I'm not super surprised that these examples worked well. They are complex and a ton of work, but the problems are relatively well defined with tons of documentation online. Sounds ideal for an LLM no?

Yes, that's a point I've been trying to emphasize: if a problem is well specified a coding agent can crunch for hours on it to get to a solution.

Even better if there's an existing conformance suite to point at - like html5lib-tests or the WenAssembly spec tests.