Jev Pong

Jev Pong court design

Jev Pong simulates a paddle-defense rally: Jev (TypeSafe's System One model) reads the ball's position and velocity every tick and moves the paddle to meet the return. Each hit speeds the ball up, so a long rally outruns the paddle. The agent shapes pong.json — the court, the paddle's authority, and the starting ball speed.

The loop

1. Update pong.json (title, courtW/courtH, speed, maxSpeed, accel, 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 pong.json is valid. Run it before you call a court done.
3. Watch the rally. Does Jev return a few balls, speed the ball up, and sometimes drop it — or never miss (too easy) / always drop (too hard)? That observation is the finding.

Reading the court

The viewer shows the court, five ghost paddles lit by the probability of each move, a ring where the ball will cross Jev's wall, the paddle's remaining reach, a pace meter with the pace where the paddle is outrun, the text Jev reads, and a bar for every finished rally. Good courts produce a natural arc: Jev holds a few returns, the ball accelerates, Jev scrambles harder, and it finally slips past. speed sets the serve pace; accel controls how fast each rally runs away; maxSpeed is how far a plain paddle move goes per decision (a FAST move goes twice as far).

Verifying a court

node "$JEV_DSH/toolchain/check.mjs" returns non-zero when pong.json is invalid (no title, or a value outside its range, for example speed 1..60 or stepMs 30..2000). It also prints the pace past which a far ball is out of the paddle's reach. It doesn't replace watching the motion: confirm Jev holds a low speed comfortably, that raising speed or accel shortens rallies and raises the miss count, and that the style line shifts how decisively it moves.

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 court:

node --input-type=module -e '
import { evaluate, jev } from "$JEV_DSH/toolchain/jev.mjs";
const res = await evaluate({
  state: "Keep the rally alive.\nYou are the paddle on the left wall of a 200x120 court. y 0 is the top, y grows downward.\npaddle: centre y 50.0, half-height 13.0, face at x 8\npaddle speed: a plain move shifts it 2.0 per decision, a FAST move 4.0 per decision\nball: x 40.0  y 70.0  vx -6.0  vy 2.0  radius 3  (toward you)\nspeed: 6.0 per decision   rally: 0",
  questions: {
    move: jev.choice(["MOVE_UP_FAST", "MOVE_UP", "HOLD", "MOVE_DOWN", "MOVE_DOWN_FAST"], "Which paddle move keeps the rally alive?"),
  },
});
console.log(JSON.stringify(res.answers, null, 2));
'

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