Ships failing to start with "disk: unknown epoch version"

[dosullivan]

We've seen a handful of ships on the Tlon Hosting platform have some issues with the new chop and roll setup. Sometimes the newest epoch doesn't have anything set inside its epoc.txt file; it's just an empty file.

We first run roll, and then run chop as part of scheduled maintenance on a ship.

In about ~10 ships now, when we run roll, the epoc.txt file in the latest epoch directory ends up with nothing written to it. The next time we try to start the ship, it crashes with this log, because the file is empty:

~
urbit 3.0
boot: home is /pier/<ship-name>
disk: unknown epoch version: '', expected '1'
upgrade runtime version
unable to open event log

If I go into .urb/log inside the pier and find the latest epoch, and then put in the 1 that vere is expecting, the ship then boots successfully.

[Tenari]

seems related: urbit/urbit#6989