If you edit a page for a long time and try to save, you will see a message saying "We could not process your edit due to a loss of session data. Please try again." (message session_fail_preview).
Does it really have to be this way? Simply re-saving almost always does the trick, so can the software just try to generate the token automatically?
(This might be a dupe because it's a very, very old and annoying issue, but I couldn't find another bug that asks about it.)
How long do tokens take to expire, anyway? And do Wikimedia settings differ from the defaults? @aaron, do you know?
We don't use the matchEditToken timestamp yet, so I guess that leaves $wgObjectCacheSessionExpiry (1 hour) and lastly $wgCookieExpiration (30 days).
wgObjectCacheSessionExpiry is kind of janky so I made https://gerrit.wikimedia.org/r/#/c/219227/ to reduce inconvenient expirations.
Is this deployed to production Wikipedia sites? If it is, it didn't remove the problem I was talking about.