core: A/A noise floor (±1%) and small hot-path trims for the cave planner (L137, output = v236)

Identical builds differ <=0.6% median; residual near-ready vs assembler/world is real: Surface World +2.9..+3.6%,
Vertical Shafts +4.0..+4.3%, Tunnel Network -3.6/+6.8%. Profile points at column-cache reads and the sweep lookup.
Removed an unused sample field and per-lookup shared_ptr refcounting. 16/16 seeds, fast tier, Clang/GCC green.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Standalone/Research/WorldAssemblerM3/Linux137/VerifyL137VersionOutput.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+"""Compare rendered Surface World hashes for v227 and the no-op v228 bump."""
+from __future__ import annotations
+
+import json
+import re
+import subprocess
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[4]
+OUT = ROOT / "Saved/Linux/l137/output-check"
+DATA = ROOT / "Standalone/data/owner_world.json"
+BINARIES = {
+    "v227": ROOT / "Saved/Linux/l137/bin/VoxelForgeCoreHeadless-l137-aa-a",
+    "v228": ROOT / "Saved/Linux/l137/bin/VoxelForgeCoreHeadless-l137-v228",
+}
+CAMERA = "8.000000000000,16.000000000000,-372.262695312500,0,0"
+HASHES = re.compile(
+    r"^\[Pipeline(?:FullDetailHash|WholeViewHash|MaterialHash|LODHash|ExactQueryHash)\].*$",
+    re.M)
+
+
+def run(version: str) -> tuple[list[str], str]:
+    OUT.mkdir(parents=True, exist_ok=True)
+    log = OUT / f"surface-world-{version}.log"
+    command = [
+        "taskset", "-c", "0-11", "prlimit", "--as=6442450944", "--",
+        "timeout", "1740s", str(BINARIES[version]), str(DATA),
+        "--world-assembler-prototype", "--stream-benchmark", "--stream-pipeline",
+        "--workers=8", "--clip-radius=3", "--max-clip-level=8", "--max-level=8",
+        f"--camera={CAMERA}", "--recipe=surface-world", "--stream-hash",
+        "--stream-scheduler-policy=3",
+    ]
+    with log.open("w", encoding="utf-8") as output:
+        result = subprocess.run(command, cwd=ROOT, stdout=output,
+                                stderr=subprocess.STDOUT, check=False, timeout=1740)
+    content = log.read_text(encoding="utf-8", errors="replace")
+    hashes = HASHES.findall(content)
+    if result.returncode or len(hashes) < 4:
+        raise SystemExit(f"hash run failed: {version}; exit={result.returncode}; log={log}")
+    return hashes, str(log.relative_to(ROOT))
+
+
+def main() -> int:
+    rows = []
+    for version in BINARIES:
+        hashes, log = run(version)
+        rows.append({"version": version, "hashes": hashes, "log": log})
+    match = rows[0]["hashes"] == rows[1]["hashes"]
+    summary = {"output_hashes_match": match, "rows": rows}
+    (OUT / "summary.json").write_text(json.dumps(summary, indent=2) + "\n")
+    print("[L137VersionOutput] " + json.dumps({
+        "output_hashes_match": match,
+        "hash_lines": len(rows[0]["hashes"]),
+        "v227": rows[0]["hashes"], "v228": rows[1]["hashes"]}, sort_keys=True))
+    return 0 if match else 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())