Add Steam Deck (nix-deck) configuration with Jovian-NixOS and remote building

- Add Jovian-NixOS integration for Steam Deck hardware support
- Create nix-deck machine configuration with SteamOS role
- Add jovian-compat.nix for NixOS 25.05 compatibility (remove in 25.11+)
- Create remote-build role for distributed builds
- Configure zix790prors as build host
- Configure nix-book and nix-deck to use remote builder with fallback
- Add comprehensive setup documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

roles/default.nix

@@ -12,6 +12,7 @@ with lib;
     ./nfs-mounts
     ./nvidia
     ./printing
+    ./remote-build
     ./spotifyd
     ./users
     ./virtualisation

roles/desktop/default.nix

@@ -23,5 +23,6 @@ with lib;
     ./kde.nix
     ./programs.nix
     ./sddm.nix
+    ./steamos.nix
   ];
 }

roles/desktop/steamos.nix

@@ -0,0 +1,47 @@
+{ lib, config, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.roles.desktop;
+in
+{
+  options.roles.desktop.steamos = {
+    enable = mkEnableOption "SteamOS (Jovian) configuration";
+
+    autoStart = mkOption {
+      type = types.bool;
+      default = false;
+      description = "Automatically start Steam Deck UI on boot";
+    };
+
+    user = mkOption {
+      type = types.str;
+      default = "johno";
+      description = "User to run Steam as";
+    };
+
+    desktopSession = mkOption {
+      type = types.nullOr types.str;
+      default = null;
+      description = "Desktop session to launch when switching to Desktop Mode";
+    };
+
+    enableDeckyLoader = mkOption {
+      type = types.bool;
+      default = true;
+      description = "Enable Decky Loader plugin system";
+    };
+  };
+
+  config = mkIf (cfg.enable && cfg.steamos.enable) {
+    jovian.steam = {
+      enable = true;
+      autoStart = cfg.steamos.autoStart;
+      user = cfg.steamos.user;
+      desktopSession = cfg.steamos.desktopSession;
+    };
+
+    jovian.decky-loader.enable = cfg.steamos.enableDeckyLoader;
+  };
+}

roles/jovian-compat.nix

@@ -0,0 +1,43 @@
+{ lib, config, ... }:
+
+# Compatibility shim to provide services.logind.settings for NixOS 25.05
+# This allows Jovian-NixOS to work with stable NixOS
+# REMOVE THIS FILE when upgrading to NixOS 25.11 or later
+
+with lib;
+
+let
+  nixosVersion = config.system.nixos.release;
+  isCompatibleVersion = versionOlder nixosVersion "25.11";
+in
+{
+  options.services.logind.settings = mkOption {
+    type = types.attrsOf (types.attrsOf types.anything);
+    default = {};
+    description = "systemd-logind configuration. See logind.conf(5) for available options.";
+  };
+
+  config = mkMerge [
+    {
+      assertions = [
+        {
+          assertion = isCompatibleVersion;
+          message = ''
+            The Jovian compatibility shim (roles/jovian-compat.nix) is only needed for NixOS 25.05 and earlier.
+            You are running NixOS ${nixosVersion}.
+            Please remove 'roles/jovian-compat.nix' from your flake.nix imports.
+          '';
+        }
+      ];
+    }
+    (mkIf (config.services.logind.settings != {}) {
+      # Convert the settings to extraConfig format for older NixOS
+      services.logind.extraConfig = let
+        mkSection = section: settings:
+          "[${section}]\n" +
+          (concatStringsSep "\n" (mapAttrsToList (k: v: "${k}=${toString v}") settings));
+      in
+        concatStringsSep "\n\n" (mapAttrsToList mkSection config.services.logind.settings);
+    })
+  ];
+}

roles/remote-build/default.nix

@@ -0,0 +1,127 @@
+{ lib, config, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.roles.remote-build;
+in
+{
+  options.roles.remote-build = {
+    enableBuilder = mkOption {
+      type = types.bool;
+      default = false;
+      description = "Enable this machine as a remote build host for other machines";
+    };
+
+    builderUser = mkOption {
+      type = types.str;
+      default = "nix-builder";
+      description = "User account for remote builders to connect as";
+    };
+
+    builders = mkOption {
+      type = types.listOf (types.submodule {
+        options = {
+          hostName = mkOption {
+            type = types.str;
+            description = "Hostname or IP address of the build machine";
+          };
+
+          systems = mkOption {
+            type = types.listOf types.str;
+            default = [ "x86_64-linux" ];
+            description = "Supported systems";
+          };
+
+          maxJobs = mkOption {
+            type = types.int;
+            default = 8;
+            description = "Maximum number of parallel build jobs";
+          };
+
+          speedFactor = mkOption {
+            type = types.int;
+            default = 2;
+            description = "Speed factor compared to local building (higher = prefer remote)";
+          };
+
+          supportedFeatures = mkOption {
+            type = types.listOf types.str;
+            default = [ "nixos-test" "benchmark" "big-parallel" "kvm" ];
+            description = "Supported build features";
+          };
+
+          sshUser = mkOption {
+            type = types.str;
+            default = "nix-builder";
+            description = "SSH user for connecting to the builder";
+          };
+
+          sshKey = mkOption {
+            type = types.nullOr types.path;
+            default = null;
+            description = "Path to SSH private key for authentication";
+          };
+        };
+      });
+      default = [];
+      description = "List of remote build machines to use";
+    };
+
+    fallbackToLocalBuild = mkOption {
+      type = types.bool;
+      default = true;
+      description = "Fallback to local building if remote builders are unavailable";
+    };
+  };
+
+  config = mkMerge [
+    # Builder host configuration
+    (mkIf cfg.enableBuilder {
+      # Create dedicated builder user
+      users.users.${cfg.builderUser} = {
+        isSystemUser = true;
+        group = cfg.builderUser;
+        description = "Nix remote build user";
+        home = "/var/lib/${cfg.builderUser}";
+        createHome = true;
+        shell = pkgs.bashInteractive;
+        openssh.authorizedKeys.keyFiles = [];  # Will be populated by client machines
+      };
+
+      users.groups.${cfg.builderUser} = {};
+
+      # Allow builder user to perform builds
+      nix.settings.trusted-users = [ cfg.builderUser ];
+
+      # Allow remote builds
+      services.openssh.enable = true;
+
+      # Ensure nix-daemon is accessible
+      nix.settings.allowed-users = [ "*" ];
+    })
+
+    # Client configuration (machines using remote builders)
+    (mkIf (cfg.builders != []) {
+      nix.buildMachines = map (builder: {
+        hostName = builder.hostName;
+        systems = builder.systems;
+        maxJobs = builder.maxJobs;
+        speedFactor = builder.speedFactor;
+        supportedFeatures = builder.supportedFeatures;
+        sshUser = builder.sshUser;
+        sshKey = builder.sshKey;
+      }) cfg.builders;
+
+      nix.distributedBuilds = true;
+
+      # Use substitutes from remote builders
+      nix.extraOptions = ''
+        builders-use-substitutes = true
+      '';
+
+      # Fallback to local build if remote unavailable
+      nix.settings.fallback = cfg.fallbackToLocalBuild;
+    })
+  ];
+}