according to raidz expansion feature by don-brady · Pull Request #15022 · openzfs/zfs · GitHub
“The pool remains accessible during expansion. Following a reboot or export/import, the expansion resumes where it left off.”
Of course, that’s kind of irrelevant as evidently, I’m in a weird state. Perhaps there’s a command that normally should be ran at the end of the process, which my reboot interrupted?