feat: Tier 1 system features — snapper, hibernate, containers, libvirt, keyring

Five opt-in modules lifted from bernardo/nixos and adapted to Nomarchy's
nomarchy.system.* option namespace. All default off (except keyring which
defaults on); evaluation of the existing VM/ISO is unchanged when the
toggles are unset.

- core/system/snapper.nix: BTRFS timeline snapshots (5h/7d), nixos-rebuild-snap
  wrapper that pre-snaps before each switch using the running hostname.
  Auto-skips when / isn't BTRFS so impermanence/non-BTRFS hosts are safe.
- core/system/hibernate.nix: suspend-then-hibernate on lid/idle/power-key
  with configurable idleMinutes (default 30). Description warns swap is
  required.
- core/system/containers.nix: rootless Podman with dockerCompat + dns +
  podman-compose, podman-tui, dive. Better default than the docker daemon
  for a desktop distro.
- core/system/virtualization.nix: extends the existing uwsm/Hyprland file
  with a libvirt + virt-manager + OVMF branch behind
  nomarchy.system.virtualization.libvirt.enable.
- core/system/pam.nix: GNOME Keyring auto-unlock at SDDM/login/hyprlock
  plus gcr-ssh-agent so SSH keys flow through the keyring instead of a
  separate ssh-agent. Default on.
- core/system/options.nix: declares the five new options.
- core/system/default.nix: imports the four new files.
- installer/install.sh: surfaces all five toggles as commented one-liners
  in the "Optional Nomarchy modules" section of the generated system.nix.
  Verified via the existing dry-run / generator smoke test.

Verified each toggle lights up the right NixOS option (services.snapper,
logind IdleAction, virtualisation.podman/libvirtd, pam.sddm.enableGnomeKeyring)
via nix eval against extendModules. VM and live-ISO toplevels still build.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

core/system/containers.nix

@@ -0,0 +1,23 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.nomarchy.system.containers;
+in
+{
+  config = lib.mkIf cfg.enable {
+    virtualisation.podman = {
+      enable = true;
+      # `docker` and `docker-compose` invocations transparently route to
+      # podman. Pairs cleanly with rootless mode.
+      dockerCompat = true;
+      defaultNetwork.settings.dns_enabled = true;
+    };
+
+    environment.systemPackages = with pkgs; [
+      podman
+      podman-compose
+      podman-tui
+      dive
+    ];
+  };
+}

core/system/default.nix

@@ -18,6 +18,11 @@
     ./impermanence.nix
     ./browser.nix
     ./makima.nix
+    # Tier 1 system features (all opt-in via nomarchy.system.*).
+    ./snapper.nix
+    ./hibernate.nix
+    ./containers.nix
+    ./pam.nix
     ../../themes/engine/plymouth.nix
     ../../themes/engine/sddm.nix
   ];

core/system/hibernate.nix

@@ -0,0 +1,24 @@
+{ config, lib, ... }:
+
+let
+  cfg = config.nomarchy.system.hibernation;
+in
+{
+  config = lib.mkIf cfg.enable {
+    # Wait this long after suspend before hibernating, and use the same
+    # delay as the idle-action timeout so the two paths agree.
+    systemd.sleep.extraConfig = ''
+      HibernateDelaySec=${toString (cfg.idleMinutes * 60)}
+    '';
+
+    services.logind = {
+      settings.Login = {
+        HandleLidSwitch = lib.mkDefault "suspend-then-hibernate";
+        HandleLidSwitchExternalPower = lib.mkDefault "suspend";
+        HandlePowerKey = "hibernate";
+        IdleAction = "suspend-then-hibernate";
+        IdleActionSec = toString (cfg.idleMinutes * 60);
+      };
+    };
+  };
+}

core/system/options.nix

@@ -51,5 +51,56 @@
       default = "summer-night";
       description = "Selected system theme.";
     };
+
+    # ----- Tier 1 system features (all opt-in, no behavioural change off) ---
+
+    snapper = {
+      enable = lib.mkEnableOption ''
+        Snapper-driven BTRFS timeline snapshots of `/`. Auto-disables when
+        `/` isn't BTRFS. Includes a `nixos-rebuild-snap` wrapper that takes
+        a "Pre-rebuild" snapshot before each switch.
+      '';
+    };
+
+    hibernation = {
+      enable = lib.mkEnableOption ''
+        suspend-then-hibernate (lid close, idle, power button). NOTE: this
+        requires a disk swap device or swapfile sized to at least RAM —
+        zRAM alone is not enough.
+      '';
+      idleMinutes = lib.mkOption {
+        type = lib.types.int;
+        default = 30;
+        description = "Idle minutes before suspend-then-hibernate fires.";
+      };
+    };
+
+    containers = {
+      enable = lib.mkEnableOption ''
+        Rootless Podman with Docker compatibility (`docker` → `podman`),
+        plus podman-compose, podman-tui and dive.
+      '';
+    };
+
+    virtualization = {
+      libvirt = {
+        enable = lib.mkEnableOption ''
+          libvirt daemon + virt-manager + OVMF. The user must be in the
+          `libvirtd` group.
+        '';
+      };
+    };
+
+    keyring = {
+      enable = lib.mkOption {
+        type = lib.types.bool;
+        default = true;
+        description = ''
+          Auto-unlock GNOME Keyring at SDDM/Hyprland login and route SSH
+          keys through `gcr-ssh-agent`. Default on — near-universal QoL
+          improvement.
+        '';
+      };
+    };
   };
 }

core/system/pam.nix

@@ -0,0 +1,28 @@
+{ config, lib, ... }:
+
+let
+  cfg = config.nomarchy.system.keyring;
+in
+{
+  config = lib.mkIf cfg.enable {
+    # Auto-unlock GNOME Keyring at SDDM autologin and at login. hyprlock
+    # gets the same treatment so the session keyring stays unlocked when
+    # the screen lock disengages.
+    security.pam.services = {
+      login.enableGnomeKeyring = true;
+      sddm.enableGnomeKeyring = true;
+      hyprlock.enableGnomeKeyring = true;
+    };
+
+    # Run the keyring + the gcr SSH agent. Disabling `programs.ssh.startAgent`
+    # ensures keys flow through the keyring's agent (so unlock-on-login
+    # carries over to ssh) instead of a separate ssh-agent process.
+    services.gnome.gnome-keyring.enable = true;
+    services.gnome.gcr-ssh-agent.enable = true;
+    programs.ssh.startAgent = lib.mkForce false;
+
+    # Point downstream tooling at the gcr socket so `ssh` / `git` / etc.
+    # find the keyring's keys without per-user shell config.
+    environment.sessionVariables.SSH_AUTH_SOCK = "$XDG_RUNTIME_DIR/gcr/ssh";
+  };
+}

core/system/snapper.nix

@@ -0,0 +1,42 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.nomarchy.system.snapper;
+  rootIsBtrfs = (config.fileSystems."/".fsType or "") == "btrfs";
+  active = cfg.enable && rootIsBtrfs;
+in
+{
+  config = lib.mkIf active {
+    # `nixos-rebuild-snap`: take a Snapper pre-rebuild snapshot, then run
+    # `nixos-rebuild switch` against the current host. The hostname is read
+    # from the running config so this script works on every machine without
+    # editing.
+    environment.systemPackages = [
+      (pkgs.writeShellScriptBin "nixos-rebuild-snap" ''
+        if [ "$(id -u)" -ne 0 ]; then
+          echo "This script must be run as root (use sudo)" >&2
+          exit 1
+        fi
+        echo "Creating pre-rebuild snapshot..."
+        ${pkgs.snapper}/bin/snapper -c root create \
+          -d "Pre-rebuild $(date +'%Y-%m-%d %H:%M:%S')" \
+          --cleanup-algorithm number
+        echo "Rebuilding..."
+        nixos-rebuild switch --flake .#${config.networking.hostName} "$@"
+      '')
+    ];
+
+    services.snapper.configs = {
+      root = {
+        SUBVOLUME = "/";
+        TIMELINE_CREATE = true;
+        TIMELINE_CLEANUP = true;
+        TIMELINE_LIMIT_HOURLY = "5";
+        TIMELINE_LIMIT_DAILY = "7";
+        TIMELINE_LIMIT_WEEKLY = "0";
+        TIMELINE_LIMIT_MONTHLY = "0";
+        TIMELINE_LIMIT_YEARLY = "0";
+      };
+    };
+  };
+}

core/system/virtualization.nix

@@ -1,6 +1,11 @@
-{ lib, ... }:
+{ config, lib, pkgs, ... }:
 
+let
+  libvirt = config.nomarchy.system.virtualization.libvirt.enable;
+in
 {
+  # uwsm + Hyprland session — present on every Nomarchy install regardless
+  # of the optional libvirt branch below.
   programs.uwsm = {
     enable = lib.mkDefault true;
     waylandCompositors.hyprland = {
@@ -8,4 +13,14 @@
       prettyName = "Hyprland";
     };
   };
+
+  # Optional: libvirt + virt-manager + OVMF. Toggle with
+  # `nomarchy.system.virtualization.libvirt.enable = true;`. The user must
+  # be in the `libvirtd` group to drive virsh / virt-manager.
+  virtualisation.libvirtd.enable = lib.mkIf libvirt true;
+  environment.systemPackages = lib.mkIf libvirt (with pkgs; [
+    virt-manager
+    qemu
+    OVMF
+  ]);
 }