{ lib, modulesPath, flakeTarget, ... }:

let
  # Bakes this exact flake target's pre-generated SSH host key straight
  # into /etc/ssh/ -- mirrors modules/installer/host-keys.nix's
  # builtins.getEnv pattern (impure and empty under normal `nix
  # build`/`nix eval`, so this is a no-op unless explicitly opted into
  # with NIXOS_HOST_KEYS_DIR=... --impure), but places the key directly
  # rather than staging it under /etc/host-keys/ for a later manual copy
  # -- this is the whole system for a `lxc-*` host, built straight to a
  # pct-restorable tarball with no install step, so there's no later copy
  # step to stage for.
  #
  # Without this, config.system.build.tarball's built-in system just
  # generates a fresh host key at first boot like any other host would --
  # but sops-nix derives its decryption key from *this* file, and
  # .sops.yaml only trusts whatever key scripts/sync-host-keys.sh already
  # registered for this exact target name. A freshly-generated key can
  # never match that, so every secret (including this host's own login)
  # permanently fails to decrypt. Confirmed live: sops-install-secrets
  # errored with "Error getting data key: 0 successful groups required,
  # got 0" -- the container's actual host key's age fingerprint didn't
  # match the one registered in .sops.yaml at all.
  hostKeysDirStr = builtins.getEnv "NIXOS_HOST_KEYS_DIR";
  hasHostKeysDir = hostKeysDirStr != "" && builtins.pathExists hostKeysDirStr;
  hostKeysDir = /. + hostKeysDirStr;

  # flakeTarget ("${platform}-${buildType}") comes in via specialArgs from
  # flake.nix's mkTarget -- exactly the name scripts/sync-host-keys.sh
  # registers keys under. Deliberately not read back from
  # config.environment.etc."flake-target" (which is set to the same value)
  # -- this module also *contributes* to environment.etc below, and a
  # module reading the merged value of an option it's still defining is a
  # circular dependency (confirmed: "infinite recursion encountered").
  privKeyFile = hostKeysDir + "/${flakeTarget}_ssh_host_ed25519_key";
  pubKeyFile = hostKeysDir + "/${flakeTarget}_ssh_host_ed25519_key.pub";
  hasKeyForThisTarget =
    hasHostKeysDir
    && builtins.pathExists privKeyFile
    && builtins.pathExists pubKeyFile;
in
{
  # LXC containers share the host kernel — Proxmox starts them by exec'ing
  # /sbin/init directly, no bootloader/initrd involved — and Proxmox has its
  # own container hostname/network provisioning outside Nix. nixpkgs' own
  # virtualisation/proxmox-lxc.nix module already handles all of this
  # correctly (boot.isContainer, loader.initScript, systemd-networkd) and,
  # critically, provides config.system.build.tarball — a directly
  # `pct restore`-able container image, no nixos-install/bind-mount needed
  # (nixos-install refuses to touch the filesystem it's currently running
  # on, which is exactly what bind-mounting / onto /mnt for an installer
  # LXC container does).
  imports = [
    (modulesPath + "/virtualisation/proxmox-lxc.nix")
  ];

  proxmoxLXC = {
    # host.nix declares each host's real hostname (networking.hostName);
    # keep that instead of letting Proxmox's ambient container config win.
    manageHostName = true;
    # Unprivileged matches how these containers are actually created.
    privileged = false;
  };

  boot.loader = {
    grub.enable = false;
    systemd-boot.enable = false;
  };

  # NetworkManager depends on a running udevd to enumerate/classify devices,
  # which boot.isContainer disables (see nixpkgs' container-config.nix) —
  # that's what broke DHCP-hostname registration in Pi-hole. The imported
  # proxmox-lxc.nix module already switches networking to systemd-networkd
  # for the same reason; it just doesn't disable NetworkManager itself,
  # which modules/common/configuration.nix enables for every host.
  networking.networkmanager.enable = lib.mkForce false;

  environment.etc = lib.mkIf hasKeyForThisTarget {
    "ssh/ssh_host_ed25519_key" = {
      source = privKeyFile;
      mode = "0600";
    };
    "ssh/ssh_host_ed25519_key.pub" = {
      source = pubKeyFile;
      mode = "0644";
    };
  };
}