diff --git a/crates/engine/src/shapebuilder.rs b/crates/engine/src/shapebuilder.rs
index 09a6758a..99d59b45 100644
--- a/crates/engine/src/shapebuilder.rs
+++ b/crates/engine/src/shapebuilder.rs
@@ -322,7 +322,7 @@ fn apply(s: &mut Session, cmd: &str, p: &Value, merge: bool) -> Result<Value> {
     let whole_shape =
         touched.len() == 1 && a.regions.iter().enumerate().all(|(i, r)| pick.contains(&i) || !r.sources.iter().any(|x| touched.contains(x)));
     if merge && whole_shape {
-        return Ok(json!({"id": null, "changed": [], "removed": [], "regions": pick}));
+        return Ok(json!({"id": null, "changed": [], "removed": [], "outlines": [], "regions": pick}));
     }
     let doc = s.doc_mut()?;
     let created = if merge {
diff --git a/crates/engine/tests/shape_builder_response.rs b/crates/engine/tests/shape_builder_response.rs
new file mode 100644
index 00000000..e1426823
--- /dev/null
+++ b/crates/engine/tests/shape_builder_response.rs
@@ -0,0 +1,36 @@
+#![allow(clippy::unwrap_used, clippy::expect_used, clippy::panic)]
+use figcraft_engine::Session;
+use serde_json::{Value, json};
+
+fn rectangle(s: &mut Session, x: f64) -> Value {
+    s.execute("shape.rectangle", &json!({"x": x, "y": 0, "width": 100, "height": 100})).unwrap()["id"].clone()
+}
+
+#[test]
+fn merge_response_includes_outlines_for_no_op() {
+    let mut s = Session::new();
+    let id = rectangle(&mut s, 0.0);
+    let regions = s.execute("shapeBuilder.regions", &json!({"ids": [id]})).unwrap();
+    assert_eq!(regions["regions"].as_array().unwrap().len(), 1);
+    let before = serde_json::to_value(s.doc().unwrap()).unwrap();
+    let result = s.execute("shapeBuilder.merge", &json!({"ids": [id], "regions": [0]})).unwrap();
+    assert_eq!(serde_json::to_value(s.doc().unwrap()).unwrap(), before);
+    assert_eq!(result["id"], Value::Null);
+    assert_eq!(result["changed"], json!([]));
+    assert_eq!(result["removed"], json!([]));
+    assert_eq!(result["regions"], json!([0]));
+    assert_eq!(result.get("outlines"), Some(&json!([])));
+}
+
+#[test]
+fn merge_response_control_includes_outlines() {
+    let mut s = Session::new();
+    let a = rectangle(&mut s, 0.0);
+    let b = rectangle(&mut s, 50.0);
+    let regions = s.execute("shapeBuilder.regions", &json!({"ids": [a, b]})).unwrap();
+    assert_eq!(regions["regions"].as_array().unwrap().len(), 3);
+    let result = s.execute("shapeBuilder.merge", &json!({"ids": [a, b], "regions": [1]})).unwrap();
+    assert!(result["id"].is_u64());
+    assert_eq!(result.get("outlines"), Some(&json!([])));
+    assert_eq!(result.as_object().unwrap().len(), 5);
+}