The host layer's reboot-needed run is cut at the host's last boot (crash guard
last_boot_at, one minute skew margin): the kernel step's reboot is reported on the
kernel layer, so the flag outlived it until the next night. Feeds the System page
and the 14-day alarm. Test TestRebootNeeded_ClearedByAHostBootAfterTheClaim, red on
two mutants.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS