clay: give %u answer for non-existent desks
Instead of considering it "in the future", an existence check for paths
on non-existent desks now always produce false.
++ read-u
|= [yon=aeon pax=path]
^- (unit (unit (each [%flag (hypo ?)] lobe)))
+ :: if asked for version 0, that never exists, so always give false
+ ::
+ ?: =(0 yon)
+ ``[%& %flag -:!>(*?) |]
:: if asked for a future version, we don't have an answer
::
?~ tak=(~(get by hit.dom) yon)
