cosmic-greeter: add cosmic-randr to PATH; nixos/cosmic-greeter: install cosmic-comp by default (#448844)

nixos/modules/services/display-managers/cosmic-greeter.nix

@@ -24,6 +24,11 @@ in
   };
 
   config = lib.mkIf cfg.enable {
+    environment.systemPackages = [
+      pkgs.cosmic-comp
+      cfg.package
+    ];
+
     services.greetd = {
       enable = true;
       settings = {
@@ -50,14 +55,22 @@ in
       };
     };
 
+    systemd.tmpfiles.settings.cosmic-greeter."/run/cosmic-greeter".d = {
+      group = "cosmic-greeter";
+      mode = "0755";
+      user = "cosmic-greeter";
+    };
+
     # The greeter user is hardcoded in `cosmic-greeter`
     users.groups.cosmic-greeter = { };
     users.users.cosmic-greeter = {
       description = "COSMIC login greeter user";
       isSystemUser = true;
       home = "/var/lib/cosmic-greeter";
+      homeMode = "0750";
       createHome = true;
       group = "cosmic-greeter";
+      extraGroups = [ "video" ];
     };
     # Required for authentication
     security.pam.services.cosmic-greeter = { };