Good day. I have a solution to your problem. You need to add an empty package.json file to the project in the following format:

{ "name": "", "description": "", "version": "0.1.0", "dependencies": {}, "devDependencies": {} }

After this, Vaadin will generate all dependencies and will not delete the frontend part.

Long explanation: Vaadin assumes that if there is no customization in the application, it dynamically generates the frontend, builds it into an artifact, and deletes it. The presence of even an empty package.json is considered a sign of customization.