What are you talking about?? Bun in Rust is a port, almost exactly the same code base on a different syntax. The architecture did not change at all. Amazing how people comment without even knowing what they are talking about.
Zig and Rust are significantly different languages. If bun has a good architecture in zig (which I don't know if it does or not), that doesn't necessarily mean it had a good architecture for rust. A direct translation of zig code would probably result in pretty unusual rust code, and probably a lot more unsafe usage than if it had been originally written in rust.
Very amazing indeed. Here you are making bold assumptions about a huge pile of code not a single human being has ever read in any meaningful amount.
Nobody reviewed resulting code. Maybe all tests are empty and this is why they pass. Maybe tests were modified to pass because this is the only thing LLM could do to make them pass. Maybe it hallucinated something in the process. We have no idea.