Ship policy.hujson (mounted + installed on first deploy, edits preserved) and wire policy.mode=file / policy.path in config.yaml. Translate the Tailscale "grants" default into headscale's legacy "acls" format (self-access, tag:shared, Tailscale SSH), since headscale 0.28 doesn't support grants. Embed in deploy.sh and document `headscale policy check`.