I think it is worth adding a boolean variable wgPostEdit, which is true if and only if the user just saved the article.
Right now, this is implemented in https://www.mediawiki.org/wiki/Extension:PostEdit , but the real point of the extension is to show a visual notification. Other extensions ideally shouldn't have to depend on all that just to get a boolean. E3Experiments currently uses it implicitly (I will temporarily make it an explicit dependency), and I'm sure there are other extensions and gadgets that could use it.
It looks like this could maybe be implemented in attemptSave, but I'm open to suggestions.