> Jevons’. Jevons’ paradox predicts that when something becomes cheaper, demand increases as the cheaper good is economically viable in a wider variety of cases.

That's just the usual behavior of any market. When prices go down, demand goes up.

Jevon's paradox specifically says when prices go down by a factor of x, demand goes up by a factor greater than x, leading to total consumption (measured in money spent) goes up.

In the context of this post we can paraphrase (replacing money with programmers) like so:

Once AI makes it so developing any piece of software takes half as many programmers, the amount of software developed will go up by more than two times, leading to a net increase in the number of programmers required.