Function stream_to_stdout 

pub async fn stream_to_stdout<R>(
    stream: &mut StreamingResult<R>,
) -> Result<PromptResponse, Error>

Helper function to stream assistant-visible completion output to stdout.

This helper prints streamed assistant text and reasoning. Streaming metadata events, such as MultiTurnStreamItem::CompletionCall, are not printed; metadata is returned on the PromptResponse via accessors such as PromptResponse::completion_calls. A model-turn retry prints a visible boundary because text already written to stdout cannot be retracted.