Add `modules.storage.zfs`, the host-level pool import: a host declares its ZFS
host id and the pools to import with their dataset mountpoints, and the module
imports those pools as durable state rather than recreating them, so a
service's data survives any rebuild or reimage.
Add a shared `storage` group with a fixed gid to the base config both the host
base and the guest-base build on, so a host and every guest carry the same
number and an identity-mapped container write lands on the pool as that group
without per-service permission juggling.
No host enables the module: the only host is a laptop with no pools and a
kernel with no ZFS build, so the enabled build was verified by ad-hoc
enablement against a ZFS-supported kernel while the committed tree stays inert.
Add a third auto-loaded kind beside the host and the module: the guest, a
reusable definition under guests/ that a host enables like a module and that
realizes its interior as a systemd-nspawn nested container.
Split the shared base config so a guest can stand on it.
base.nix now holds the substrate both bases share — the primary user,
home-manager, and the unstable/stable overlays.
system.nix keeps the host-only machinery, and a new guest.nix is the slim
guest-base: it imports the full modules tree, pins the interior release, and
auto-enables the toolkit bundle and SSH so any guest is workable on sight.
Give modules.ssh a guest flavor.
A host restores its host keys from secrets as before, while a guest sets
hostKeys.restore = false, names no sops files, and self-generates a host key,
so it holds no age key of its own.
The lib grows a guest helper that declares the guests.<path> namespace with an
enable and a backend field.
Only the container backend is built; microvm is a reserved value that trips a
clear build-time assertion rather than silently building nothing.
A sample guest exercises the whole path, and neogaia enables it, so the guest
interior builds through the existing nix flake check seam.
