Fix perpendicular fillets after connected rounds (#1581)

Thanks @cfaulkingham.

crates/engine/src/cmd/features.rs

@@ -1888,3 +1888,6 @@ mod thin_extrude_tests;
 #[cfg(test)]
 #[path = "extrude_convention_tests.rs"]
 mod extrude_convention_tests;
+#[cfg(test)]
+#[path = "fillet_connected_rounds_tests.rs"]
+mod fillet_connected_rounds_tests;

crates/engine/src/cmd/fillet_connected_rounds_tests.rs

@@ -0,0 +1,64 @@
+use serde_json::{Value, json};
+
+use crate::Session;
+
+fn run(s: &mut Session, command: &str, params: Value) -> Value {
+    s.execute(command, &params).unwrap_or_else(|e| panic!("{command}: {e}"))
+}
+
+fn bottom_rounds() -> Session {
+    let mut s = Session::default();
+    run(&mut s, "parameters.change", json!({"name":"corner_radius", "expression":"2 mm"}));
+    run(&mut s, "sketch.create", json!({"plane":"XY", "name":"Rectangle"}));
+    run(&mut s, "sketch.rectangle.two_point", json!({"p0":[0,0], "p1":[25,25]}));
+    run(&mut s, "sketch.finish", json!({}));
+    run(&mut s, "solid.extrude", json!({"distance":"10 mm", "body_name":"Block"}));
+    run(&mut s, "solid.fillet", json!({"edges":[[12.5,0,0],[25,12.5,0],[12.5,25,0],[0,12.5,0]], "radius":"2 mm"}));
+    s
+}
+
+fn volume(s: &mut Session) -> f64 {
+    let value = run(s, "inspect.measure", json!({}));
+    assert_eq!(value["body_count"], 1);
+    let state = s.model.state();
+    let body = &state.body("Block").unwrap().body;
+    assert!(body.validity().is_empty(), "{:?}", body.validity());
+    value["total"]["volume_mm3"].as_f64().unwrap()
+}
+
+#[test]
+fn issue1557_fillet_recomputes_and_survives_undo_and_reload() {
+    for edges in [json!([[25, 0, 6]]), json!([[25, 0, 6], [24.287266336668306, 0.7127336633316916, 0.48266373325510686]])] {
+        let mut s = bottom_rounds();
+        let before = volume(&mut s);
+        let out = run(&mut s, "solid.fillet", json!({"edges":edges, "radius":"corner_radius"}));
+        let id = out["feature"].as_u64().unwrap();
+        let after = volume(&mut s);
+        assert!(after < before - 1.0);
+        assert_eq!(s.doc.features.len(), 4);
+        run(&mut s, "edit.undo", json!({}));
+        assert!((volume(&mut s) - before).abs() < 1e-6);
+        run(&mut s, "edit.redo", json!({}));
+        assert!((volume(&mut s) - after).abs() < 1e-6);
+        run(&mut s, "parameters.change", json!({"name":"corner_radius", "expression":"1 mm"}));
+        let smaller = volume(&mut s);
+        assert!(smaller > after && smaller < before);
+        assert!(run(&mut s, "timeline.inspect", json!({"feature":id}))["error"].is_null());
+        let bytes = crate::io::write_design_container(&s.doc).unwrap();
+        let mut reopened = Session::new(crate::io::read_design(&bytes).unwrap());
+        assert!((volume(&mut reopened) - smaller).abs() < 1e-6);
+        assert_eq!(reopened.doc.features.len(), 4);
+    }
+}
+
+#[test]
+fn issue1557_failed_radius_keeps_the_existing_rounds() {
+    let mut s = bottom_rounds();
+    let before = s.doc.to_json();
+    let v = volume(&mut s);
+    let undo = s.undo.len();
+    assert!(s.execute("solid.fillet", &json!({"edges":[[25,0,6]], "radius":"1000 mm"})).is_err());
+    assert_eq!(s.doc.to_json(), before);
+    assert_eq!(s.undo.len(), undo);
+    assert!((volume(&mut s) - v).abs() < 1e-6);
+}