cloneInstance fix: preserve children

integration/rendering.test.tsx

@@ -253,13 +253,18 @@ test("button onClick", async () => {
 test("button click with state", async () => {
   function Counter() {
     const [count, setCount] = useState(0)
-    return <Button onClick={() => setCount(count + 1)}>{count}</Button>
+    return (
+      <>
+        the count is {count}
+        <Button onClick={() => setCount(count + 1)}>increment</Button>
+      </>
+    )
   }
 
   async function assertCount(count: number) {
     await assertMessages([
       {
-        content: "_ _",
+        content: `the count is ${count}`,
         components: [
           {
             type: "ACTION_ROW",
@@ -267,7 +272,7 @@ test("button click with state", async () => {
               {
                 type: "BUTTON",
                 style: "SECONDARY",
-                label: String(count),
+                label: "increment",
                 disabled: false,
               },
             ],

src/reconciler.ts

@@ -89,7 +89,16 @@ export const reconciler = ReactReconciler<
     type: ElementTag,
     oldProps: Props,
     newProps: Props,
-  ) => createInstance(type, newProps),
+  ) => {
+    const newInstance = createInstance(type, newProps)
+
+    // instance children don't get carried over, so we need to copy them
+    if ("children" in instance && "children" in newInstance) {
+      newInstance.children = instance.children
+    }
+
+    return newInstance
+  },
 
   // returning a non-null value tells react to re-render the whole thing
   // on any prop change