I have to leave my 9yo neutered male cat with my parents over the summer while I pursue an internship across the U.S. I absolutely cannot bring him for the summer, but I will be able to once I am in a more stable living situation post-internship (I'm 23). I pay for all of his vet care, food, toys, etc. All I'm asking is that my folks fulfill his basic needs while I'm gone, which they have agreed to.
The issue is, he keeps escaping outside through their lack of attention/care. He used to be an outside cat years ago, and now bolts for the door any chance he gets. He's leash trained and we go out for 30mins every morning, but it still won't satisfy him. I obviously don't want him outside, as he will decimate local wildlife and get injured/killed etc. So, my question is, would it be cruel to keep him confined to my bedroom for the summer? It's pretty large, about 15'×20' feet with lots of vertical space for him to explore. I also bought a 5'×5' catio that I am going to attach to one of the bedroom windows this week, so he will still have some (contained) outside access.
TLDR: Would it be cruel to confine a 9yo cat to a large bedroom with an attached catio for the summer in an attempt to prevent outside escapes?