How to specific the kernel snap on core18

Option 1 looks the cleanest. Option 2 feels like an unusual spelling of a channel, where the track usually precedes the risk but in this case is succeeding a snap name.

Seems reasonable to have that. We just need to watch out for the points above: once we allow tracks to be specified, they need to be respected. Otherwise we’ll open a gap and will be locked out into a backward compatibility issue.