add vscode.notebooks.notebookDocuments-api, https://github.com/microsoft/vscode/issues/93265

src/vs/vscode.proposed.d.ts

@@ -1636,6 +1636,12 @@ declare module 'vscode' {
 
 		export const onDidOpenNotebookDocument: Event<NotebookDocument>;
 		export const onDidCloseNotebookDocument: Event<NotebookDocument>;
+
+		/**
+		 * All currently known notebook documents.
+		 */
+		export const notebookDocuments: ReadonlyArray<NotebookDocument>;
+
 		export let visibleNotebookEditors: NotebookEditor[];
 		export const onDidChangeVisibleNotebookEditors: Event<NotebookEditor[]>;
 

src/vs/workbench/api/common/extHost.api.impl.ts

@@ -921,10 +921,16 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 				checkProposedApiEnabled(extension);
 				return extHostNotebook.onDidCloseNotebookDocument;
 			},
+			get notebookDocuments(): vscode.NotebookDocument[] {
+				checkProposedApiEnabled(extension);
+				return extHostNotebook.notebookDocuments;
+			},
 			get visibleNotebookEditors() {
+				checkProposedApiEnabled(extension);
 				return extHostNotebook.visibleNotebookEditors;
 			},
 			get onDidChangeVisibleNotebookEditors() {
+				checkProposedApiEnabled(extension);
 				return extHostNotebook.onDidChangeVisibleNotebookEditors;
 			},
 			registerNotebookContentProvider: (viewType: string, provider: vscode.NotebookContentProvider) => {

src/vs/workbench/api/common/extHostNotebook.ts

@@ -678,6 +678,10 @@ export class ExtHostNotebookController implements ExtHostNotebookShape, ExtHostN
 		return this._activeNotebookEditor;
 	}
 
+	get notebookDocuments() {
+		return [...this._documents.values()];
+	}
+
 	private _onDidOpenNotebookDocument = new Emitter<vscode.NotebookDocument>();
 	onDidOpenNotebookDocument: Event<vscode.NotebookDocument> = this._onDidOpenNotebookDocument.event;
 	private _onDidCloseNotebookDocument = new Emitter<vscode.NotebookDocument>();

src/vs/workbench/test/browser/api/extHostNotebookConcatDocument.test.ts

@@ -73,7 +73,7 @@ suite('NotebookConcatDocument', function () {
 		});
 		await extHostNotebooks.$acceptDocumentAndEditorsDelta({ newActiveEditor: '_notebook_editor_0' });
 
-		notebook = extHostNotebooks.activeNotebookDocument!;
+		notebook = extHostNotebooks.notebookDocuments[0]!;
 
 		disposables.add(reg);
 		disposables.add(notebook);