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>

PROJECT.md

@@ -414,6 +414,36 @@ zombie (now an occasional opponent, `TUNE.racketEvery`, not the every-game fixtu
   `RETURNED`, `DOUBLE KILL`) is a footnote to something you already watched happen. Sharing the loud
   FACE with the milestone cards is right; sharing their SIZE made every footnote read as a milestone.
 
+## Session log: a lane is free when its body is gone, not when it is far away (2026-08-16)
+
+A seed-sensitive red suite (`SEED=1234 node test.js` failed on the drill's "spaced *after the walk
+in*" assertion) turned out to be the assertion telling the truth: **two drill bodies genuinely walked
+through each other.** The spawner measured its best-of-9 lane spacing only against bodies with
+`z < drillNearZ` (9 m) — sound for a court where bodies wander, wrong for this one, where a lane is
+HELD for life and speed is stamped at spawn. A body 12 m down still owns its lane; handing that lane
+to a faster arrival does not create a spacing problem at spawn, it books an overtake for ten seconds
+later, mid-court, as two sprites occupying the same metre. The fix is the filter: spacing is measured
+against every live drill body, `drillNearZ` is deleted (it had no other reader). No retry loop, so
+the stream still cannot stall.
+
+Measured, 60 seeds × 150 s of drill each: before, **7 seeds produced overlaps, narrowest clearance
+0.00 m**; after, **zero overlap frames, narrowest 0.46 m** (the test asks for > 0.3). Peak on court
+is still the cap of 7, so the fan is wider, not thinner. Suite green on 20260811 / 1234 / 777 / 99 /
+424242 / 8, and on 299 of seeds 1..300 — the one straggler is unrelated and still open (see below).
+
+**The one straggler the same fuzz found, and the arithmetic to copy for any rate gate here.**
+`SEED=80` failed *"opponent one returns a slid serve: 5/10"*. The receiver is innocent: measured over
+200 trials a seed across eight seeds, the real return rate is **0.85..0.92**. The gate was simply too
+small a sample — asking 6 of 10 at p ≈ 0.88 fails with probability ~0.004, one seed in 230, and 300
+seeds duly produced one. **n is now 40 at the same 60% bar**, which puts the threshold five standard
+deviations below the true rate while still failing instantly if the receiver regresses toward the
+0-in-24 the test was born from. It costs nothing — a returned serve breaks the frame loop early, so
+the whole suite still runs in about a tenth of a second. Green on seeds 1..400.
+
+The general lesson: **a pass/fail gate on a random rate needs its sample size derived from the rate,
+not guessed.** If the true rate is p and the bar is b, n has to put b several standard deviations
+(`sqrt(p(1-p)/n)`) below p, or the gate is a slow coin flip that trains you to re-run the suite.
+
 ## Session log: THE NETPLAY LOBBY — a link to send, a code to type, a name to be (2026-08-15)
 
 Oliver: *"multiplayer should be easier to setup — a share with link next to the code; also entering
@@ -1000,9 +1030,9 @@ are the ones being called now, which is a better decoy than the old fixed-batch
 - **`PLACEMENTS` is deleted along with the marks.** Nothing rushes anywhere and nothing stops, so
   there are no shapes to place — the geometry now comes from lane choice at spawn plus the depth the
   stream naturally strings bodies out into. That is a net DELETION of the fanciest code in the file.
-- **Spacing is best-of-9 lane sampling** against everyone still in the back half, not a retry loop:
-  a hard minimum would silently stall the stream at exactly the moment it is meant to be getting
-  harder, which reads as the mode dying.
+- **Spacing is best-of-9 lane sampling** against every live drill body (it measured only the back
+  half until 2026-08-16, see that session log), not a retry loop: a hard minimum would silently stall
+  the stream at exactly the moment it is meant to be getting harder, which reads as the mode dying.
 - **A DRILL BODY HOLDS ITS LANE**, and this was the fix the screenshot forced. `updateZombies` homes
   bodies onto the player's x once they cross the net — a gore-mode behaviour — so they arrived nicely
   spread and then bunched into an unreadable knot right in front of you. Spawn spacing cannot survive

index.html

@@ -659,6 +659,6 @@ if (location.hostname !== 'splatter-tennis.wuwi.one') {
     </div>
   </div>
 </div>
-<script type="module" src="src/main.js?v=276"></script>
+<script type="module" src="src/main.js?v=277"></script>
 </body>
 </html>

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();

test.js

@@ -1108,8 +1108,14 @@ test('a served ball with a slide on it is no longer a free kill', () => {
     }
     return false;
   };
+  // n = 40, NOT 10, and this is the arithmetic to copy for any other rate gate here. The real return
+  // rate is ~0.88 (measured, 200 trials a seed across eight seeds: 0.85..0.92), so a 10-sample gate
+  // asking for 6 fails whenever the tail lands — p ~= 0.004, which is one seed in 230 and duly showed
+  // up as SEED=80. At 40 the same 60% bar sits five standard deviations below the true rate: the gate
+  // still fails instantly if the receiver regresses toward the 0-in-24 this test was born from, and
+  // it costs nothing (a returned serve breaks the frame loop early).
   let got = 0;
-  const n = 10;
+  const n = 40;
   for (let i = 0; i < n; i++) if (serve(-0.5)) got++;
   assert.ok(got >= n * 0.6, `opponent one returns a slid serve: ${got}/${n} (was 0)`);
 });