wip(assembler): round L36 -- tunnel floor without washboard; FI mouth without shards (evaluator v23)

The walk tread was built per segment as a one-sided density clamp, so its crossing with the native
field moved at segment joins (L35: 2.25-2.48 cm washboard). Treads now overlap up to 2 m as bounded
signed-distance slabs (0.06 cm residual). The FI mouth's crater detail and tread met without a smooth
join; v23 filters the local field, drops thin isolated solids and smooth-unions the tread with the
terrain. New floor ripple and mouth fragment/crease audits with L35 as failing controls. 24/24
passage rows, 30/30 determinism, 16/16 invariants, LOD0-8 rings; cost within noise.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CSFYgsdW8ejZSyiMf4qRSX

Standalone/Research/WorldAssemblerM3/Linux36/RunCostL36.py

@@ -0,0 +1,88 @@
+#!/usr/bin/env python3
+"""Run five interleaved whole-view cost pairs against the L35 Clang binary."""
+import csv
+import math
+import re
+import statistics
+import subprocess
+import time
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[4]
+OUT = ROOT / "Saved/Linux/l36"
+BINARIES = {
+    "l35": ROOT / "Saved/Linux/l35/bin/VoxelForgeCoreHeadless-l35-final-clang",
+    "l36": OUT / "bin/VoxelForgeCoreHeadless-l36-final-clang",
+}
+ORDERS = (("l35", "l36"), ("l36", "l35"), ("l35", "l36"),
+          ("l36", "l35"), ("l35", "l36"))
+READY = re.compile(r"\bwhole_view_ready=([0-9.]+)s")
+rows = []
+failed = False
+
+
+for recipe in ("surface-world", "floating-islands"):
+    for pair, order in enumerate(ORDERS, 1):
+        for build in order:
+            name = f"cost-{recipe}-pair{pair}-{build}"
+            logfile = OUT / f"{name}.log"
+            command = [
+                "taskset", "-c", "0-11", "prlimit", "--as=6442450944", "--",
+                "timeout", "900s", str(BINARIES[build]),
+                str(ROOT / "Standalone/data/owner_world.json"),
+                "--workers=12", "--world-assembler-prototype", "--stream-benchmark",
+                "--stream-pipeline", "--force-generate", "--clip-radius=3",
+                "--max-clip-level=8", "--max-level=-1", f"--recipe={recipe}",
+            ]
+            started = time.monotonic()
+            try:
+                with logfile.open("w", encoding="utf-8") as stream:
+                    result = subprocess.run(command, cwd=ROOT, stdout=stream,
+                        stderr=subprocess.STDOUT, timeout=900, check=False)
+            except subprocess.TimeoutExpired:
+                result = None
+            elapsed = time.monotonic() - started
+            output = logfile.read_text(encoding="utf-8", errors="replace")
+            matches = READY.findall(output)
+            stamps = re.findall(
+                r"^\[WorldAssemblerRecipeAudit\] requested=([^ ]+) actual=([^ ]+).*status=([^ ]+)$",
+                output, re.M)
+            stamp_ok = stamps == [(recipe, recipe, "PASS")]
+            valid = (result is not None and result.returncode == 0 and len(matches) == 1
+                     and "hash=off" in output and "cache_hits=0" in output and stamp_ok)
+            ready = float(matches[0]) if len(matches) == 1 else math.nan
+            rows.append((recipe, pair, build, ready, elapsed,
+                         result.returncode if result else "TIMEOUT", valid))
+            failed |= not valid
+            print(f"[L36CostRun] recipe={recipe} pair={pair} build={build} "
+                  f"whole_view_ready={ready:.3f}s process_elapsed={elapsed:.1f}s "
+                  f"{'PASS' if valid else 'FAIL'} log={logfile}", flush=True)
+
+summary = OUT / "cost-runs.csv"
+with summary.open("w", newline="", encoding="utf-8") as stream:
+    writer = csv.writer(stream)
+    writer.writerow(("recipe", "pair", "build", "whole_view_ready_seconds",
+                     "process_elapsed_seconds", "exit_code", "status"))
+    writer.writerows((recipe, pair, build, f"{ready:.6f}", f"{elapsed:.3f}", code,
+                      "PASS" if valid else "FAIL")
+                     for recipe, pair, build, ready, elapsed, code, valid in rows)
+
+for recipe in ("surface-world", "floating-islands"):
+    by_build = {build: [row[3] for row in rows if row[0] == recipe and row[2] == build]
+                for build in BINARIES}
+    baseline = statistics.median(by_build["l35"])
+    current = statistics.median(by_build["l36"])
+    paired = []
+    for pair in range(1, 6):
+        values = {row[2]: row[3] for row in rows if row[0] == recipe and row[1] == pair}
+        paired.append((values["l36"] - values["l35"]) / values["l35"] * 100.0)
+    mad = statistics.median(abs(value - statistics.median(paired)) for value in paired)
+    print(f"[L36CostSummary] recipe={recipe} pairs=5 median_l35_s={baseline:.3f} "
+          f"median_l36_s={current:.3f} median_change_pct={(current/baseline-1)*100.0:+.2f} "
+          f"paired_change_pct={','.join(f'{value:+.2f}' for value in paired)} "
+          f"paired_mad_pct={mad:.2f}", flush=True)
+
+print(f"[L36Cost] runs={len(rows)} status={'FAIL' if failed else 'PASS'} summary={summary}",
+      flush=True)
+raise SystemExit(1 if failed or len(rows) != 20 else 0)