Complete upstream source is upstream-source.json (a JSON object mapping relative source paths to their exact text contents), commit a93510e4de59888f556effbae3152020500b6859. Restore each JSON entry at its relative path, install esbuild 0.28.2 as build-time tool, and run: esbuild src/api/Model.js --bundle --format=iife --global-name=Simulation --platform=browser --target=es2020 --outfile=engine.js. No minification. Browser runtime: serve this flat directory; index.html loads engine.js and game.js. All original game code is directly editable; no build required for game.js or CSS. AGPL-3.0-or-later, no warranty.