AGENTS.md

This is NOT the Next.js you know

This version has breaking changes — APIs, conventions, and file structure may all differ from your training data. Read the relevant guide in node_modules/next/dist/docs/ before writing any code. Heed deprecation notices.

Multiplayer relay

server/ is a separate Node package (the WebSocket presence relay), NOT part of the Next build. It has its own package.json/Dockerfile and deploys as its own service. The Next app talks to it over NEXT_PUBLIC_WS_URL (inlined at build). Run both locally with npm run dev:all. Positions cross the wire as absolute BigInt hex coords (decimal strings) + intra-hex offset; the receiver re-localises against its floating origin every frame. The BigInt magnitude guard must precede any Number() on a coord delta — see memory/multiplayer.md.

Roster / presence: a peer must be registered the moment it joins, not on its first state — otherwise a motionless reader is invisible to everyone already connected. The relay welcome includes coord-less peers (...(p.last||{})) and join carries name; the client registers on join and pushSample skips the sample (but still registers the peer) when tq/tr are null — BigInt(undefined) would throw and abort the whole welcome, dropping every peer after it. The roster UI reads the reactive useRoster() snapshot (rebuilt in emit()).