Sector Parity Repairs the Entrance Gram but Opens a Wall Gate
One exact sector parity is algebraically sufficient to distinguish the two identically represented entrance doublets. With the up chain even and the down chain odd, it forbids the off-diagonal entrance kinetic Gram and wrong-sector Yukawa entrances while preserving all declared messenger vertices, vectorlike masses, and even cross-invariants supporting the noncollinear vacuum.
The parity equations have a unique solution after the common source assignments are frozen. This is a declared source-extension rigidifier, not a derived numerical selector. The nonzero odd down entrance vev spontaneously breaks the parity, so domain-wall history or an independently typed soft breaking becomes a new physical gate.
Evidence: research/flavor/flavor-entrance-sector-parity-repair.md and
research/flavor/results/wp629_entrance_sector_parity_repair.json.