Admin eb0b7de06e box3d: broad-phase hybrid — drop the parallel batch, keep the serial BVTT ...

The parallel batch machinery from be21d627a only ever existed to chase a
default-on multi-threaded win that never came (washer w8 still +54% with
the hybrid on). At w1 — the only configuration this opt-in flag is for —
parallel_for runs inline, so the serial path gives the identical result
for ~340 fewer lines. Wire up the previously-dead
dynamic_tree_self_pairs/cross_pairs into a serial collect_batch_candidates
(three BVTT self/cross traversals -> canonical (a,b,child) sort -> serial
filter into move_results[0]) and delete BatchWork, BatchCtx, batch_drain_*,
BatchFilterCtx, batch_filter_*, bvtt_step, dynamic_tree_bvtt_drain/expand,
and the batch_frontier/worker_* scratch fields.

Determinism preserved exactly: OFF 0x61E35C31/step314 bit-identical, ON
0xBE99C5F7/step313 identical across workers 1/2/4. The debug SET-equality
oracle and the determinism_broad_phase_hybrid_across_worker_counts test
are unchanged and still pass; zero warnings.

PGO: pgo.sh never trained -bp=1, so an off-path-only profile laid the
hybrid branch out cold and collapsed the win to ~-5%. Add one -b=8 -bp=1
training run (neutral for the default path — counts merge, the OFF branch
stays hot) and retrain.

Corrected README numbers to measured values (hybrid-trained profile,
paired -bp toggle, washer w1): pair-finding stage 7.6k -> 3.6k ms/1000
(-52%); total ~-17% (~19.0k vs ~22.6k), which beats C (20661) and narrows
Rapier's lead from ~23% to ~12% — not the "17.7k / within 5% / -19%"
be21d627a claimed. Still default-off (w8 regresses ~+54%), opt-in
single-threaded accelerator for churn-heavy scenes.

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

2026-07-06 10:08:45 +02:00

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