And this is a flaw of Perforce: in a Git/Mercurial system, the presubmit can stack the changes into two commits. In P4, one CL has to contain both changes.

And Google uses P4(ish) because monorepo, so they build further abstractions over P4 to enable git and hg in user space which erases most of the potential benefits of either which is also all really, really good software, but it’s all effort necessitated by monorepo. CitC is a work of art, but it is also something necessitated by a stack of other choices that forced their hand into inventing something miraculous to keep hacking around a previous limitation that nobody else has.