One of my biggest UX nits with Fly (I have no excuses, I have all the access I need to go fix this myself) is that we "kernel panic" when your entrypoint command fails. Of course, our kernel is not really panicking --- we've just run out of things for our `init` to manage, so it exits, and when pid 1 exits, so does the kernel. But you get the terrifying stack dump.
We can clean this up, so that you get a clearer, simpler error ("your entrypoint exited, here's the exit code, there's nothing else for this VM to do so it's exiting, have a nice day"), and it's been on the docket for months. We'll get it done!
We could conceivably add a flag for our `init` to hang around waiting for you to SSH in after your entrypoint exits. But that's clunky and complicated. Usually, you want your kernel to exit when your entrypoint fails, so that your service restarts! What you should do instead is push a container that has enough process supervision to hang around itself. Here's a doc: