title: ActiveRecord::RecordNotFound raises 404 instead of 500
body: <p>We had an action that was essentially failing silently in production because it was raising an <code>ActiveRecord::RecordNotFound</code> error, which Rails treats as a 404 error instead of a 500 error- meaning it wasn't being captured by our error logger.</p>
  
  <p>I don't like that Rails maps certain errors to 404s- I think it should be up to the developer to decide whether a URL is invalid, or whether the failure to retrieve an record is an application error. </p>
  
  <p>How do we ensure all Rails errors are treated as 500 errors?</p>