Join keeps its tool exact where the tool ends in the part's faces (#1244)

crates/engine/src/tests/boolean_diagnostics.rs

@@ -50,3 +50,35 @@ fn boolean_retry_warning_and_details_survive_cache_undo_and_reopen() {
     assert!(last.warning.is_none());
     assert!(last.boolean_diagnostics.events.is_empty());
 }
+
+/// A barrel joined under a plate's back edge, its ends flush with the sides of the leaf it hangs
+/// from (#827 without its fillets): the join is exact, so the command's reply carries no Boolean
+/// retry, and the barrel's ends stay in the leaf's sides (it is not nudged to make the join go).
+#[test]
+fn a_barrel_joined_between_the_sides_of_a_leaf_needs_no_retry() {
+    let mut session = Session::default();
+    run(&mut session, "solid.box", json!({"length": 40, "width": 20, "height": 6, "corner": [0, 0, 5], "body_name": "Plate"}));
+    run(&mut session, "solid.box", json!({"length": 14, "width": 10, "height": 6, "corner": [10, 10, 0], "operation": "join", "targets": ["Plate"]}));
+    let reply = run(
+        &mut session,
+        "solid.cylinder",
+        json!({"radius": 5, "height": 14, "axis": "X", "base": [10, 20, 0], "operation": "join", "targets": ["Plate"]}),
+    );
+    assert!(reply["warning"].is_null(), "{reply}");
+    let result = session.model.result(reply["feature"].as_u64().unwrap()).unwrap();
+    assert!(result.boolean_diagnostics.events.is_empty(), "{:?}", result.boolean_diagnostics);
+    let state = session.model.state();
+    let plate = &state.body("Plate").unwrap().body;
+    assert_eq!(plate.shell_count(), 1);
+    assert!(plate.validity().is_empty(), "{:?}", plate.validity());
+    // Every edge ends on a level along x of the plate, the leaf or the barrel.
+    for edge in plate.edges(1e-3).unwrap() {
+        for p in [edge.points.first(), edge.points.last()].into_iter().flatten() {
+            assert!([0., 10., 24., 40.].iter().any(|x| (p.x - x).abs() < 1e-9), "an edge ends at {p:?}");
+        }
+    }
+    // A quarter of the barrel lies in the leaf.
+    let expected = 5500. + 0.75 * PI * 25. * 14.;
+    let actual = plate.tessellate(1e-4).unwrap().measure().volume;
+    assert!(rel(actual, expected) < 1e-5, "{actual} vs {expected}");
+}