Messenger Vertices Reconstruct Both Standard Model Stages
The already declared source interactions uniquely transport each
right-handed-quark Standard Model representation through both vectorlike
messenger stages. Both up stages transform as (3,1,2/3) and both down stages
as (3,1,-1/3).
All six route vertices have zero hypercharge residual, and every vectorlike pair cancels its cubic, mixed, and gravitational anomalies. Gauge invariance forces the conjugate electroweak doublet at the up entrance. Using the plain doublet leaves residual one; assigning a down-type second up stage leaves residual minus one.
This closes one conservative WP626 registry gap without using fitted flavor coordinates. It does not select a numerical flavor point or supply a physical instrument.
Evidence: research/flavor/flavor-messenger-sm-representation-reconstruction.md
and research/flavor/results/wp627_messenger_sm_representation_reconstruction.json.