Runnin' Mules! real-time multiplayer racing arcade

Role creator · Where: personal (cege7480/sigma-derby) · Built: April–July 2026 Stack: Three.js + React Three Fiber · Rapier physics · Socket.IO · React 18 + TypeScript · Node/Express · Firestore · Google Cloud Run

A real-time multiplayer digital horse-racing arcade: five horses, ten quinella bets, continuous race cycles. The Socket.IO server is authoritative on outcomes and payouts; clients are pure renderers, and a session can reconnect mid-race and slot back in without losing balance or wagers.

It is also the project that proves a point the other three can't: a solo developer with AI can now ship a full product across disciplines they don't personally practice: 3D art, rigged animation, voice acting, sound design.

How it was built, the AI angle

This is generative AI in the product, not just assistive AI in the editor.

Discipline	Normally needs	Here
3D horse models	a character artist	Meshy AI-generated GLBs, one per horse, each rigged with `Walk`/`Trot`/`Gallop`/`Rest`
Broadcast announcer	a voice actor + booth	Google Chirp 3 HD (`en-US-Chirp3-HD-Charon`), the whole phrase library rendered to MP3 on boot and cached in GCS
Splash / tutorial art	an illustrator	generated stills, reused as the four-step first-time-player walkthrough so the tutorial reads native to the brand
Jockey rig	a technical animator	a v3 rig with a proper racing seat, plus a 13-joint procedural fallback horse with velocity-driven crossfade

Measured 511 commits across all branches over ~12 weeks, 360 of them (70%) AI-attributed, mostly Claude co-authorship, plus 20 authored outright by copilot-swe-agent and anthropic-code-agent. A further 139 commits come from semantic-release, which automates versioning and changelog; those are release plumbing, not AI, and aren't counted.

The hand-built parts are the ones you'd expect to be hand-built: the authoritative race simulation, the payout math, the reconnection protocol, and the security model.

The screens

The stadium

Runnin' Mules stadium overview: grandstands, mowed infield, tote board, and the full oval track

Procedural grandstands, pine-tree perimeter, lamp posts, scoreboards, and a stadium-shaped infield, with procedural mowed turf and rake-lined dirt. Alfa Slab One for display headings; JetBrains Mono for every live numeral: odds, balance, timer.

Board + phone: the whole loop

_{Board / kiosk: a full-screen attract overlay with the station code and QR. Phones scan it (or type the 4-character code) to pair.}	_{Racing: the QR fades out and the race-cam follows the field around the oval with a TV broadcast HUD.}
_{Results: winning quinella and payout summary, then straight into the next cycle.}	_{Phone: quinella picker with all ten pairings and odds (left), and the jockey rhythm minigame that modulates your horse's speed (right).}

The parts I'm proudest of

A reusable camera cutscene system. Every shot is just a { position, lookAt, duration } function, so a new cutscene is a new array. Ships with the race-start gate cut, the pre-race paddock walk (one cameo per horse, spotlight card reveals the jockey bio), and a photo-finish inspector.
A ragdoll jockey. Rare chance per race a horse stumbles; the jockey detaches into a six-body ragdoll with spherical joints and gets launched into the grandstand. There is also a gameplay-triggered teeth-throw cutscene that fires when one rider's tap-rhythm crosses 85% while a rival's drops below 30%: cartoon overlay on every client, in-engine ragdoll on the board.
Real observability for a toy. Custom metrics to Google Cloud Monitoring every 60s, visualized in Grafana: request rate and latency, race throughput, betting economy, tap-rhythm distribution, auth rejections by reason, HTTP 4xx/5xx, Firestore errors, and client-side errors via a window.onerror beacon.
Security taken seriously anyway. The /hardware Socket.IO namespace requires a shared secret with constant-time compare (previously anyone could connect and spoof position events to alter race outcomes). Secrets live in Secret Manager and mount natively. Per-user rate limits on bets, taps, markers, and reactions. An aggregate marker cap so a careless admin can't inflate one player's balance indefinitely.
The iOS bug nobody warns you about. Mobile socket heartbeat-on-resume catches Safari's half-open WebSocket failure mode, socket.connected === true while every emit drops on the floor.

Why it matters

Everything else in this portfolio is enterprise plumbing. This one is the counter-example: the same AI-assisted method, pointed at a domain with no requirements document and no stakeholders, still produced a deployed, monitored, security-reviewed, continuously-released product, with 3D art and a broadcast voice a solo developer could not have made five years ago at any price.

Also, the jockeys throw their teeth. That part was not AI's idea.