core: stamp passage route slabs into the tile cache (L125, evaluator v225)

Conservative route slabs with an outside sentinel, tight expanded segment bounds; DensityGrid exact fallbacks
479k -> 0 per run. Near-ready 2-14% faster than L119, still +4.7..+10.2% vs L109; whole view within -0.5..+8%.
Same look (floor offset 7.884 mm, captures checked), seam audit bit-identical, fast tier + walk audits,
Clang/GCC W1/W8/W12 determinism green. BVH and 25 cm tolerance trials rejected. Not for merge yet.

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

Standalone/Research/WorldAssemblerM3/Linux125/RunL125DensityProbe.py

@@ -0,0 +1,78 @@
+#!/usr/bin/env python3
+"""Probe reconstructed tunnel floor roots at the nine L119 stations."""
+from __future__ import annotations
+
+import csv
+import json
+import math
+import os
+import re
+import statistics
+import subprocess
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[4]
+OUT = ROOT / os.environ.get("L125_PROBE_DIR", "Saved/Linux/l125/density-probe")
+BINARY = ROOT / os.environ.get("L125_PROBE_BINARY",
+    "Saved/Linux/l125/bin/VoxelForgeCoreHeadless-l125-clang")
+DATA = ROOT / "Standalone/data/owner_world.json"
+SLOPE = re.compile(
+    r"^\[L115DensitySlopeSample\] passage=(\S+) station=(\S+) s_m=([\d.]+) "
+    r".*?planned_floor_m=(-?[\d.]+) root_floor_m=(-?[\d.]+|nan) "
+    r"residual_m=(-?[\d.]+|nan)", re.M)
+
+
+def main() -> int:
+    OUT.mkdir(parents=True, exist_ok=True)
+    log, layout = OUT / "owner4-clang.log", OUT / "layout.json"
+    command = [
+        "taskset", "-c", "0-11", "prlimit", "--as=6442450944", "--",
+        "timeout", "1740s", str(BINARY), str(DATA), "--world-assembler-prototype",
+        "--stream-benchmark", "--stream-pipeline", "--workers=12", "--clip-radius=3",
+        "--max-clip-level=8", "--max-level=8",
+        "--camera=8,16,-372.2626953125,0,0", "--audit-resolved-layout-passages",
+        f"--resolved-layout-output={layout}",
+    ]
+    with log.open("w", encoding="utf-8") as stream:
+        result = subprocess.run(command, cwd=ROOT,
+            env={**os.environ, "VOXELFORGE_L115_DENSITY_PROFILE": "1"},
+            stdout=stream, stderr=subprocess.STDOUT, check=False, timeout=1740)
+    if result.returncode:
+        raise SystemExit(f"density probe failed: {log}; exit={result.returncode}")
+    text = log.read_text(encoding="utf-8", errors="replace")
+    groups: dict[tuple[str, str], list[dict]] = {}
+    for passage, station, distance, planned, root, residual in SLOPE.findall(text):
+        root_value = float(root) if root != "nan" else math.nan
+        residual_value = float(residual) if residual != "nan" else math.nan
+        groups.setdefault((passage, station), []).append({
+            "route_s_m": float(distance), "planned_floor_m": float(planned),
+            "root_floor_m": root_value, "offset_m": residual_value})
+    summary = []
+    with (OUT / "zero-crossing-offsets.csv").open("w", newline="", encoding="utf-8") as stream:
+        writer = csv.DictWriter(stream, fieldnames=("passage", "station", "route_s_m",
+            "planned_floor_m", "root_floor_m", "offset_m"))
+        writer.writeheader()
+        for (passage, station), samples in sorted(groups.items()):
+            for sample in samples:
+                writer.writerow({"passage": passage, "station": station, **sample})
+            finite = [sample["offset_m"] for sample in samples
+                      if math.isfinite(sample["offset_m"])]
+            summary.append({"passage": passage, "station": station,
+                "samples": len(samples), "finite_roots": len(finite),
+                "max_abs_offset_m": max(map(abs, finite)) if finite else None,
+                "median_abs_offset_m": statistics.median(map(abs, finite))
+                    if finite else None,
+                "p95_abs_offset_m": sorted(map(abs, finite))[
+                    min(len(finite)-1, math.ceil(0.95*len(finite))-1)]
+                    if finite else None})
+    if not summary or any(item["samples"] != 51 for item in summary):
+        raise RuntimeError("density profile is missing 51-sample route stations")
+    (OUT / "zero-crossing-summary.json").write_text(
+        json.dumps(summary, indent=2) + "\n", encoding="utf-8")
+    print(f"[L125DensityProbe] exit={result.returncode} stations={len(summary)} "
+          f"log={log.relative_to(ROOT)}", flush=True)
+    return result.returncode
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())