_from_top_face.json
@@ -0,0 +1,16 @@
+{
+ "description": "A shallow, wide loft cut starting in a body's top face: slab 900 x 480 x 160, loft cut from a 556.68 x 99 rectangle on the top face down 4 mm to an 80 x 80 square (sides about 0.9 degrees from horizontal). Healing an intermediate boolean result panicked outside the boolean's guard and stopped every later attempt. Result: the slab less the loft, 69 003 015.31 mm³.",
+ "commands": [
+  {"command": "sketch.create", "params": {"plane": "XY", "name": "Base"}},
+  {"command": "sketch.rectangle.two_point", "params": {"p0": [0, 0], "p1": [900, 480]}},
+  {"command": "sketch.finish", "params": {}},
+  {"command": "solid.extrude", "params": {"distance": 160, "name": "Slab"}},
+  {"command": "sketch.create", "params": {"plane": "XY", "offset": 160, "name": "LoftTop"}},
+  {"command": "sketch.rectangle.two_point", "params": {"p0": [171.66, 329.34], "p1": [728.34, 428.34]}},
+  {"command": "sketch.finish", "params": {}},
+  {"command": "sketch.create", "params": {"plane": "XY", "offset": 156, "name": "LoftBottom"}},
+  {"command": "sketch.rectangle.two_point", "params": {"p0": [410, 338.84], "p1": [490, 418.84]}},
+  {"command": "sketch.finish", "params": {}},
+  {"command": "solid.loft", "params": {"sections": [{"sketch": "LoftTop"}, {"sketch": "LoftBottom"}], "operation": "cut", "name": "LoftCut"}}
+ ]
+}