spec 055: default PPM_OMP_CHUNK_TOKENS=0 (single-pass, matches 1850)

Earlier default 4194304 (OMP-chunked) was suboptimal — saves ~230s eval time
but loses ~0.010 BPB sidecar from chunk-reset penalty. PR openai#1850 chose single-
pass deliberately and pays the 252s scoring cost for the bigger gain.

Single-pass timing on 8H per 1850's measurements:
  pre-quant + gptq + ema:      ~85s
  diagnostic quantized eval:   ~60s
  non-overlap forward (8-way): ~20s
  file gather:                 ~5s
  single-pass PPM scoring:     ~250s  (CPU-bound, not GPU)
  ────────────────────────────────────
  total eval phase:            ~420s   under 600s cap

Smokes (where wallclock matters more than gain) can override with
PPM_OMP_CHUNK_TOKENS=4194304.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: leon2k2k2k

tmp_exec/launch_055_run.sh

@@ -79,7 +79,7 @@ export PPM_CONF_THRESHOLD=0.76          # tuned (vs 1850's 0.9)
 export PPM_NN_SKIP_THR_NATS=0.277       # = 0.40 bits, anti-hijack
 export PPM_LOG_CACHE_SIZE=1048576
 export PPM_OMP_THREADS=8
-export PPM_OMP_CHUNK_TOKENS=4194304     # OMP-chunked default
+export PPM_OMP_CHUNK_TOKENS="${PPM_OMP_CHUNK_TOKENS:-0}"     # default 0 = single-pass (best gain, ~250s on 8H); set 4194304 for OMP-chunked smoke
 
 # ── Per-run identity ──────────────────────────────────────────────────────
 export SEED="$SEED"