If I read it and memorize it, my brain has made a copy.
Whether that copy was fair use is the key question.
I bought a license to listen and use.
But as you point out in the router case above, it's transient.
Anyway, I've always been a bit prickly about IP stuff ever since a troll lawyer threatened me over a TI-BASIC game when I was like 14. I'm also sure I'm completely wrong-headed about this whole thing and overly anthropomorphizing the LLM.