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>

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