wip: opt-in landing-pad contract + Core.Liminal.Field v2 pads (L145)

Layers may publish certified arrival/departure pads; the passage planner binds endpoints and tangents to them;
no-pad layouts serialize unchanged (owner canonical hashes match v227). Pads removed the endpoint grade failures;
seeds 0-4 passed at a 45 m margin, but seed 5 still has 289 blocked passage-capsule samples ~29 m before the
departure pad, where the composed field stays solid (-0.162) inside the tube over native ground (-3.6). Ripple
audit now keeps true route distance across masked gaps (with a synthetic control).

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

Standalone/Research/WorldAssemblerM3/Linux145/BuildL145Fixtures.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+"""Build the 3-strata composed Core.Liminal.Field v2 fixture."""
+from __future__ import annotations
+
+import argparse
+import json
+import os
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[4]
+OWNER = Path(os.environ.get("VOXELFORGE_OWNER_DATA",
+                            ROOT / "Standalone/data/owner_world.json"))
+OUT_DEFAULT = Path(os.environ.get("VOXELFORGE_VERIFY_OUT", ROOT / "Saved/Linux/l145"))
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--out", type=Path, default=OUT_DEFAULT / "fixtures")
+    args = parser.parse_args()
+    args.out.mkdir(parents=True, exist_ok=True)
+    world = json.loads(OWNER.read_text(encoding="utf-8"))
+    if len(world.get("strates", [])) < 3:
+        raise SystemExit("owner fixture needs at least three authored strate slots")
+
+    world["strates"] = world["strates"][:3]
+    world["total_strates"] = 3
+    world["settings_asset"]["TotalStrates"] = 3
+    world["settings_asset"]["FixedStrates"] = world["settings_asset"]["FixedStrates"][:3]
+    # Keep the resolved arrival near the departure depth. The owner's 5000-unit
+    # reach clamps to liminal bedrock on most seeds and leaves no field floor.
+    world["strates"][0]["passage_config"]["ReachMin"] = 1536
+    world["strates"][0]["passage_config"]["ReachMax"] = 1792
+    world["surface_profile_override"] = {
+        "version": 1,
+        "kind": "flatField",
+        "minimum_arena_clearance_m": 0.0,
+    }
+    middle = world["strates"][1]
+    middle["asset"]["GeneratorType"] = 4  # ECaveGeneratorType::SurfaceWorld
+    middle["asset"]["StrateName"] = "Liminal Field"
+    # Keep the departure mouth 24–32 m above liminal bedrock so every variant
+    # has room for its floor, road landing and support footings.
+    middle["passage_config"]["ReachMin"] = 192
+    middle["passage_config"]["ReachMax"] = 256
+    world["core_liminal_field"] = {
+        "version": 2,
+        "strate_index": int(middle["index"]),
+        "variant_policy": "seed_modulo_4",
+    }
+
+    output = args.out / "core-liminal-field-3-strata.json"
+    output.write_text(json.dumps(world, separators=(",", ":")) + "\n", encoding="utf-8")
+    print(f"[L145Fixture] path={output} strates=SurfaceWorld,Core.Liminal.Field,TunnelNetwork status=PASS")
+
+
+if __name__ == "__main__":
+    main()