AFAIU there's no obligation to contribute upstream at all, just the need to provide the source such that anyone who wants to can contribute upstream. So you can

AFAIU there's no obligation to contribute upstream at all, just the need to provide the source such that anyone who wants to can contribute upstream. So you can't grab the code in your SaaS and extend it without making it available to the public. For example the Truth Social was briefly in violation of AGPL when they took and adapted the Mastodon source code. Later on they provided a zip-file with the codes in it.