Preserve app loading fallback in createDevApp.

Only suspend the lazy BUI CSS import so the app root keeps its built-in loading UI, and lock that behavior down in the mocked render test.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

packages/frontend-dev-utils/src/createDevApp.test.tsx

@@ -134,6 +134,11 @@ describe('createDevApp', () => {
       });
       expect(createRoot).toHaveBeenCalledWith(root);
     });
+
+    const renderedNode = render.mock.calls[0][0] as any;
+    expect(renderedNode.props.children).toHaveLength(2);
+    expect(renderedNode.props.children[0].props.fallback).toBeNull();
+    expect(renderedNode.props.children[1].props.children).toBe('Test App Root');
   });
 
   it('should throw a clear error when the root element is missing', () => {

packages/frontend-dev-utils/src/createDevApp.tsx

@@ -108,10 +108,12 @@ export function createDevApp(options: CreateDevAppOptions): void {
 
   ReactDOMPromise.then(ReactDOM => {
     const rootNode = (
-      <Suspense fallback={null}>
-        <BuiCss />
+      <>
+        <Suspense fallback={null}>
+          <BuiCss />
+        </Suspense>
         {AppRoot}
-      </Suspense>
+      </>
     );
 
     if ('createRoot' in ReactDOM) {