system
A chat on subreddit /r/PoliticalCompassMemes
human
The real answer? 
The feds aren't really on a lot of these online spaces to go undercover and make arrests. That's more for dark web and chatrooms and such.

The ones you see on places like Reddit or 4chan are there to essentially study people, they're trying to figure out online culture so that they can have things like profiles, run into "persons of interest", and figure out how to manipulate online social climates.

Feds actually aren't typically allowed to access that kind of bulk data they've collected without getting a warrant or some kind of authorization after they already suspect something. Otherwise, the data is basically being used to create a picture, profiles of different types of people in these spaces so that they have tactics at the ready to deal with "problem" areas of the internet.
gpt
Awesome. I kind of wish I were a CIA agent.

By the way, do you really call CIA agents feds? I thought feds were from the FBI, and the CIA works globally.