I haven’t ever setup a Discourse forum, so I don’t know how feasible the following is.
If you cut and paste the url shown in the navigation bar (starting with www.codingame.com/forum) into a post, it shows up with a preview of the CG homepage. See:
This is because the www.codingame.com/forum address is just a redirect to the actual home of the forum, which is at forum.codingame.com. Here is a link using that URL:
Notice how much nicer that is! Unfortunately, most people use the www… links, and so a major feature of Discourse is subverted. It would be nice if this could be somehow fixed.