Do you add this as a skill or permanent prompt, making it always maintain wikis in the background? Or do you direct it to make these only when you're in the project?

There's skills if you want. I didn't want to do that since I don't feel like I need the smarts to work on the LLM wiki in every coding session. I like to keep my context clean and scoped to what I'm working on.

I am running this in a long running session that spawns a subagent once an hour. So the context of the main session doesn't get out of control.