Is this the hypothetical situation of someone doing an interactive rebase on public/published branches and making changes midway through? My current understanding is that, although it is possible, the community avoids doing that (policy: published code history set in stone). That style requires strong communication between developers. It makes people do extra investigation and work, and we all hate doing extra work, right? :)

I cannot speak for what they really do over at kernel.org, but if they do rebase their public repositories often (which will break people doing pushes and fetch/merges without some regular communication), yes, it is possible to sneak something in because the public rebase will not be as exceptional.

This is where you tell me that's what they do there and make me scared again. ;)