You don’t need APIs if your app includes a web browser, though; you just need the patience to hook into the browser’s APIs, rather than the page’s, in order to backup content when viewed. User-operated Selenium is legitimately the biggest threat model to content islands. It’s too bad a third-party had to invent Grayjay as a standalone, rather than one of the browsers figuring this out and shipping it as subscription-payment functionality :/

(It has to be subscription payment to deal in a scaleable and timely manner with sites changing their page schemas anticompetitively.)