title: Background Execution doesn't work as expected, closing tab and reopening results in dead connection
body: <p>How does Pro+ background execution work?</p>
  <p>I upgraded from pro for background execution, do I have to turn it on somehow?
  It doesn't seem to work. I'm very diligent in not wasting resources (use cpu when no gpu is needed, turn off while editing) and I use it the same amount as in pro without hitting the resource limits.</p>
  <p>But when I close the tab for like 1 hour when i'm away while executing when I come back it says the runtime is still on, I only get connecting... though, when I try to run a cell I get a disconnected error. In Manage runtimes it shows as running.
  But after it doesn't, my saves (to drive) are not saved.</p>
  <p>The runtimes disk is visible on the right, with files there too, when I try to save some (checkpoints pytorch lightning) it gets an error.
  I'm so confused.</p>
  <p>thanks for any help, the documentation do not mention how to set up background execution in detail, just that it's there.</p>