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/RunCost.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+"""Interleave five W12 hash-off whole-view cost triplets for L24/L29/L30."""
+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 = {
+    "l24": ROOT / "Saved/Linux/l24-source/bin/linux/VoxelForgeCoreHeadless-linux24-clang19",
+    "l29": ROOT / "Saved/Linux/bin/VoxelForgeCoreHeadless-linux29-clang",
+    "l30": ROOT / "Saved/Linux/l30/bin/VoxelForgeCoreHeadless-linux30-speed-fade",
+}
+ORDERS = (
+    ("l24", "l29", "l30"),
+    ("l29", "l30", "l24"),
+    ("l30", "l24", "l29"),
+    ("l24", "l30", "l29"),
+    ("l29", "l24", "l30"),
+)
+WHOLE_READY = re.compile(r"\bwhole_view_ready=([0-9.]+)s")
+rows = []
+for recipe in ("surface-world", "floating-islands"):
+    for pair, order in enumerate(ORDERS, 1):
+        for build in order:
+            name = f"cost-speedfade-{recipe}-pair{pair}-{build}"
+            logfile = OUT / f"{name}.log"
+            command = [
+                "prlimit", "--as=6442450944", "--", 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()
+            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
+            text = logfile.read_text(encoding="utf-8", errors="replace")
+            matches = WHOLE_READY.findall(text)
+            if len(matches) != 1 or "hash=off" not in text or "cache_hits=0" not in text:
+                raise SystemExit(f"invalid cost run: {name}; see {logfile}")
+            ready = float(matches[0])
+            rows.append((recipe, pair, build, ready, elapsed))
+            print(f"{recipe} pair={pair} build={build} whole_view_ready={ready:.3f}s "
+                  f"process_elapsed={elapsed:.3f}s", flush=True)
+
+summary = OUT / "cost-runs-speedfade.csv"
+summary.write_text("recipe,pair,build,whole_view_ready_seconds,process_elapsed_seconds\n" +
+    "".join(f"{recipe},{pair},{build},{ready:.6f},{elapsed:.6f}\n"
+            for recipe, pair, build, ready, elapsed in rows), encoding="utf-8")
+print(f"wrote {summary}", flush=True)