Raised when workflow code swallows Continuum's suspend control throw.

The engine suspends a workflow by throwing a control tuple after the pending effect has been journaled. A user try ... catch arm (especially catch _, _ -> or catch :throw, _ ->) around an effect intercepts that throw; letting the workflow keep executing would journal the next effect at a duplicate position and silently corrupt the run's history, so the next effect call — or the engine, on a normal return — raises this error instead.