ack... ok, I think I might chalk this up to "user error"... but I guess other people could end up similarly confused. I have a bookmark for the site in mobile safari. I got the email magic-link delivered to my Gmail and it opened the site properly auth'd in the Gmail iOS web browser, not mobile Safari. If that's indeed what had been happening then I guess we wouldn't be surprised at the result that I'm not logged in on mobile Safari. But it's reasonable to consider other people may fall down this same path... is there a well-known solution to this kind of thing?