[qalmakka]

> I'm not sure though relicensing MIT code under AGPL is legally sound if your additions are just bug fixes.

It is: the original unmodified code is still MIT, but the bits you wrote and thus you hold the copyright for are AGPL. The combination of your bits + old bits is AGPL; some judge may argue your derived work isn't derived enough if you just change a few characters though. Still, I may argue that fixing a bug, no matter how trivial, requires you to perform a creative task, which almost definitely is by itself to be considered enough to go above the threshold required by a derived work.

[eqvinox]

It really doesn't matter until one tries to enforce an AGPL provision. If you do, that's where as you say will be arguments whether one added something substantial enough; basically the AGPL terms can really only be enforced on those additions.