This is a subtopic of this topic on navigation features.
This one is broken out for separate visibility because it appears to be an oversight or exceptional situation with respect to implementing the in-browser backward/forward swiping on the AndroidOS Discourse mobile ‘app’ (captive browser). This function is basic enough that it can be classified as a major omission and tantamount to a nuisance, non-critical bug.
According to this post, the iOS mobile app allows swiping left and right for back and forward history navigation. This is a fairly universal browsing and navigating behavior at this point (document viewers, photo viewers, etc.), so it seems worth some extra attention to overcome any remaining hurdles to implement it in AndroidOS.