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/RunL137Profile.py

@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+"""All-LOD inclusive L77 samples for assembler/world and L137 HEAD."""
+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/profile"
+DATA = ROOT / "Standalone/data/owner_world.json"
+BINARIES = {
+    "assembler-world": ROOT / "Saved/Linux/l137/profile-bin/VoxelForgeCoreHeadless-l137-profile-base",
+    "head": ROOT / "Saved/Linux/l137/profile-bin/VoxelForgeCoreHeadless-l137-profile-head",
+}
+STAMPS = {
+    "assembler-world": "4499fb2a8a4ede7d6cbc68d1b794f104658cdaae93ed9cacbc91fe7ff3fc3621",
+    "head": "dcf2ffa55fd6d62b3c7faf76229c3b99c635868dc1b694fc6e8f39e738775a4e",
+}
+CAMERA = "8.000000000000,16.000000000000,-372.262695312500,0,0"
+STAMP_RE = re.compile(r"^\[VoxelForgeSourceStamp\] sha256=([0-9a-f]+)$", re.M)
+SAMPLER_RE = re.compile(r"^\[L77Sampler\] action=stop (.*)$", re.M)
+SAMPLE_RE = re.compile(
+    r"^\[L77Sample\] pc=(0x\w+) lod=(\d+) stage=(\S+) route=(\S+) "
+    r"phase=(\S+) halo=(\d+) weight=(\d+)$", re.M)
+
+
+def run(version: str, replicate: int) -> dict:
+    OUT.mkdir(parents=True, exist_ok=True)
+    log = OUT / f"sw-{version}-r{replicate}.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}", "--profile-lod-work", "--stream-scheduler-policy=3",
+        "--linux77-profile",
+    ]
+    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, sampler = STAMP_RE.search(content), SAMPLER_RE.search(content)
+    samples = SAMPLE_RE.findall(content)
+    if (result.returncode or stamp is None or sampler is None
+            or stamp.group(1) != STAMPS[version] or "status=PASS" not in sampler.group(1)):
+        raise SystemExit(f"L77 profile failed or stamp mismatch: {log}; exit={result.returncode}")
+    sam = dict(re.findall(r"([a-zA-Z0-9_]+)=([^ ]+)", sampler.group(1)))
+    lods = sorted({int(row[1]) for row in samples})
+    row = {
+        "world": "Surface World", "version": version, "replicate": replicate,
+        "source_stamp": stamp.group(1), "workers": 8, "lods_sampled": lods,
+        "stored_samples": len(samples), "expanded_ticks": int(sam["expanded_ticks"]),
+        "lost": int(sam["lost"]), "timer_threads": int(sam["timer_threads"]),
+        "profiled_thread_cpu_s": float(sam["profiled_thread_cpu_s"]),
+        "handler_cpu_ms": float(sam["handler_cpu_ms"]),
+        "wall_s": round(time.monotonic() - started, 3),
+        "log": str(log.relative_to(ROOT)),
+    }
+    print("[L137ProfileRun] " + json.dumps(row, sort_keys=True), flush=True)
+    return row
+
+
+def main() -> int:
+    missing = [str(path) for path in [DATA, *BINARIES.values()] if not path.is_file()]
+    if missing:
+        raise SystemExit("missing L137 profile input: " + ", ".join(missing))
+    rows = []
+    for replicate, order in enumerate((
+            ("assembler-world", "head"), ("head", "assembler-world"),
+            ("assembler-world", "head")), 1):
+        for version in order:
+            rows.append(run(version, replicate))
+            (OUT / "runs-partial.json").write_text(
+                json.dumps(rows, indent=2) + "\n", encoding="utf-8")
+    (OUT / "runs.json").write_text(json.dumps(rows, indent=2) + "\n", encoding="utf-8")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())