alt Hacker Newsmy read is that with the right guidance, implementing the vast amount of the CSS spec for example, could be done easily with some AI assistance, the spec is incredibly well defined. just comparing the layouting and styling in blitz[0] (which does use agents), servo is lacking quite a bit, and the implementation of various features don't follow the spec exactly.
that being said, i entirely respect their decision of course, perhaps they will revisit at a later point in time!
(I'm the maintainer of Blitz)
My experience is that it varies greatly by feature.
Something like border styles, the agent was able to do pretty effectively. Although it still took a few hours iterating on it to get the performance characteristics and edge cases right.
More complex features like hoisting position absolute nodes and other layout features still take days to weeks of iterating to get something usable that isn't so fragile it'll blow up the next time you touch something.