observe-hook: compiles
+$ card card:agent:gall
+$ versioned-state
$% state-0
- state-0
+ state-1
==
::
+$ serial @uv
%1 `this(state old-state)
::
%0
- =. this(state [%1 observers.old-state])
+ =. state [%1 observers.old-state]
%+ on-poke
%observe-action
!> ^- action:sur
