Greeter freezes if the persistent filesystem is corrupted
If the user attempts to mount the persistent filesystem from the greeter UI and it happens to be corrupted, the attempting-to-mount animation never goes away, and the "Start Tails" button stops working. There are no errors and it is not apparent to the user why it's stuck. After that, the user has no choice but to to hard-reboot the system since the OS won't load.
I've seen this happen on two separate occasions, probably because the OS was not properly flushing its caches on shutdown (which may be a separate issue) or because the thumb drive was somehow malfunctioning. In both cases, after I rebooted and logged in without mounting persistent storage up front, I could unlock the partition using the "Disks" app with no errors, but the underlying partition was displayed as "Unknown" (rather than "ext4") and I had to run fsck to repair it.
Instead of freezing, the UI should attempt to unlock the filesystem and, if the filesystem is unlocked but can't be mounted, display an error advising the user that the filesystem may be corrupted.