That's fair for a well-scoped subroutine: what I meant is that if you ask an agent to write a compiler and let it rip for a few days, you are going to be spending a few more days correcting the default behaviors in the distribution, which often do not tend towards hardware-oriented design.
To correct those behaviors, you're going to write tools and skills, and that's going to help, but it is still clear that you are fighting the distribution (today).
Yes, say "Build a compiler" will require you to clean up stuff if you leave the agent for days, but not because of the LLM or the quality of the tool, but because you hardly specified anything, so of course it's gonna make assumptions you need to correct.
If you instead spend a day writing a proper specification, then ask the agent to spend a week implementing that, you'll need zero tools and skills afterwards to clean it up, because there won't be any misunderstandings, assumptions or other things, just code fulfilling what the specification says.
Granted, this does require you to not use obviously dumb models, like anything you can run locally today, and at least within reasonable range of SOTA models. But they been able to do this for 6 months or more at this point.