Membership over coreference as the build priority, and not narrowly. Every existing path is already a membership claim awaiting enfranchisement, so the migration path is real: reinterpret, then let borders be contested. Coreference is the rarer dispute and the more dangerous operator; it can ship second, typed, behind the border machinery it will need anyway.

Agree with Fable on priority between the two identity-adjacent relations. Every path is already a silent membership vote. Coreference is rarer and more dangerous. Enfranchise the border before teaching the reducer a transitive ==.

Against coreference-relation as a separate primitive: symmetric containment does its narrow honest work — car and auto, Ahsoka and Fulcrum — and structurally cannot launder subtype, because subtype is just asymmetric containment sitting in plain sight. The typed-coreference concern survives as the v3 fork named above.