fix(physics): validate retail cell containment roots

tests/AcDream.App.Tests/Rendering/CameraCollisionUpdateViewerTests.cs

@@ -71,10 +71,11 @@ public class CameraCollisionUpdateViewerTests
         var cache  = new PhysicsDataCache();
         var engine = new PhysicsEngine { DataCache = cache };
 
-        // Feet cell: interior Z ≤ 94, in its stab list the room cell above. No portals
-        // (so the collision sweep cannot transit to the room — the start cell is decisive).
+        // Feet cell: interior Z ≤ 94, in its stab list the room cell above.
+        // The inert sentinel portal keeps the synthetic cell eligible for
+        // retail CEnvCell::point_in_cell without creating a usable transit.
         cache.RegisterCellStructForTest(FeetCellId, MakeCell(InteriorZAtMost(94f), new uint[] { RoomCellId }));
-        // Room cell: interior Z ≥ 94, no walls, no portals.
+        // Room cell: interior Z ≥ 94, no walls and no usable portals.
         cache.RegisterCellStructForTest(RoomCellId, MakeCell(InteriorZAtLeast(94f), Array.Empty<uint>()));
 
         var heights     = new byte[81];
@@ -110,7 +111,7 @@ public class CameraCollisionUpdateViewerTests
         InverseWorldTransform = Matrix4x4.Identity,
         Resolved              = new Dictionary<ushort, ResolvedPolygon>(),
         CellBSP               = new CellBSPTree { Root = cellBspRoot },
-        Portals               = Array.Empty<PortalInfo>(),
+        Portals               = [new PortalInfo(0xFFFF, 0, 0)],
         PortalPolygons        = new Dictionary<ushort, ResolvedPolygon>(),
         VisibleCellIds        = new HashSet<uint>(visibleCellIds),
     };