How would you characterize code is easy for AI to write code against. - and wouldn't that also be true for humans?

AI is greatly aided by clear usage examples and trigger calls, such as "Use when [xyz]" types of standard comments.

All relevant code fits in context. Functional APIs. Standard data structures. Design documents for everything.

I'm doing this in a Clojure context, so that helps—the core language/libraries are unusually stable and widely used and so feature-complete there's basically no hallucinations.