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Pursue the paper's medial pigeonhole programme (R_T restriction relation, chain-pigeonhole conjecture) at the data level. Findings: R_T (outer<->inner boundary necklace, one Kempe-balanced colouring) is genuinely coupled, not a product of its projections. A uniform per-size boundary-state family threading every tile EXISTS at n=9 (unique per size, the balanced-block necklaces 0011/000011/012/00012 -- not monochromatic), but FAILS at n=12: size-7 seams admit no universal state (|D[7]|=0; near-universal 0001112 realised on 210/211 boundaries, blocked by one tile). So the uniform "same state everywhere" shortcut breaks once large odd seams appear and universals vanish as the tile population grows; the per-interface pigeonhole choice is genuinely needed. Pairwise gluability still holds, so this locates the conjecture's difficulty rather than obstructing gluing. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>