Function spawn_with_callbacks 

pub async fn spawn_with_callbacks<A, B>(
    options: LaunchOptions,
    initialize: InitializeParams<A>,
    startup_deadline_unix_ms: u64,
    callbacks: Option<Arc<dyn CallbackHandler>>,
) -> Result<(ChildSession, InitializeResult<B>)>
where
    A: Serialize,
    B: DeserializeOwned,

As spawn, installing the handler for the callbacks this client advertised in client_methods (0.21+).