proto: liminal pass 2 - hills to the horizon, swept road over a cloud floor, pillar grid (L142)

Captures stream LOD0-8 (hills repeat at 80 m to the horizon). Road: cubic swept solid deck, 376.8 m, 8 m wide, max
12.06 deg, 17 supports, cloud floor ~45 m below; walk audit 0 blocked/unsupported, 300 m negative control fails as
expected. 15x15 identical pillar grid at 76 m. Owner canonical hashes unchanged; fast tier, Clang/GCC green.

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

Standalone/Research/WorldAssemblerM3/Linux142/BuildL142Fixtures.py

@@ -0,0 +1,113 @@
+#!/usr/bin/env python3
+"""Build the L142 liminal pictures and walk-audit controls."""
+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/l142"))
+
+FLAT_FIELD = {
+    "version": 1,
+    "kind": "flatField",
+    "minimum_arena_clearance_m": 0.0,
+}
+
+
+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)
+    base = json.loads(OWNER.read_text(encoding="utf-8"))
+
+    monolith = dict(base)
+    monolith["surface_profile_override"] = dict(FLAT_FIELD)
+    monolith["motif_family_override"] = {
+        "version": 1,
+        "strate_index": 0,
+        "placement_policy": "seed,strate,stable_id",
+        "motifs": [{
+            "stable_id": "liminal/oversized-familiar-monolith-v1",
+            "kind": "cappedCylinder",
+            "radius_m": 1.6,
+            "height_m": 26.0,
+            "route_side_offset_m": 42.0,
+            "placement_radius_m": 0.0,
+            "fillet_radius_m": 0.6,
+            "blend_width_m": 1.2,
+            "minimum_spacing_m": 0.0,
+            "yaw_quarter_turns": 0,
+            "attachment": "seated_floor",
+        }],
+    }
+
+    hills = dict(base)
+    hills["surface_profile_override"] = {
+        "version": 1,
+        "kind": "periodicHills",
+        "amplitude_x_m": 2.2,
+        "amplitude_y_m": 2.2,
+        "wavelength_x_m": 80.0,
+        "wavelength_y_m": 80.0,
+        "minimum_arena_clearance_m": 0.0,
+    }
+
+    road_override = {
+        "stable_id": "liminal/road-clouds-v2",
+        "strate_index": 0,
+        "start_xy_m": [120.0, 340.0],
+        "path_length_m": 360.0,
+        "curve_control_offset_m": 84.0,
+        "deck_height_above_field_m": 44.0,
+        "rise_control_m": 22.0,
+        "half_width_m": 4.0,
+        "half_thickness_m": 1.0,
+        "sample_spacing_m": 2.0,
+        "support_spacing_m": 24.0,
+        "support_radius_m": 0.55,
+    }
+    road = dict(base)
+    road["surface_profile_override"] = dict(FLAT_FIELD)
+    road["liminal_road_override"] = dict(road_override)
+
+    short_control = dict(base)
+    short_control["surface_profile_override"] = dict(FLAT_FIELD)
+    short_override = dict(road_override)
+    short_override["path_length_m"] = 180.0
+    short_control["liminal_road_override"] = short_override
+
+    pillars = dict(base)
+    pillars["surface_profile_override"] = dict(FLAT_FIELD)
+    pillars["liminal_pillar_grid_override"] = {
+        "stable_id": "liminal/horizon-pillar-grid-v1",
+        "strate_index": 0,
+        "center_xy_m": [700.0, 800.0],
+        "rows": 15,
+        "columns": 15,
+        "spacing_m": 76.0,
+        "radius_m": 5.5,
+        "height_m": 40.0,
+    }
+
+    fixtures = (
+        ("flatField-monolith", monolith),
+        ("periodicHills", hills),
+        ("road-in-clouds", road),
+        ("road-short-control", short_control),
+        ("pillar-grid", pillars),
+    )
+    for name, fixture in fixtures:
+        path = args.out / f"liminal-{name}.json"
+        path.write_text(json.dumps(fixture, indent=2) + "\n", encoding="utf-8")
+        print(f"[L142Fixture] name={name} file={path} status=PASS")
+
+
+if __name__ == "__main__":
+    main()