experiment: LivingPlane repeatable + standalone UE runtime module (L164)

Readback barrier fix (GL_TEXTURE_UPDATE_BARRIER_BIT before glGetTexImage); check_repeatability.py compares full-field
checksums across query/capture settings - Intel GPU PASS (3b9d45905c7aafff), llvmpipe PASS, mismatch control fails.
New runtime module VoxelForgeLivingPlane (separate from generation): RDG global shader (Shaders/LivingPlane.usf),
ping-pong RGBA32F render targets, actor with WPO plane and object inputs, no CPU readback. Compiles in Linux UE 5.7.
Windows build: Source/VoxelForgeLivingPlane/*, Shaders/LivingPlane.usf, VoxelForge.uplugin. Setup: UE-SETUP.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Experiments/LivingPlane/check_repeatability.py

@@ -0,0 +1,132 @@
+#!/usr/bin/env python3
+"""Compare final field checksums across different query and capture settings."""
+
+from __future__ import annotations
+
+import argparse
+import json
+import pathlib
+import shutil
+import subprocess
+import sys
+
+
+PLUGIN_ROOT = pathlib.Path(__file__).resolve().parents[2]
+
+
+def read_checksum(path: pathlib.Path) -> str:
+    try:
+        with path.open(encoding="utf-8") as source:
+            result = json.load(source)
+    except (OSError, json.JSONDecodeError) as error:
+        raise RuntimeError(f"could not read {path}: {error}") from error
+    checksum = result.get("field_checksum_fnv1a64")
+    if not isinstance(checksum, str) or len(checksum) != 16:
+        raise RuntimeError(f"{path} has no 16-digit field checksum")
+    return checksum
+
+
+def compare(left: pathlib.Path, right: pathlib.Path) -> bool:
+    left_checksum = read_checksum(left)
+    right_checksum = read_checksum(right)
+    if left_checksum != right_checksum:
+        print(
+            "FAIL field checksum mismatch: "
+            f"{left}={left_checksum}, {right}={right_checksum}",
+            file=sys.stderr,
+        )
+        return False
+    print(f"PASS field checksum matches: {left_checksum}")
+    return True
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--binary",
+        type=pathlib.Path,
+        default=PLUGIN_ROOT / "Saved/Linux/l164/living-plane",
+    )
+    parser.add_argument(
+        "--out",
+        type=pathlib.Path,
+        default=PLUGIN_ROOT / "Saved/Linux/l164/repeatability",
+    )
+    parser.add_argument("--device", choices=("auto", "cpu", "gpu"), default="cpu")
+    parser.add_argument("--size", type=int, default=512)
+    parser.add_argument("--steps", type=int, default=1800)
+    parser.add_argument(
+        "--compare-only",
+        nargs=2,
+        type=pathlib.Path,
+        metavar=("LEFT_JSON", "RIGHT_JSON"),
+        help="compare existing timing.json files; used to exercise the failure path",
+    )
+    options = parser.parse_args()
+
+    if options.compare_only:
+        return 0 if compare(*options.compare_only) else 1
+
+    if not options.binary.is_file():
+        parser.error(f"binary not found: {options.binary}; run Experiments/LivingPlane/build.sh")
+
+    options.out.mkdir(parents=True, exist_ok=True)
+    off_dir = options.out / "queries-off_capture-off"
+    on_dir = options.out / "queries-on_capture-every-900"
+    for directory in (off_dir, on_dir):
+        if directory.exists():
+            shutil.rmtree(directory)
+
+    common = [
+        f"--device={options.device}",
+        "--scene=alive",
+        f"--size={options.size}",
+        f"--steps={options.steps}",
+    ]
+    runs = (
+        ("--capture-every=0", "--queries=off", off_dir),
+        ("--capture-every=900", "--queries=on", on_dir),
+    )
+    for capture, queries, output in runs:
+        command = [
+            "taskset",
+            "-c",
+            "0-11",
+            "prlimit",
+            "--as=6442450944",
+            "--",
+            "timeout",
+            "1740s",
+            str(options.binary.resolve()),
+            *common,
+            capture,
+            queries,
+            f"--out={output}",
+        ]
+        print("RUN " + " ".join(command), flush=True)
+        log_path = options.out / f"{output.name}.log"
+        with log_path.open("w", encoding="utf-8") as log_file:
+            try:
+                subprocess.run(
+                    command,
+                    cwd=PLUGIN_ROOT,
+                    check=True,
+                    stdout=log_file,
+                    stderr=subprocess.STDOUT,
+                )
+            except subprocess.CalledProcessError:
+                print(log_path.read_text(encoding="utf-8"), file=sys.stderr)
+                raise
+        print(log_path.read_text(encoding="utf-8").rstrip())
+
+    left = off_dir / "timing.json"
+    right = on_dir / "timing.json"
+    return 0 if compare(left, right) else 1
+
+
+if __name__ == "__main__":
+    try:
+        raise SystemExit(main())
+    except (OSError, RuntimeError, subprocess.CalledProcessError) as error:
+        print(f"FAIL repeatability check: {error}", file=sys.stderr)
+        raise SystemExit(1)