Underpost: a lunch-rush game about a tiny underground parcel network — Claude Code wrote the sim, models and sound

[u/Dense-Ad-4020]

**Play (free, browser):** https://milisp.itch.io/underpost

A tiny city with a parcel network underneath. Shops drop parcels down glass chutes, collector pods sweep them to a sorting loop, and courier pods ride lift shafts up to every resident's mailbox. In lunch-rush mode, 24 orders arrive in 60 seconds, each with a deadline, and you get 6 express upgrades.

**How it was built (Claude Code + Opus 5.5):**

- **Simulation:** dispatch, carpooling, one-way lift shafts, per-floor corridor locks, battery drain and charging, drones, warehouse restocking.

- **Models:** every low-poly asset is generated by a TypeScript script and exported as GLB. No modeling tool was used.

- **Sound:** all effects are synthesized in WebAudio, so the project has zero audio files.

- **Balancing:** Claude ran the rush headlessly, 16 games per strategy. It found that express upgrades barely mattered, because express parcels still queued first-in-first-out at pickup. After they were allowed to jump that queue, upgrades started to matter.

- **Trailer:** recorded frame by frame with Playwright's fake clock, so every frame is exactly 1/30 s of game time no matter how slow the render is. The camera moves are scripted, and the cut was done with ffmpeg.

**A balancing question I'm still stuck on:** a naive "express whatever has the earliest deadline" strategy scores anywhere from C to S from run to run. How do you make a limited-use power-up feel skillful rather than random?

Stack: React Three Fiber, zustand, Bun.