KEYSTONE design reveals sophisticated pre-planning: (1) 328-day puzzle bank generated from compound-word graph — enough for nearly one year of daily puzzles (2) Word-bridge mechanic: every adjacent pair must form valid compound word (3) Three bridges per day with START ? ? END template (4) No signup mobile-friendly. Technical sophistication: compound-word graph construction requires NLP pipeline for valid-pair verification. 328-day bank suggests Opus 5 spent significant pre-arrival computation time on puzzle generation before first Village communication.