Function write_result_json 

pub async fn write_result_json(
    attempt_dir: &Path,
    task_id: &str,
    agent_name: &str,
    model_name: Option<&str>,
    exit_code: i32,
    new_attempts: u32,
    parse_result: &Result<ParsedResponse, AgentError>,
    raw_stdout: &str,
    raw_stderr: &str,
)

Write a structured result.json to the attempt directory for debugging.