wip(assembler): round L31 -- FI recipe column audit corrected; recipe-stamped audit runner

On the real FloatingIslands recipe, column caps sit inside anchor-island rock and native bedrock;
the old check sampled the route foot. The audit now samples each planned cap against the native
field (negative control: a cap moved into air is detected). The audit runner records requested vs
actual recipe and exits on mismatch. All 16 passage rows (4 styles x 2 recipes x 2 compilers) pass.
The readable shader uses a smooth tint. Interim: FI Gradient displacement capped at width/256
(flat floor, no contour rings); restoring real undulation is L32. Evaluator 19.

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

Standalone/Research/WorldAssemblerM3/Linux31/RunCostL31.py

@@ -0,0 +1,103 @@
+#!/usr/bin/env python3
+"""Run five interleaved W12 whole-view pairs against the final L30 binary."""
+import re
+import statistics
+import subprocess
+import time
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[4]
+OUT = ROOT / "Saved/Linux/l31"
+OUT.mkdir(parents=True, exist_ok=True)
+BINARIES = {
+    "l30": ROOT / "Saved/Linux/l30/bin/VoxelForgeCoreHeadless-linux30-speed-fade",
+    "l31": OUT / "bin/VoxelForgeCoreHeadless-linux31-clang",
+}
+ORDERS = (("l30", "l31"), ("l31", "l30"), ("l30", "l31"),
+          ("l31", "l30"), ("l30", "l31"))
+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 = [
+                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, stdout=stream, stderr=subprocess.STDOUT,
+                                            timeout=1800, check=False)
+            except subprocess.TimeoutExpired:
+                result = None
+            elapsed = time.monotonic() - started
+            text = logfile.read_text(encoding="utf-8", errors="replace")
+            matches = READY.findall(text)
+            if build == "l31":
+                stamps = re.findall(
+                    r"^\[WorldAssemblerRecipeAudit\] requested=([^ ]+) actual=([^ ]+).*status=([^ ]+)$",
+                    text, re.M)
+                actual_recipe = stamps[0][1] if len(stamps) == 1 else "missing"
+                stamp_ok = stamps == [(recipe, recipe, "PASS")]
+            else:
+                configured = re.findall(
+                    r"^\[HeadlessConfig\].*\brecipe=([^\s]+)", text, re.M)
+                actual_recipe = configured[0] if len(configured) == 1 else "missing"
+                floating_plan = "[FloatingIslandWorldAssembly]" in text
+                surface_plan = "[WorldAssemblerPrototype]" in text
+                plan_matches = ((actual_recipe == "floating-islands" and floating_plan)
+                                or (actual_recipe == "surface-world" and not floating_plan
+                                    and surface_plan))
+                marker = (f"[L31BaselineRecipeAudit] requested={recipe} actual={actual_recipe} "
+                          f"headless_recipe={configured[0] if len(configured) == 1 else 'missing'} "
+                          f"floating_island_plan={'present' if floating_plan else 'absent'} "
+                          f"surface_world_plan={'present' if surface_plan else 'absent'} "
+                          f"status={'PASS' if actual_recipe == recipe and plan_matches else 'FAIL'}\n")
+                with logfile.open("a", encoding="utf-8") as stream:
+                    stream.write(marker)
+                text += marker
+                stamp_ok = (actual_recipe == recipe and plan_matches
+                            and len(configured) == 1)
+            valid = (result is not None and result.returncode == 0 and len(matches) == 1
+                     and "hash=off" in text and "cache_hits=0" in text)
+            if build == "l31":
+                valid = valid and stamp_ok and actual_recipe == recipe
+            else:
+                valid = valid and stamp_ok and "status=PASS" in marker
+            ready = float(matches[0]) if len(matches) == 1 else float("nan")
+            rows.append((recipe, pair, build, ready, elapsed,
+                         result.returncode if result else "TIMEOUT", valid))
+            print(f"{recipe} pair={pair} build={build} whole_view_ready={ready:.3f}s "
+                  f"process_elapsed={elapsed:.1f}s {'PASS' if valid else 'FAIL'}", flush=True)
+            failed |= not valid
+
+summary = OUT / "cost-runs.csv"
+summary.write_text(
+    "recipe,pair,build,whole_view_ready_seconds,process_elapsed_seconds,exit_code,status\n" +
+    "".join(f"{recipe},{pair},{build},{ready:.6f},{elapsed:.3f},{code},"
+            f"{'PASS' if ok else 'FAIL'}\n"
+            for recipe, pair, build, ready, elapsed, code, ok in rows), encoding="utf-8")
+
+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}
+    l30 = statistics.median(by_build["l30"])
+    l31 = statistics.median(by_build["l31"])
+    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["l31"] - values["l30"]) / values["l30"] * 100.0)
+    print(f"[L31CostSummary] recipe={recipe} pairs=5 median_l30_s={l30:.3f} "
+          f"median_l31_s={l31:.3f} median_change_pct={(l31/l30-1)*100.0:+.2f} "
+          f"paired_change_pct={','.join(f'{value:+.2f}' for value in paired)}", flush=True)
+
+print(f"[L31Cost] runs={len(rows)} status={'FAIL' if failed else 'PASS'} summary={summary}", flush=True)
+raise SystemExit(1 if failed or len(rows) != 20 else 0)