The early before_build resume ran for Windows sets too. The fleet restart skips only what the
POSIX pause restarted (already_restarted), so a Windows gateway resumed before the build was
then drained and restarted a second time by the fleet pass: one extra outage per update that
main never had. The early resume is now POSIX-only and goes through the main facade like every
other resume call; Windows resumes where it always did. Docs say so.
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