I will probably end up regretting this since I assume the "wait to be given an input from some other process before continuing execution" paradigm is going to come up again, but this part 2 goroutine+channel solution felt good (taking advantage of Go features) and made me happy, so I rolled with it.
I'm reasonably happy with this. I started with a bi-directional linked list, but realized that a flat list of all nodes came in handy for one use case while the linked list came in handy for another, so I settled on that.
This required an overhaul of the intcode machine to actually be its own type that could operate on its own memory and stuff. So I had to touch day 2 to make it adhere to the new API.
Feeling good about this foundation now. Until I get gobsmacked at some point later, which I expect to happen.
