FADE

You are at the brake-check pullout at 2,418 m with 38,000 kg behind you, seven kilometres of switchback grade below you, and a weigh station on the valley floor. The clock runs from the moment you roll until the moment you stand still on the scale — and if you slide past it, you are backing up while the clock keeps counting.

The twist: brakes are a fuel tank, not a control. Every stop you ask of the service brakes pours heat into the drums. They cool in the airstream, they fade as they cook — noticeably past 250°C, catastrophically past 600 — and at 700°C they catch fire. Drag the pedal from the summit and you will be out of brakes before halfway, at which point the mountain does the driving. The whole game is the real trucker's craft:

• Gear down before the grade bites. The box refuses any downshift that would over-rev the engine, so once you are too fast in too high a gear, that door is closed.
• Ride the jake. The engine brake (Space, three stages) is free retardation with zero heat — but it is only as strong as your revs, which means it is only as strong as your gear.
• Snub, never drag. Brake firmly to shed ten mph, then get all the way off the pedal and let the drums cool. Dragging them lightly the whole way down is how drums die.
• Two gravel runaway ramps will save your life, and cost you your time.

How to play: A/D or arrows steer, W throttle, S service brakes (hold — it ramps in), Space cycles the jake 0→1→2→3, Q/E shift, X reverse (for backing onto the scale), C camera, R restart. Full touch controls on mobile. Deliver the load intact and your descent time goes to the leaderboard (lower is better) against three dispatch times: bronze 11:00, silver 9:05, gold 7:46. Jackknife, rollover, a guardrail, or a brake fire ends it — each in its own way.

Under the hood: tractor and trailer are two rigid bodies joined at the fifth wheel by an impulse constraint, so jackknife and trailer swing come out of the hitch forces, not a script. Slip-based tires with combined grip and load sensitivity, real longitudinal weight transfer, a roll model that genuinely bifurcates at wheel lift (the trailer tips first, around 0.40 g), per-group drum thermodynamics with speed-dependent cooling, and an engine you can over-rev. Fixed 1/120 s physics step, decoupled from rendering. All audio is synthesized — the jake's staccato bark, brake squeal that rises with drum temperature, air hiss on release.

How it was made: this run's concept, tuning bar and words are one Claude model's; the simulation was implemented by another in a single self-contained HTML file, then tuned and torture-tested with headless bot drivers until the numbers closed — the dispatch times are set from actual bot descents, a naive pedal-dragging bot provably cooks its drums and jackknifes at 4.7 km, and the energy audit balances 158.9 MJ of dropped potential to within one percent.