static CLI = Lazy::new(Cli::parse);

pub enum Command {
   // ...
 
  // not sure if Clap allows to do Server(SomeStruct) because it would be better than the ServerArgs below
  Server { 
    #[command(flatten)]
    server_args: ServerArgs, // current content of Command::Server { ... } 
    
    #[clap(ignore)]
    server_config: OnceCell<Config>,
  }
}

impl Cli {
  pub fn server_config(&self) -> &'static Config {
    let Command::Server { server_args, server_config } = self.command else { panic!("server_config() called outside server command code"); };
    server_config.get_or_try_init(|| Config::load(server_args)).expect("failed to load server config")
  }
}

fn main() {
  // ...
  match &CLI.command {
      // ...
     // current form
     Commands::Server(_) => {
       let server_config = CLI.server_config();

     // or if Commands::Server contained a tuple struct (see comment above)
     Commands::Server(server_args) => {
       let server_config = server_args.server_config();
       // ...