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Prerequisite for felhom-sshd (H1). Closes the SPIKE-felhom-sshd §8 lockout: a second sshd's RuntimeDirectory=sshd removed the SHARED /run/sshd privsep dir and took stock sshd on :22 down (sessions reset after KEXINIT). Host artifacts (configs/, installed by felhom-host-install): - felhom-privsep.tmpfiles: layer 1, boot-persistent /run/sshd owned by no unit - felhom-mgmt-watchdog.sh/.service/.timer: layer 2, AGENT-INDEPENDENT ~60s heal (stat-first recreate + reset-failed sshd only if failed + heal-marker); never RuntimeDirectory=, never restarts stock sshd, never touches a healthy dir. Go (internal/mgmtplane): read-only Reporter → additive omitempty mgmt_plane heartbeat stanza (privsep_dir_ok/sshd_reachable/healed_recently/privsep_healed_at), wired via Collector.SetMgmtPlaneReporter. Non-hollow tests + red-proofs. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6