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/engine/src/tests/robustness.rs

@@ -79,6 +79,37 @@ fn shell_thicker_than_a_step_says_so() {
     assert!(e.to_string().contains("not supported yet"), "{e}");
 }
 
+/// Panics inside the kernel are caught natively, but abort the web build (wasm can't unwind).
+/// Building the samples must not panic at all (the Plastic Enclosure's bosses used to, 8 times).
+#[test]
+fn samples_build_without_panics() {
+    use std::sync::Arc;
+    use std::sync::atomic::{AtomicUsize, Ordering};
+    let me = std::thread::current().id();
+    let count = Arc::new(AtomicUsize::new(0));
+    let c2 = count.clone();
+    let prev = std::panic::take_hook();
+    std::panic::set_hook(Box::new(move |info| {
+        if std::thread::current().id() == me {
+            c2.fetch_add(1, Ordering::SeqCst);
+        }
+        let _ = info;
+    }));
+    let mut failed = Vec::new();
+    for sample in crate::sample::samples() {
+        let mut s = Session::default();
+        for c in (sample.script)()["commands"].as_array().into_iter().flatten() {
+            let _ = s.execute(c["command"].as_str().unwrap_or(""), &c["params"]);
+        }
+        let n = count.swap(0, Ordering::SeqCst);
+        if n > 0 {
+            failed.push(format!("{}: {n} panic(s)", sample.name));
+        }
+    }
+    std::panic::set_hook(prev);
+    assert!(failed.is_empty(), "{failed:?}");
+}
+
 /// Seeds that run clean: no failure, no invalid body, no volume going the wrong way.
 #[test]
 fn fixed_seeds_run_clean() {