If my employer were to offer permanent remote (in writing), I'd list my house and move out of the Bay Area that minute. It's literally the only thing keeping me in this expensive pit.

You've got to get it in writing though, as you say the policy could be changed on a whim and then you're stuck! Also, I wouldn't trust a recruiter who promised WFH unless they promised it in writing. Recruiters can say whatever nonsense they want in order to convince you to join, and then once you do, it's "oopsie! I was totally wrong about that whole WFH thing. Please report to your office building on Monday!"