Are you implying a direct bug for bug port is more expensive than converting to an intermediate representation and then converting via generators? Depending on the "fidelity" of the representation I'd figure the costs are about the same.
My understanding is, direct port is more expensive besides toy projects of course, looking at Bun and also listening to people who've done a few language conversions, they extract something first.
If not an intermediate representation, my first question would be: how to split the work. You cannot just prompt full rewrite of 60K LoC, you cannot do it module by module — modules do translate 1:1, like in my case golang packages did not matched Rust crates. Bun did file by file.
With hierarchical state machines in the middle, I did it almost in one shot.