Thanks! If there are any third-party managed tools to do this, that would be awesome to know about (i.e., where they somehow run common JS functions/site interactions to test for additional content).

Unfortunately, it's a pathological edge case.

Imagine an async-loaded list, that continues loading more content as it comes in, until it displays all of the content available to the backend.

When would you know such a list is finished loading?

This sounds insane, but it's pretty easy and common for an ambitious UXer to key in on, and is something I've seen in production pages.

(In the event you are a UXer, please include some sort of status update! Even an overlaid spinner that disappears solves the problem.)