Function encode_user_prompt 

pub fn encode_user_prompt(
    prompt: &str,
    session_id: &str,
    uuid: &str,
) -> Result<String, Error>

Encode a user prompt as one line of stream-json input.

Returns a string terminated by \n suitable for writing directly to the subprocess’s stdin.

uuid is the prompt’s own id, and it is stamped on every frame: the CLI emits that prompt’s command_lifecycle frames (queued, started, …) only when the frame carries one (measured: zero frames without), and a reused id makes the CLI drop the prompt outright with no error anywhere. Mint a fresh one per send (crate::request_id::next_prompt_id).

Errors

Error::MessageParse wrapping a JSON serialization failure (extraordinarily rare for string inputs; included for totality).