I would expect that in the limit it would follow clean-room design (see https://en.wikipedia.org/wiki/Clean_room_design) -- you only have to do enough to prove to a court that you or someone you got to rewrite something according to your spec weren't sufficiently tainted by the original code to rise to copyright infringement (even if the result is bitwise identical due to primarily one obvious way to do it).

The GNU project offers a bit of guidance for what counts as "legally significant changes" to them: https://www.gnu.org/prep/maintain/maintain.html#Legally-Sign... They use about 15 lines rather than the GP's 10 lines, but point out there could be context where even many lines of repeated change (renaming a symbol) is not legally significant. My opinion is there's no hard line, like always you need to weigh the risk of getting sued (some contributors might even be unreachable or identifiable) against the cost of reimplementing even things legal counsel says are insignificant (at the end of which you still might get sued anyway and have to prove you did clean-room/changes were insignificant/it's fair use/whatever).

I honestly don't know, but I would have to imagine something like fixing typos would fall under "this is obvious" and you can't claim copyright on it. And likewise, if your algorithm that you contributed was obvious, it would fall under the same rule.

Note, I'm just speculating of course, but I do know changing license is something that does happen and I'm sure Minio is probably looking at getting people to sign off on previous contributions. And if they can't get the contributor's consent, will look at re-implementing things or just not use previous contributions, since it is possible that the previous contribution is no longer used.

> trivial changes there’s often no alternate implementation (e.g. correcting a typo)

IANAL, but simple changes like these likely don't meet the threshold of copyrightablity.