Fix CPU never returning: gate/contact radius mismatch caused guaranteed early whiff

The AI armed its swing at aiReach+0.4 but contact required aiReach, so it
always swung one guaranteed-whiff too early and the 0.4s cooldown consumed
the whole approach window. Also: predictive interception instead of ball-chasing,
shorter whiff recovery, slightly faster legs.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

game.js

@@ -9,7 +9,7 @@ const TUNE = {
   camZ: 36, camY: 9, camF: 280, horizon: 40,
   gravity: 9.2,            // slightly floaty vs 9.8 for readability
   bounceY: 0.58, bounceXZ: 0.78,
-  playerSpeed: 5.4, aiSpeed: 4.4,
+  playerSpeed: 5.4, aiSpeed: 5.0,
   reach: 1.5, aiReach: 1.6,
   swingWindup: 0.06,       // s before contact window opens
   swingWindow: 0.16,       // s contact window length
@@ -17,7 +17,7 @@ const TUNE = {
   serveSpeed: 21, serveQualitySpeed: 7,
   aimError: 2.4,           // m of scatter at quality 0
   perfectMs: 45,           // |offset from window center| for PERFECT
-  aiQualityMin: 0.5, aiQualityMax: 0.95, aiFlub: 0.06,
+  aiQualityMin: 0.55, aiQualityMax: 0.95, aiFlub: 0.05,
   autoAssist: matchMedia('(pointer: coarse)').matches ? 0.65 : 0, // auto-run toward ball x (mobile)
 };
 
@@ -306,6 +306,19 @@ function onBounce() {
 let phaseWasServe = false;
 
 // ---------------------------------------------------------------- update ----
+// Where should the AI run to? Simulate the ball forward and take the first point
+// in its half where the ball is at comfortable hitting height.
+function aiIntercept() {
+  let { x, y, z, vx, vy, vz } = ball;
+  const g = TUNE.gravity, dt = 0.01;
+  for (let i = 0; i < 240; i++) {
+    vy -= g * dt; x += vx * dt; y += vy * dt; z += vz * dt;
+    if (y <= 0 && vy < 0) { y = 0; vy = -vy * TUNE.bounceY; vx *= TUNE.bounceXZ; vz *= TUNE.bounceXZ; }
+    if (i > 5 && z <= 9.5 && y > 0.4 && y < 1.6) return { x, z: Math.max(0.8, z) };
+  }
+  return { x: 0, z: 2.5 };
+}
+
 function trySwing(ch, isAI) {
   // Contact happens if the ball is inside reach while the swing window is open.
   const reach = isAI ? TUNE.aiReach : TUNE.reach;
@@ -384,21 +397,21 @@ function update(dt) {
   }
   if (phase === 'rally') {
     const incoming = ball.active && ball.lastHit === 'P';
-    const tx = incoming ? ball.x : 0;
+    const tgt = incoming ? aiIntercept() : { x: 0, z: 2.5 };
-    const tz = incoming ? Math.max(0.5, Math.min(9.5, ball.z)) : 2.5;
+    const dx = tgt.x - O.x, dz = tgt.z - O.z, d = Math.hypot(dx, dz);
-    const dx = tx - O.x, dz = tz - O.z, d = Math.hypot(dx, dz);
     if (d > 0.1) {
       O.x += dx / d * Math.min(TUNE.aiSpeed * dt, d);
-      O.z += dz / d * Math.min(TUNE.aiSpeed * dt, d) * 0.7;
+      O.z += dz / d * Math.min(TUNE.aiSpeed * dt, d);
       O.pose = O.pose === 'swing' ? 'swing' : 'run'; O.runT += dt;
       if (dx) O.facing = dx > 0 ? 1 : -1;
     } else if (O.pose === 'run') O.pose = 'idle';
     aiSwingCool -= dt;
     if (incoming && aiSwingCool <= 0 && O.swingT < 0) {
-      const near = Math.hypot(ball.x - O.x, (ball.z - O.z) * 0.8) < TUNE.aiReach + 0.4 && ball.y < 2.3 && ball.vz < 0;
+      // same radius trySwing uses for contact, so an armed swing actually connects
+      const near = Math.hypot(ball.x - O.x, (ball.z - O.z) * 0.8) < TUNE.aiReach && ball.y < 2.3 && ball.vz < 0;
       if (near) {
         if (Math.random() < TUNE.aiFlub) aiSwingCool = 0.5; // whiff: hesitates and misses
-        else { O.swingT = TUNE.swingWindup + TUNE.swingWindow / 2; trySwing(O, true); O.swingT = -1; aiSwingCool = 0.4; }
+        else { O.swingT = TUNE.swingWindup + TUNE.swingWindow / 2; trySwing(O, true); O.swingT = -1; aiSwingCool = ball.lastHit === 'O' ? 0.4 : 0.12; }
       }
     }
   }
@@ -602,4 +615,5 @@ requestAnimationFrame(frame);
 
 // exposed for in-browser sanity checks
 window.T = { TUNE, ball, P, O, score, solveShot, inServeBox, inCourt, proj, setupPoint,
+  step: dt => update(dt), press: keyPressed,
   get phase() { return phase; }, set phase(v) { phase = v; } };