frontend-app-api: add session boundary app initialization

Instantiate the app shell up to app/root.children during sign-in, then rebuild the full tree after sign-in without cloning the app tree.

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

plugins/app/src/extensions/AppRoot.tsx

@@ -73,6 +73,7 @@ export const AppRoot = createExtension({
     }),
     children: createExtensionInput([coreExtensionData.reactElement], {
       singleton: true,
+      optional: true,
     }),
     elements: createExtensionInput([coreExtensionData.reactElement]),
     wrappers: createExtensionInput(
@@ -105,9 +106,7 @@ export const AppRoot = createExtension({
       });
     }
 
-    let content: ReactNode = inputs.children.get(
-      coreExtensionData.reactElement,
-    );
+    let content = inputs.children?.get(coreExtensionData.reactElement);
 
     for (const wrapper of inputs.wrappers) {
       const Component = wrapper.get(AppRootWrapperBlueprint.dataRefs.component);