To support -DNO_ROOT work. The top-level installworld target creates a new METALOG starting with #mtree 2.0 so it needs to be first, to avoid overwriting installkernel METALOG entries.
I'm unsure which commit did it, but at a point near this commit the time taken by release builds drastically decreased. Before this close to 20 hours for an aarch64 cross-build, just over 6 after. Even though I can leave my build machine running, the decrease in latency is very nice. Thank you.