The constant [Engine.GuiInteraction] can be used to determine whether a workflow was run in the Designer or Gallery. Currently, there's no method to also find out whether a workflow was initiated by a schedule or run manually in the Gallery. The information is available in the Gallery but not forwarded to inside the workflow.
Please introduce a new variable [Engine.ScheduledRun] (or similar) which determines whether the workflow was initiated by a schedule (value "true" if boolean or "schedule" if string type) or manually (value "false" or "manual").