Great idea. Although... is there a point in archiving old, finalized sandbox posts? Otherwise I believe that the best solution would make it possible for the poster move the post between categories, from sandbox to live challenges.

I went ahead and proposed a move post between different categories feature request. It would be generally handy to have, I think.

Hey, since we already have a discussion on this, might as well continue it there.

I have suggested the "move post between categories" idea a number of times myself (long before Code Golf started on Codidact). However, I think there is educational benefit (especially for new people developing challenges) to seeing the comments associated with a Sandbox post. Those comments would be lost in a move - not inherently lost but rather because they would be deliberately deleted in favor of comments relating to the "active" challenge as opposed to the development of the challenge.

And now I see the funny part - my post Closed because it is a duplicate...of one of my own posts!