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/EncodeCapturesL31.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+"""Encode the six requested L31 screenshots as small, pinned JPEGs."""
+import subprocess
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[4]
+SOURCE = ROOT / "Saved/Linux/l31"
+DEST = Path(__file__).resolve().parent / "captures"
+DEST.mkdir(parents=True, exist_ok=True)
+names = (
+    "fi-column-top-close-v19",
+    "fi-column-top-wide-v19",
+    "fi-column-base-close-v19",
+    "fi-column-base-wide-v19",
+    "fi-floor-v19-tint-off",
+    "fi-floor-v19-tint-on",
+)
+failed = False
+for name in names:
+    source = SOURCE / f"{name}.png"
+    destination = DEST / f"{name.removesuffix('-v19').replace('-v19-', '-')}.jpg"
+    command = [
+        "taskset", "-c", "0-11", "prlimit", "--as=6442450944", "--", "ffmpeg",
+        "-y", "-hide_banner", "-loglevel", "error", "-i", str(source),
+        "-frames:v", "1", "-q:v", "4", str(destination),
+    ]
+    result = subprocess.run(command, check=False)
+    size = destination.stat().st_size if destination.exists() else 0
+    ok = result.returncode == 0 and size <= 300_000
+    failed |= not ok
+    print(f"[L31CaptureJPEG] source={source.name} output={destination.name} "
+          f"bytes={size} status={'PASS' if ok else 'FAIL'}")
+raise SystemExit(1 if failed else 0)