seatd: pull the service definition into my own repo

this will allow me to configure the package

hosts/common/programs/seatd.nix

@@ -1,12 +1,26 @@
-{ ... }:
+{ config, lib, ... }:
 let
   cfg = config.sane.programs.seatd;
 in
-{
-  sane.programs.seatd = {};
+lib.mkMerge [
+  {
+    sane.programs.seatd = {};
+  }
+  (lib.mkIf cfg.enabled {
+    users.groups.seat = {};
 
-  # TODO: sandbox seatd
-  # also consider any alternatives (ConsoleKit?).
-  # /run/seatd.sock location can be configured, but only via compile-time flag
-  services.seatd.enable = lib.mkIf cfg.enabled true;
-}
+    # TODO: /run/seatd.sock location can be configured, but only via compile-time flag
+    systemd.services.seatd = {
+      description = "Seat management daemon";
+      documentation = [ "man:seatd(1)" ];
+
+      wantedBy = [ "multi-user.target" ];
+      restartIfChanged = false;
+
+      serviceConfig = {
+        Type = "simple";
+        ExecStart = "${cfg.package}/bin/seatd -g seat";
+      };
+    };
+  })
+]