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/RunL137Determinism.py

@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+"""Compare L137 Clang/GCC composed hashes at W1, W8, and W12."""
+from __future__ import annotations
+
+import json
+import re
+import subprocess
+import time
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[4]
+OUT = ROOT / "Saved/Linux/l137/determinism"
+DATA = ROOT / "Standalone/data/regression/owner_world_2strate_l61.json"
+BINARIES = {
+    "clang": ROOT / "Saved/Linux/l137/fast/bin/VoxelForgeCoreHeadless-fast-clang",
+    "gcc": ROOT / "Saved/Linux/l137/fast/bin/VoxelForgeCoreHeadless-fast-gcc",
+}
+STAMP = "dcf2ffa55fd6d62b3c7faf76229c3b99c635868dc1b694fc6e8f39e738775a4e"
+CAMERA = "-4.688214,38.662384,-505.781342,-28.446,0"
+HASH_RE = re.compile(
+    r"^\[Pipeline(?:FullDetailHash|WholeViewHash|MaterialHash|LODHash|ExactQueryHash)\].*$",
+    re.M)
+STAMP_RE = re.compile(r"^\[VoxelForgeSourceStamp\] sha256=([0-9a-f]+)$", re.M)
+
+
+def main() -> int:
+    if any(not path.is_file() for path in (DATA, *BINARIES.values())):
+        raise SystemExit("missing L137 determinism binary or owner fixture")
+    OUT.mkdir(parents=True, exist_ok=True)
+    rows = []
+    baseline: tuple[str, ...] | None = None
+    for compiler, binary in BINARIES.items():
+        for workers in (1, 8, 12):
+            label = f"determinism-{compiler}-w{workers}"
+            log = OUT / f"{label}.log"
+            command = ["taskset", "-c", "0-11", "prlimit", "--as=6442450944", "--",
+                "timeout", "1740s", str(binary), str(DATA),
+                "--world-assembler-prototype", "--stream-benchmark", "--stream-pipeline",
+                f"--workers={workers}", "--clip-radius=3", "--max-clip-level=0",
+                "--max-level=0", f"--camera={CAMERA}", "--stream-hash-tiles",
+                "--force-generate", "--recipe=surface-world", "--render-distance-chunks=0",
+                "--landmark-chamber-demo", "--ore-veins-demo"]
+            started = time.monotonic()
+            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")
+            stamp = STAMP_RE.search(content)
+            hashes = tuple(HASH_RE.findall(content))
+            passed = (result.returncode == 0 and stamp is not None
+                      and stamp.group(1) == STAMP and len(hashes) >= 4)
+            if baseline is None and passed:
+                baseline = hashes
+            elif baseline is not None:
+                passed &= hashes == baseline
+            row = {"compiler": compiler, "workers": workers, "exit": result.returncode,
+                   "stamp": stamp.group(1) if stamp else None, "hash_lines": len(hashes),
+                   "hashes_match_first": hashes == baseline, "passed": bool(passed),
+                   "elapsed_s": round(time.monotonic() - started, 3),
+                   "log": str(log.relative_to(ROOT))}
+            rows.append(row)
+            print("[L137DeterminismRun] " + json.dumps(row, sort_keys=True), flush=True)
+            if not passed:
+                (OUT / "summary.json").write_text(json.dumps(
+                    {"status": "FAIL", "stamp": STAMP, "runs": rows}, indent=2) + "\n")
+                raise SystemExit(f"determinism mismatch; see {log}")
+    (OUT / "summary.json").write_text(json.dumps(
+        {"status": "PASS", "stamp": STAMP, "runs": rows}, indent=2) + "\n")
+    print(f"[L137DeterminismSummary] runs={len(rows)} stamp={STAMP} status=PASS")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())