The Three-State Port Is One Endpoint Stratum Plus a Two-Sheet Through Cover
The six unsigned legal generator permutations form three orbits under exact endpoint reversal. Two orbits repeat an endpoint generator; one repeats the unique through-going generator. The endpoint-versus-through classification is therefore already a coarse type map, merging the two endpoint orbits.
The relative endpoint-polarity character is defined only on the through-going stratum and takes both signs. Hence the response port is constructed as one collapsed endpoint state together with a two-sheet orientation cover over the through-going state. Its cardinality three is stratified, not a homogeneous three-fold symmetry.
This explains why polarity affects only the exceptional generator while also preserving the earlier boundary: the construction is source-lawful, whereas its minimal sufficiency is certified by the distinct response profiles.
Evidence:
research/strominger/the-three-state-framing-port-is-response-minimal-not-universally-invariant.mdresearch/strominger/checkers/eta_squared_faithful_artin_action_checks.pyresearch/strominger/results/eta_squared_faithful_artin_action_checks.json
Verification: sixty-two of sixty-two exact gates pass.