shoe: improve +on-load logic
shoe: improve +on-load logic

Turns out that if we use a tag we can just check the value without
needing vase operations.

ngzax/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,urbit/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit