This seems really impressive. I am too lazy to replicate this, but I do wonder how important the test suite is for a a port that likely uses straight forward, dependency free python code https://github.com/EmilStenstrom/justhtml/tree/main/src/just...

It is enormously useful for the author to know that the code works, but my intuition is if you asked an agent to port files slowly, forming its own plan, making commits every feature, it would still get reasonably close, if not there.

Basically, I am guessing that this impressive output could have been achieved based on how good models are these days with large amounts of input tokens, without running the code against tests.