Improved using hi-fi figure digitisation: sub-pixel container frame lines plus, for each domino, the darkness-profile centroids of its four edges fitted by TLS lines and intersected to recover the rectangle; then a settle-and-creep GPU optimiser (multi-chain settle at r near the target, warm-started micro-steps of r, exact rational acceptance at every step). Candidate side 7.951243483836697; exact rational verifier reproduces all 40 existing P90 scores.
P90 · Dominoes in a square · Discussion