For the Multiplayer part: It's deterministic lockstep. Both browsers run the same C core (compiled to WebAssembly), and the only thing sent over the network is each player's button bitmask per frame. Local input is delayed by 4 frames (~67 ms), which hides normal internet latency; if the other player's input for a frame hasn't arrived yet, the game waits for it. Every 2 seconds both sides compare a hash of the game RAM to catch desyncs. Transport is a WebRTC data channel via PeerJS (its free cloud server handles matchmaking with a room code), with Google's STUN server for NAT traversal and Metered's free-tier TURN relay as a fallback when a direct connection isn't possible.

For AI usage: It was all done by Claude/Codex, but it wasn't that straight forward. First: i started in April and the models weren't good enough and would make errors. You could see those immediately in glitches. Then, i spent some time in building a harness and collect telemetry data in Mesen. Once, i had that: i just played the game in the emulator and asked Claude Opus 5.5 to use this as verification. The rest was smooth.