Type Alias MessageCallback 

pub type MessageCallback = Arc<dyn Fn(Message) -> Option<Message> + Send + Sync>;

Optional callback invoked for each message received from the CLI.

• Return Some(msg) to pass the message through (possibly transformed).
• Return None to filter the message out of the stream.

When no callback is configured, all messages pass through unchanged.

Aliased Type

pub struct MessageCallback { /* private fields */ }