add defensive handling of vscode api proposal usage

Author: jankuca

src/notebooks/controllers/vscodeNotebookController.ts

@@ -173,10 +173,14 @@ export class VSCodeNotebookController implements Disposable, IVSCodeNotebookCont
             displayDataProvider
         );
 
-        try {
-            controller.controller.variableProvider = jupyterVairablesProvider;
-        } catch (ex) {
-            logger.warn('Failed to attach variable provider', ex);
+        // Only attach variable provider if the API is available
+        // Some VSCode forks (like Cursor) don't support the notebookVariableProvider API proposal yet
+        if ('variableProvider' in controller.controller) {
+            try {
+                controller.controller.variableProvider = jupyterVairablesProvider;
+            } catch (ex) {
+                logger.warn('Failed to attach variable provider', ex);
+            }
         }
 
         return controller;