Sub-project 3 of the mesh-hardening follow-on. Accepts the single off-site coordinator as a documented availability SPOF (R8 + ADR-016 amendment) given the narrow blast radius (LAN/intra-cluster/local traffic unaffected; only remote relayed mesh access breaks). Hardens the one real gap: a base mesh coordinator-FQDN /etc/hosts pin so managed hosts survive a local-DNS hiccup. Coordinator off-site backup explicitly deferred to an ADR-022 kickoff (no throwaway infra).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
