Merge the drill lane fix and the rate-gate sample size into staging

index.html conflicted only on the cache-buster: staging was at 276 and the
branch at 275, so the merge takes 277 — a merge that reuses either number
leaves phones on the old build.

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

src/config.js

@@ -461,7 +461,6 @@ export const TUNE = {
   drillSeed: 4,     // bodies placed at the start so there is a queue to read from the first second
   drillSeedGap: 2.6,// m of depth between those seeded bodies
   drillSpawnZ: 0.6, // z they enter at (the far baseline is 0)
-  drillNearZ: 9.0,  // spawn spacing is measured against bodies nearer than this
   drillSpread: 3.4, // m either side of the centre line the lanes fan across
   drillSpeed: 0.85, // m/s at the bottom of the ramp (x the type's vMul)...
   drillSpeedMax: 2.0,// ...and at the top. Stamped per body AT SPAWN — constant v is also what lets

src/drill.js

@@ -73,15 +73,19 @@ function pickType() {
   return pool[Math.floor(Math.random() * pool.length)];
 }
 
-// ---- THE STREAM. One body at a time, spaced (best-of-9 lanes against the back half — a retry loop
+// ---- THE STREAM. One body at a time, spaced (best-of-9 lanes against EVERY live body — a retry loop
 // would stall the stream exactly when it should be getting harder), holding its lane all the way in.
+// The measure used to ignore anything past the back half, which was wrong for a court where lanes are
+// held for life and speeds are stamped per body: a lane 12 m down is still OWNED, and handing it to a
+// faster body just books the overtake for ten seconds later, where it lands as two sprites walking
+// through each other mid-court. A lane is free when its body is gone, not when it is far away.
 function spawnDrillBody(d) {
-  if (zombies.filter(z => z.drill).length >= TUNE.drillMaxOnCourt) return null;
-  const near = zombies.filter(z => z.drill && z.z < TUNE.drillNearZ);
+  const live = zombies.filter(z => z.drill);
+  if (live.length >= TUNE.drillMaxOnCourt) return null;
   let bx = 0, bs = -1;
   for (let k = 0; k < 9; k++) {
     const x = -TUNE.drillSpread + (2 * TUNE.drillSpread) * (k / 8) + (Math.random() - 0.5) * 0.5;
-    const s = near.length ? Math.min(...near.map(z => Math.abs(z.x - x))) : 1e9;
+    const s = live.length ? Math.min(...live.map(z => Math.abs(z.x - x))) : 1e9;
     if (s > bs) { bs = s; bx = x; }
   }
   const t = pickType();