Power loss while performing an update

[Wolfgang Tolkien]

Another snappy newbie question:

One of the obvious selling points of snappy is the ability to rollback 
to previous versions and the a/b partition scheme to safeguard core 
system updates.

My question is: do these built-in safety mechanism cover power losses at 
any time during the upgrade process? For the core as well as for 
frameworks and apps? This is important for embedded devices, in 
particular those in remote locations or in vehicle installations where 
the driver may just shut off the car or truck at the worst possible time.

Ideally the system would automatically revert to the previous known 
working core/framework/app revision in case of an update failure.

I read the description at

https://developer.ubuntu.com/en/snappy/guides/system-updates/

and it sounds like this feature is already there for the core. But how 
about frameworks and apps? I assume the system simply wouldn't switch 
over to the newer version if the upgrade process is not completed, is 
that correct? Is there any point in time where a power loss would still 
be fatal?

Thanks,
Wolfgang