perf: build PAGE trace from dense memory store

[ColoCarletti]

What

Generate the PAGE trace tables by reading each cell's final (value, timestamp) straight from the dense per-page memory store, instead of first building a sparse FinalStateMap and doing one (mostly-miss) lookup per page offset.

Why

Those per-offset sparse-map lookups were the dominant cost of PAGE generation.
Reading the dense page slice directly is one indexed read per offset, no hashing.

Impact (ethrex 5-tx block, RTX 5090)

• PAGE table generation: 658ms → 260ms
• Trace generation: 2.63s → 2.25s (−15%)
• Total prove: 12.8s → 12.5s (−2.4%)

Produces the exact same PAGE trace — prove + verify pass.

Changes (3 files)

• prover/src/paged_mem.rs: add PagedMem::page_data() (dense per-page slice).
• prover/src/tables/page.rs: add generate_page_trace_from_dense().
• prover/src/tables/trace_builder.rs: generate_page_tables uses the dense path.

[ColoCarletti]

/bench 5

[ColoCarletti]

/bench-gpu

[github-actions]

GPU Benchmark (ABBA) — 44bcbf24f3 vs main (14 pairs)

_{RTX 5090 · Vast.ai datacenter @ $0.8423148148148147/hr · prover/cuda · drift-free A/B/B/A}

=== ABBA paired result  (improvement: - = PR faster) ===
  pairs: 14   mean A (PR): 17.797s   mean B (base): 18.178s

  [parametric] paired-t   mean -2.09%   sd 1.11%   se 0.30%
               95% CI: [-2.73%, -1.45%]   (t df=13 = 2.16)
  [robust]     median -2.21%   Wilcoxon W+=0 W-=105  p(exact)=0.0001  (z=-3.26)

  --- server stability (this run; compare across servers) ---
  run-to-run jitter:    A CV 0.67%   B CV 0.84%        (lower = steadier)
  within-session drift: +0.73% over the run, 1st->2nd half +0.25%
    (jitter -> Tier-1 cached gate floor; drift -> whether the cached baseline can be trusted)

  VERDICT: REAL IMPROVEMENT - PR faster by ~2.09% (t-CI and Wilcoxon agree)

  raw pairs: /tmp/abba_run/pairs.csv

_{- = PR faster. Trust the verdict when paired-t and Wilcoxon agree.}

[github-actions]

Benchmark — ethrex 20 transfers (median of 3)

_{Table parallelism: auto (cores / 3)}

Metric	main	PR	Δ
Peak heap	73028 MB	72504 MB	-524 MB (-0.7%) ⚪
Prove time	37.771s	37.531s	-0.240s (-0.6%) ⚪

✅ No significant change.

🔬 Looks like a small speedup (-0.6%) — below what 3 runs can confirm. Comment /bench-abba to run the drift-free ABBA tiebreaker (paired-t CI + exact Wilcoxon). Note: it occupies the bench server for ~30–40 min.
Optional pair count: /bench-abba 32 (20 resolves ~1%, 32 for ~0.6%).

✅ Low variance (time: 1.6%, heap: 0.6%)

_{Commit: 44bcbf2 · Baseline: cached · Runner: self-hosted bench}

[ColoCarletti]

/bench 10