Thanks for the responses, Brad. Is there some documentation somewhere for which modules are loaded by default and which ones aren't (e.g. mediawiki.api)?
Not that I know of, although I'm not terribly familiar with the details of ResourceLoader. It appears that the list is 'jquery' and 'mediawiki', but the latter module includes the mw.config and mw.user objects (and anything else in mediawiki.js[1] rather than a different file).