This is something I could have sworn was reported previously, but I cannot find the bug for it.
Going to en.m.wikipedia.org from a desktop browser stays on the mobile site rather than redirecting back to the desktop version. This makes it extraordinarily inconvenient when somebody shares a mobile link and a desktop user follows it.
This also breaks the functionality in Google Chrome Mobile where you can check "Request desktop version".
Right now, Varnish checks whether user agent is mobile and then redirects to the mobile domain. We'd need to do something in the opposite direction.
This requires adding Varnish redirection to every mobile page view.
Varnish would need to run the same regular expression we use to detect mobile on the user agent on urls coming into the mobile domain and negate the result.
Not sure how practical this is and whether a performance issue since it would impact all page views.
Not been prioritised so haven't investigated.
Many people intentionally use the mobile site so we'd need to consider those users.
The mobile redirect code is here:
It seems "request desktop site" doesn't set any headers - all it does it set the user agent to a desktop user agent, so we can't explicitly distinguish users who have clicked "request desktop site" and users who want to to view mobile domain on desktop :-(