Constant STREAM_EXEC_GATE 

pub const STREAM_EXEC_GATE: StructuralGate;

A stream source in a namespace that has not opted in to STREAM_EXEC_ANNOTATION. Shares MoverPermitted with PRIVILEGED_MOVER_GATE — both answer “may this mover run here at all?” — but carries its own reason, because the fix is a different annotation and conflating them would send an admin to the wrong one.