Thanks Brad for the implementation explanatin but I'd rather need a
document outlining the expectations for user-facing functionality.
I just had to separately and manually login three times (on Meta, then
on Wikipedia, then on MediaWiki.org
) in order to be logged in on most
wikis. I don't find any page explaining whether it's normal for global
login to require entering my password 3+ times. If it's expected and
documented, I can stop worrying.