Function write_error_response_with_header 

pub async fn write_error_response_with_header(
    session: &mut Session,
    status_code: StatusCode,
    msg: String,
) -> Result<bool>

Write a plain-text HTTP error response to the downstream client.

Sets Content-Type: text/plain, X-Content-Type-Options: nosniff, and a custom Server header before sending msg as the response body.

Always returns Ok(true) so callers can do return write_error_response_with_header(…).await?; from within a request_filter implementation.