For me writing manpages as a spec worked well. While the format is unintuitive and tedious (at least to me), I used AI to format the manpages from my descriptions and rendered to PDF to review. Though it's been mainly useful for CLI utilities.
Once I got the manpages ready and the way I wanted, I just stored those in an empty project folder and told the agent to implement as specified in a language of my choosing.
Maybe for other development scenarios like GUI there is some "native" way to spec the project in a common format like this.