Prompt
Rebuild "Chess: Machine Thoughts" as a separate, playable browser game using JavaScript, HTML, SVG, Web Worker, Browser. Preserve the observed gameplay: A complete chess engine with legal moves, perft-tested rules, candidate move evaluation and principal-variation ghost pieces. Support human-vs-engine sides, self-play, time controls, undo, board flip and new games. Use Claude Opus 5.5 only as the documented creator attribution; some games call DeepSeek at runtime, which is separate from the build-model claim. Use a scripted/demo fallback when the optional model or network is unavailable. Implement the source-observed start state, controls, rules, game-state transitions, progression and completion/failure feedback. Keep it self-contained and verify the behavior against https://github.com/swan4er/opus-100-projects/blob/main/002-chess-mind/README.md and https://github.com/swan4er/opus-100-projects/blob/main/002-chess-mind/index.html.