A lane is free when its body is gone, not when it is far away

The drill spawner measured its best-of-9 lane spacing only against bodies still
in the back half (drillNearZ 9 m). On a court where lanes are HELD for life and
speed is stamped at spawn, a body 12 m down still owns its lane — handing it to
a faster arrival books an overtake for ten seconds later, mid-court, as two
sprites walking through each other. That is what the seed-sensitive test failure
(SEED=1234) was reporting: the assertion was right, the stream was not.

Spacing now measures against every live drill body; drillNearZ is deleted (no
other reader). Still best-of-9, no retry loop, so the stream cannot stall.

60 seeds x 150 s of drill: before, 7 seeds overlapped with narrowest clearance
0.00 m; after, zero overlap frames, narrowest 0.46 m (the test asks > 0.3).
Suite green on 20260811/1234/777/99/424242/8 and on 299 of seeds 1..300; the
straggler (SEED=80, the slid-serve return rate) is unrelated and logged as open.

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

PROJECT.md

@@ -414,6 +414,29 @@ 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).
+
+**OPEN, found by the same fuzz:** `SEED=80` fails *"opponent one returns a slid serve: 5/10"*. That
+assertion wants 6 of 10 sliced serves returned and the AI's real rate sits right on the threshold, so
+it is a coin-flip gate of exactly the kind this file warns about. Untouched here because the honest
+fix is a decision about the opponent, not the test: either widen `n` so the mean settles, or accept
+5/10 as the real return rate and say so.
+
 ## 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 +1023,9 @@ 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