For one developer, the device never disappears, even when the data disk
is prepared; it's unclear whether this is always true on Linux.

If called too early the run will fail.  Ideally, we'd know of a specific
marker that the device is ready to run...

The message on the Playdate screen isn't as clear as it could be for
newer developers.  A message from crank makes it clearer that we're
waiting for their action.

On Mac, and presumably Windows, Data Disk mode is exited automatically
when the Playdate is ejected.