Coming at this as someone who has stepped away from coding more than once for multiple-year long stints due to various career choices - I think the concern of "skill rot" is overblown.

I stopped writing C++ professionally in the early 2010's. I came back to it in the early 2020's and it was extremely easy to pick up. Less like riding a bike, more like driving a car. The car got better over the last 10 years, but it still takes a bit of time to fully meld with the machine. The skills didn't rot, they just fell behind, and catching up wasn't a big deal.

I think the only "skill rot" people are facing today when coding by hand vs by agent is that you know you're doing something the hard way when you know there is another path of least resistance available - and that creates internal resistance to doing it the hard way. It's a mental block, not skill rot.

The one area I do find myself questioning is that my low level tech skills aren't growing - I'm building bigger projects that do more stuff across more areas, and as a result I'm touching lots of new technologies from a birds eye view and directing the agents to do stuff with them. I'm not personally gaining that experience of using those technologies, whereas if I were doing things the old way I would be deep in the weeds and have to know them in depth. But if I were doing things the old way I probably wouldn't be building such ambitious projects as a solo dev either.

IMO it's more like digging out the foundation with shovels vs using an excavator. You don't lose the shoveling skill by using the excavator, but you sure feel like a chump using a shovel when there's an excavator parked and ready next to the job site.

Maybe it only applies to people at the top of their game; pro atheletes and musicians need regular practice, the rest of us can use most of our skills without that.