anchor.diff:  
     config = mkIf cfg.enable {
   
  -    users.extraGroups.hydra = { };
  +    users.extraGroups.hydra = {
  +      gid = config.ids.gids.hydra;
  +    };
   
       users.extraUsers.hydra =
         { description = "Hydra";
  
positive.code:         createHome = true;
          home = baseDir;
          useDefaultShell = true;
        };
  
      users.extraUsers.hydra-queue-runner =
  
negative.code:         group = "hydra";
          useDefaultShell = true;
          home = "${baseDir}/queue-runner"; # really only to keep SSH happy
          uid = config.ids.uids.hydra-queue-runner;
        };
  
      users.extraUsers.hydra-www =
        { description = "Hydra web server";
          group = "hydra";
          useDefaultShell = true;
          uid = config.ids.uids.hydra-www;
        };
  
      nix.trustedUsers = [ "hydra-queue-runner" ];
  