Here's one to get reports from visible users.

The app sends to "usersToWatch" every visible reference to a user: think of all profile pictures, names, inside note quotes, and even raw @pubs in the content. At every point in time, there are 5(feed) - 100 (notifications) Nostr users being seen by the user. As the user scrolls, users of interest are added and removed from the list automatically. Meanwhile, this class sends a filter to get Reports from all relays for each user, but only reports since the last time it got those reports for each user.

https://github.com/vitorpamplona/amethyst/blob/b0953310c2d2eb82131e204d35f6d81b7832c0c3/app/src/main/java/com/vitorpamplona/amethyst/service/NostrSingleUserDataSource.kt#L29