I'm like you. I get on famously with Claude Code with Opus 4.5 2025.11 update.
Give it a first pass from a spec. Since you know how it should be shaped you can give an initial steer, but focus on features first, and build with testability.
Then refactor, with examples in prompts, until it lines up. You already have the tests, the AI can ensure it doesn't break anything.
Beat it up more and you're done.
> focus on features first, and build with testability.
This is just telling me to do this:
> To use it the way you are using it we would instead have to allow it to replace the part that happens (or can happen) away from the keyboard: the mental processing of the code.
I don't want to do that.