ObservedDoc's validated twin for the instance stream: the observer
maps every emission through the engine's read discipline, so a resolved
doc is a real WorkflowInstance. Model-gate and shape failures use
the enclosing ObserverState's invalid branch.
ObservedDoc's validated twin for the instance stream: the observer maps every emission through the engine's read discipline, so a resolved doc is a real WorkflowInstance. Model-gate and shape failures use the enclosing ObserverState's
invalidbranch.