title: How to reconnect a returning client (web page) in socket.io to a previously started backend process
body: <p>Here's the use case I am trying to solve for: A user submits a form to a long running server-process. That process uses socket.io to report back to the browser the current status of the long-running process (step 1...step 2...step 3...).</p>
  
  <p>NOW, the user closes their browser, goes away, and comes back 2 minutes later. The long-running process is still working in the background, but now the client socket.io connection knows thinks a new sessions as begun.</p>
  
  <p>I can of course detect this situation on the backend, where I just end that request and tell the user to come back later (crappy solution), but I would really like to re-establish the socket.io connection with old long-running process if it is still running, or even if I am thinking about this in the right way. But I have to be able to support the user breaking the client connection and coming back later.</p>