A fillet of a vanished edge says the name is gone (#775) (#1066)

A fillet or chamfer whose picked edge no longer exists now says the edge's name is gone instead of failing on an unrelated edge (#775).

crates/engine/src/naming_history_tests.rs

@@ -271,3 +271,31 @@ fn a_sketch_on_a_certified_face_survives_a_fillet_and_a_cut_upstream_of_it() {
     }
     assert!((top(&s) - 20.0).abs() < 1e-6, "{}", top(&s));
 }
+
+/// A fillet of a shell's inner corners names those edges. Thinning the wall past the outer
+/// round removes them. The fillet must say the names are gone, not blend the seam nearest
+/// the old pick, which now sits on the axis of the inner round (#775).
+#[test]
+fn a_shell_fillet_does_not_follow_a_gone_edge_onto_a_smooth_seam() {
+    let mut s = Session::default();
+    run(&mut s, "sketch.create", json!({"plane": "XY"}));
+    run(&mut s, "sketch.rectangle.two_point", json!({"p0": [-27.5, -40], "p1": [27.5, 40]}));
+    run(&mut s, "sketch.finish", json!({}));
+    run(&mut s, "solid.extrude", json!({"distance": 25, "name": "Extrude1"}));
+    run(
+        &mut s,
+        "solid.fillet",
+        json!({"radius": 5, "name": "Fillet1", "edges": [[-27.5, -40, 12.5], [27.5, -40, 12.5], [27.5, 40, 12.5], [-27.5, 40, 12.5]]}),
+    );
+    run(&mut s, "solid.shell", json!({"faces": [[0, 0, 25]], "thickness": 5, "direction": "inside", "name": "Shell1"}));
+    run(
+        &mut s,
+        "solid.fillet",
+        json!({"radius": 5, "name": "Fillet2", "edges": [[-22.5, 35, 15], [22.5, 35, 15], [22.5, -35, 15], [-22.5, -35, 15]]}),
+    );
+    assert_eq!(error(&s, "Fillet2"), None);
+    let edited = s.execute("timeline.edit", &json!({"feature": "Shell1", "set": {"thickness": "2"}}));
+    let message = error(&s, "Fillet2").or_else(|| edited.err().map(|e| e.to_string())).unwrap_or_default();
+    assert!(message.contains("no longer exists"), "{message}");
+    assert!(!message.contains("smooth edge"), "{message}");
+}