Function invoke_complete_frame 

pub fn invoke_complete_frame(
    error_code: Option<&str>,
    error_details: Option<&str>,
    log_result_b64: &str,
) -> Vec<u8> 

Build the terminal InvokeComplete event frame. error_code / error_details are None on success; log_result_b64 is the base64-encoded last 4 KiB of the function’s tail log (empty string when no log was captured).