diff --git a/app/index.js b/app/index.js
index cafb6ed7d2..61a9661d31 100644
--- a/app/index.js
+++ b/app/index.js
@@ -83,6 +83,7 @@ async function main() {
     require('@jupyterlab/apputils-extension').default.filter(({ id }) =>
       [
         '@jupyterlab/apputils-extension:palette',
+        '@jupyter/apputils-extension:sanitizer',
         '@jupyterlab/apputils-extension:settings',
         '@jupyterlab/apputils-extension:state',
         '@jupyterlab/apputils-extension:themes',
@@ -135,6 +136,7 @@ async function main() {
         '@jupyterlab/notebook-extension:code-console',
         '@jupyterlab/notebook-extension:export',
         '@jupyterlab/notebook-extension:factory',
+        '@jupyterlab/notebook-extension:toc',
         '@jupyterlab/notebook-extension:tracker',
         '@jupyterlab/notebook-extension:widget-factory'
       ].includes(id)
diff --git a/packages/application-extension/src/index.ts b/packages/application-extension/src/index.ts
index f4c3d904a0..5e65911d31 100644
--- a/packages/application-extension/src/index.ts
+++ b/packages/application-extension/src/index.ts
@@ -185,7 +185,7 @@ const opener: JupyterFrontEndPlugin<void> = {
 
     const command = 'router:tree';
     commands.addCommand(command, {
-      execute: (args: any) => {
+      execute: async (args: any) => {
         const parsed = args as IRouter.ILocation;
         const matches = parsed.path.match(TREE_PATTERN) ?? [];
         const [, , path] = matches;
@@ -195,12 +195,11 @@ const opener: JupyterFrontEndPlugin<void> = {
 
         const file = decodeURIComponent(path);
         const ext = PathExt.extname(file);
-        app.restored.then(async () => {
+        await new Promise(async () => {
           // TODO: get factory from file type instead?
           if (ext === '.ipynb') {
             // TODO: fix upstream?
             await settingRegistry?.load('@jupyterlab/notebook-extension:panel');
-            await Promise.resolve();
             docManager.open(file, NOTEBOOK_FACTORY, undefined, {
               ref: '_noref'
             });
diff --git a/packages/application/src/app.ts b/packages/application/src/app.ts
index 4c5ff461f8..e3392e2970 100644
--- a/packages/application/src/app.ts
+++ b/packages/application/src/app.ts
@@ -37,6 +37,11 @@ export class NotebookApp extends JupyterFrontEnd<INotebookShell> {
         this.registerPlugin(plugin);
       }
     }
+
+    this.restored = this.shell.restored
+      .then(() => undefined)
+      .catch(() => undefined);
+
     this.restored.then(() => this._formatter.invoke());
   }
 
@@ -55,6 +60,12 @@ export class NotebookApp extends JupyterFrontEnd<INotebookShell> {
    */
   readonly status = new LabStatus(this);
 
+  /**
+   * Promise that resolves when state is first restored, returning layout
+   * description.
+   */
+  readonly restored: Promise<void>;
+
   /**
    * The version of the application.
    */
diff --git a/packages/application/src/shell.ts b/packages/application/src/shell.ts
index 7cf764acf1..d336525df3 100644
--- a/packages/application/src/shell.ts
+++ b/packages/application/src/shell.ts
@@ -6,7 +6,7 @@ import { PageConfig } from '@jupyterlab/coreutils';
 import { DocumentRegistry } from '@jupyterlab/docregistry';
 
 import { ArrayExt, find, IIterator, iter } from '@lumino/algorithm';
-import { Token } from '@lumino/coreutils';
+import { PromiseDelegate, Token } from '@lumino/coreutils';
 import { Message, MessageLoop, IMessageHandler } from '@lumino/messaging';
 import { Debouncer } from '@lumino/polling';
 import { ISignal, Signal } from '@lumino/signaling';
@@ -75,12 +75,10 @@ export class NotebookShell extends Widget implements JupyterFrontEnd.IShell {
     } else {
       this.layout = this.initLayoutWithoutSidePanels();
     }
-
   }
 
   initLayoutWithoutSidePanels(): Layout {
     const rootLayout = new BoxLayout();
-
     BoxLayout.setStretch(this._main, 1);
 
     this._spacer = new Widget();
@@ -211,6 +209,13 @@ export class NotebookShell extends Widget implements JupyterFrontEnd.IShell {
     return !(this._rightHandler.isVisible && this.rightPanel.isVisible);
   }
 
+  /**
+   * Promise that resolves when main widget is loaded
+   */
+  get restored(): Promise<void> {
+    return this._mainWidgetLoaded.promise;
+  }
+
   /**
    * Activate a widget in its area.
    */
@@ -259,6 +264,7 @@ export class NotebookShell extends Widget implements JupyterFrontEnd.IShell {
         this._main.addWidget(widget);
         this._main.update();
         this._currentChanged.emit(void 0);
+        this._mainWidgetLoaded.resolve();
         break;
       case 'left':
         if (this.sidePanelsVisible()) {
@@ -410,6 +416,7 @@ export class NotebookShell extends Widget implements JupyterFrontEnd.IShell {
   private _spacer: Widget;
   private _main: Panel;
   private _currentChanged = new Signal<this, void>(this);
+  private _mainWidgetLoaded = new PromiseDelegate<void>();
 }
 
 /**