As stated near the end of the article, this isn’t something you’d do much as an app developer. The article describes how to pull but the predominant model for building apps is to have the data pushed to you. So in practice you’d use at:// URIs as unique identifiers for the data you’re receiving and indexing on your backend, not something you actually need to resolve. You wouldn't need to resolve them because you'd be receiving the JSON itself via the websocket.
To add, it's largely required for an app to listen to the event stream because a user may write a record you care about directly (not through your app), and you likely want to know about that as "real-time" as possible. Crawling will never get you close to that
