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/CompareDeterminismL31.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+"""Compare L25 and 24 m crossing hash records for matching recipe/compiler/workers."""
+import re
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[4]
+OUT = ROOT / "Saved/Linux/l31"
+pattern = re.compile(r"^\[Pipeline(?:FullDetailHash|WholeViewHash|LODHash|ExactQueryHash)\].*$", re.M)
+lines = []
+failed = False
+for recipe in ("surface-world", "floating-islands"):
+    for compiler in ("clang", "gcc"):
+        for workers in (1, 8, 12):
+            left = pattern.findall((OUT / f"l25-{compiler}-{recipe}-w{workers}.log").read_text())
+            right = pattern.findall((OUT / f"crossing24-{compiler}-{recipe}-w{workers}.log").read_text())
+            same = bool(left) and len(left) == 12 and left == right
+            failed |= not same
+            lines.append(f"{recipe},{compiler},W{workers},{'MATCH' if same else 'MISMATCH'}")
+
+path = OUT / "determinism-crossing-compare.log"
+path.write_text("\n".join(lines) + "\n", encoding="utf-8")
+print("\n".join(lines))
+print(f"[L31CrossingHashCompare] comparisons={len(lines)} "
+      f"pass={sum(line.endswith('MATCH') for line in lines)} fail={sum(line.endswith('MISMATCH') for line in lines)}")
+raise SystemExit(1 if failed else 0)