Jev Pendulum

Jev Pendulum rig design

Jev Pendulum simulates a rod hinged on a cart: Jev (TypeSafe's System One model) reads the rod's angle and swing every tick and picks a push on the cart to keep it up. The agent shapes pendulum.json — the rig (gravity, rod length, push authority, gusts) and the style line Jev balances by.

The loop

1. Update pendulum.json (title, gravity, maxTorque, gustEvery/gustStrength, and a style line that tells Jev a strategy). The viewer watches it and Jev adapts live — no restart, no second server.
2. node "$JEV_DSH/toolchain/check.mjs" verifies the workspace's pendulum.json is valid. Run it before you call a rig done.
3. Watch the rod. Does it stand, wobble, and sometimes drop on a hard rig — or always stand like a statue (too easy) or always fall (too hard)? That observation is the finding.

Reading the rig

The viewer shows the cart and rod, five force arrows on the cart sized by the probability of each push, the "no return" lines where gravity beats the hardest shove, a lean budget meter, a run timer against the best run, and a tilt trace with every gust marked. Good rigs produce drama: a gust throws the rod toward the no return line, Jev's "under control?" answer dips, it recovers — and at high gravity it drops. gravity is the difficulty dial: 4–5 never falls, 7 is tense, 10+ topples every few seconds. A shorter length is harder too. gustStrength and gustEvery push it toward the edge without tipping it by themselves.

Verifying a rig

node "$JEV_DSH/toolchain/check.mjs" returns non-zero when pendulum.json is invalid (no title, or a value outside its range, for example gravity 0.5..30, length 0.2..3, stepMs 30..2000). It also prints the lean past which the rod cannot be saved. It does not replace watching the motion: confirm Jev holds a mid gravity steady, that raising gravity or gusts makes it visibly struggle and fall, and that the style line shifts how decisively it recovers.

Driving Jev yourself

toolchain/jev.mjs exports a small client. Example (from the workspace) — ask Jev's read on a state before you commit to a rig:

node --input-type=module -e '
import { evaluate, jev } from "$JEV_DSH/toolchain/jev.mjs";
const res = await evaluate({
  state: "Keep the rod upright.\nA stiff rod of length 1.00 stands hinged on a cart. You push the cart left or right along a rail.\nangle: +8.0°  velocity: +0.30 rad/s   (positive = leaning right, it falls at ±60°)\ncart: velocity +0.00 m/s   rail drag 0.2 per s\ngravity: 7.0   damping: 0.50\npush: LEFT_HARD -1.60, LEFT -0.80, CENTER +0.00, RIGHT +0.80, RIGHT_HARD +1.60 m/s²",
  questions: {
    action: jev.choice(["LEFT_HARD", "LEFT", "CENTER", "RIGHT", "RIGHT_HARD"], "Which push steadies the rod right now?"),
  },
});
console.log(JSON.stringify(res.answers, null, 2));
'

Without TYPESAFE_API_KEY this uses the deterministic mock; set the key to hit live Jev.