fix: refuse Boolean retries that change the part away from the tool (#616) (#644)

Joining ribs flush with a lid's window left a zero-thickness slit far from the rib (the planar fallback glued back only one of the faces its pieces shared) and displaced the tool on the other joins. Gluing now joins every shared face pair, coincident-face separation checks there is material behind a pushed face for every join, and any join or cut that needed a retry must be closed, keep volume monotonic and leave the part unchanged outside the tool's box, or it is refused with an error. Feature command replies carry the feature's warning.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/boolean_regression_tests.rs

@@ -118,3 +118,38 @@ fn ring_cut_below_a_recess_keeps_the_part_in_one_body() {
     let got = volume(&s, "Frame");
     assert!((got - want).abs() < 1e-9 * want, "{got} vs {want}");
 }
+
+/// Four ribs joined on a rounded lid, standing on the plate over the skirt and flush with the
+/// window's sides: each adds exactly its own material and nothing changes away from it. The
+/// joins displaced the tool and one left a slit through the far side of the skirt and plate
+/// (#616), which no volume shows: the area does. The reply of each join carries its warning, as
+/// the timeline does (an agent placing parts over MCP saw none).
+#[test]
+fn ribs_flush_with_a_window_change_nothing_away_from_them() {
+    let script: Value = serde_json::from_str(include_str!("../../../examples/regressions/lid_ribs_flush_with_window.json")).unwrap();
+    let steps = script.get("commands").and_then(Value::as_array).unwrap();
+    let (lid, ribs) = steps.split_at(steps.len() - 4);
+    let mut s = Session::default();
+    s.run_script(&Value::Array(lid.to_vec())).unwrap();
+    let measure = |s: &Session| s.model.state().body("Lid").map(|b| solidcraft_kernel::measure(&b.body).unwrap()).unwrap();
+    let (v0, a0) = (measure(&s).volume, measure(&s).area);
+    assert!((v0 - 6703.5222).abs() < 1e-3, "{v0}");
+    for (i, rib) in ribs.iter().enumerate() {
+        let reply = s.execute(rib["command"].as_str().unwrap(), &rib["params"]).unwrap();
+        let id = reply["feature"].as_u64().unwrap();
+        let result = s.model.result(id).unwrap();
+        assert_eq!(reply["warning"], json!(result.warning), "the reply says what the timeline says");
+        assert!(!result.warning.as_deref().unwrap_or_default().contains("tool displacement"), "{:?}", result.warning);
+        let m = measure(&s);
+        let n = (i + 1) as f64;
+        // 1.6 x 6 x 11.7 less the 1.35 x 6 x 3 inside the skirt.
+        assert!((m.volume - (v0 + n * 88.02)).abs() < 1e-6, "rib {}: {}", i + 1, m.volume - v0);
+        // Top 9.6, outer side 6 x 8.7 above the skirt, inner side 6 x 11.7 (flush with the
+        // window's side), ends 2 x (1.6 x 11.7 - 1.35 x 3); the skirt top 8.1, its inner side
+        // 18 and 1.5 of the plate go under the rib.
+        let area = 9.6 + 52.2 + 70.2 + 29.34 - 8.1 - 18.0 - 1.5;
+        assert!((m.area - (a0 + n * area)).abs() < 1e-6, "rib {}: area {} (no slit adds any)", i + 1, m.area - a0);
+    }
+    let bounds = s.model.state().body("Lid").unwrap().body.tessellate(0.01).unwrap().bounds();
+    assert!((bounds.max.z - 14.1).abs() < 1e-9, "{}", bounds.max.z);
+}