Ground-truth pass over the named flagship consumer (portfolio-optimiser's
'OKF-upload-inbox') found it does not exist as a seam: both optimiser siblings
are frozen at release, carry their own OKF layer, receive no external bundles,
and take no dependency on this guard. Defer consumer integration (stream 2)
until the guard is mature; mature it here first, Node-port-friendly. Next
concrete build is the in-repo OKF inbox showcase (mode-b import_bundle as a
receive/quarantine gate), spec'd under 'The OKF inbox showcase'.