Considered breaking change because JSON serialization will change, and JSON is used quite often.

Reordering fields without changing their ID is indeed a non-breaking change from what I understand, albeit quite a useless one :)

Depends, if you use textproto then renaming is problematic too

Shit, you're right, I'm trying to remember the one that used to trip us up all the time, maybe it was removing fields?

There was definitely one that kept tripping up the checks and it was something people like to do.