wip(assembler): round L30 -- FI floor ring defect fixed; transition cost recovered

The Gradient interface left native solid density in the air-side gap and snapped the face to
voxel levels (concentric ring steps on the FI floor). The owner Gradient path now writes signed
distance both sides; match error RMS 0.36 -> 0.11 m. Band and fade-tile culling cut transition
cost: whole view vs L24 SW +2.7%, FI +0.2%. Evaluator 16. Deterministic across compilers and
workers; interface and passage audits pass. Found: on the real FloatingIslands recipe, the
rock-column connected-ends audit fails (all styles); earlier matrices ran SurfaceWorld twice.

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

Standalone/Research/WorldAssemblerM3/Linux30/RunCrossing30.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python3
+"""Verify speed-only L30 hashes on the 24 m crossing against L29."""
+import re
+import subprocess
+import time
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[4]
+OUT = ROOT / "Saved/Linux/l30"
+OUT.mkdir(parents=True, exist_ok=True)
+BINARIES = {
+    "clang": ROOT / "Saved/Linux/l30/bin/VoxelForgeCoreHeadless-linux30-speed-fade",
+    "gcc": ROOT / "Saved/Linux/l30/bin/VoxelForgeCoreHeadless-linux30-speed-fade-gcc",
+}
+PATTERN = re.compile(r"^\[Pipeline(?:FullDetailHash|WholeViewHash|LODHash|ExactQueryHash)\].*$", re.M)
+passed = True
+for compiler, binary in BINARIES.items():
+    for recipe in ("surface-world", "floating-islands"):
+        reference_path = ROOT / f"Saved/Linux/linux29-final-crossing24-{compiler}-{recipe}.log"
+        reference = PATTERN.findall(reference_path.read_text(encoding="utf-8"))
+        for workers in (1, 8, 12):
+            name = f"crossing-speedonly-default-{compiler}-{recipe}-w{workers}"
+            logfile = OUT / f"{name}.log"
+            command = [
+                "prlimit", "--as=6442450944", "--", str(binary),
+                str(ROOT / "Standalone/data/owner_world.json"),
+                "--world-assembler-prototype", "--stream-benchmark", "--stream-pipeline",
+                "--stream-hash", "--force-generate", "--clip-radius=3",
+                "--max-clip-level=8", f"--workers={workers}",
+                "--camera-step=24,0,0",
+                "--region-crossing", f"--recipe={recipe}",
+            ]
+            started = time.monotonic()
+            with logfile.open("w", encoding="utf-8") as stream:
+                subprocess.run(command, stdout=stream, stderr=subprocess.STDOUT,
+                               check=True, timeout=1800)
+            elapsed = time.monotonic() - started
+            rows = PATTERN.findall(logfile.read_text(encoding="utf-8", errors="replace"))
+            ok = len(reference) == 12 and rows == reference
+            passed &= ok
+            print(f"{compiler} {recipe} W{workers} elapsed={elapsed:.3f}s "
+                  f"hash_rows={len(rows)} {'MATCH' if ok else 'MISMATCH'}", flush=True)
+print(f"[CrossingSpeedOnly] runs=12 status={'PASS' if passed else 'FAIL'}", flush=True)
+raise SystemExit(0 if passed else 1)