Unify UME World as hex nav with conditional flat world map.

Seed a unique L2 World canvas under the UME World container, show the flat map only when nested regions have NEs, pack blocks without overlap, allow drag overrides on the world map while forbidding direct NE adds, and hide the world-map truncation banner.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_topology.py

@@ -480,7 +480,7 @@ class FabricTopologyTests(unittest.TestCase):
         tree = svc.get_topology_tree(self.db)
         assert tree.root is not None
         reg = next(c for c in tree.root.children if c.id == region.id)
-        self.assertEqual(len(reg.views), 1)
+        self.assertTrue(any(v.id == custom.id for v in reg.views))
 
         out = svc.delete_folder(self.db, region.id)
         self.assertTrue(out.get("deleted"))
@@ -493,6 +493,53 @@ class FabricTopologyTests(unittest.TestCase):
             0,
         )
 
+    def test_nested_region_places_icon_on_parent_canvas(self) -> None:
+        parent = svc.create_folder(
+            self.db, TopologyFolderCreate(name="Parent-Canvas", kind="region")
+        )
+        child = svc.create_folder(
+            self.db,
+            TopologyFolderCreate(name="Child-Icon", kind="region", parent_id=parent.id),
+        )
+        tree = svc.get_topology_tree(self.db)
+        assert tree.root is not None
+        p = next(c for c in tree.root.children if c.id == parent.id)
+        self.assertTrue(p.views)
+        graph = svc.get_view_graph(self.db, p.views[0].id)
+        regions = [n for n in graph.nodes if n.kind == "region"]
+        self.assertEqual(len(regions), 1)
+        self.assertEqual(regions[0].folder_id, child.id)
+        self.assertEqual(regions[0].label, "Child-Icon")
+        self.assertTrue(str(regions[0].fabric_node_id).startswith("region:"))
+
+        # Drag/save positions for synthetic region nodes.
+        moved = svc.patch_view_positions(
+            self.db,
+            p.views[0].id,
+            ViewPositionsPatch(
+                positions=[
+                    ViewNodeIn(
+                        fabric_node_id=regions[0].fabric_node_id, x=321, y=210
+                    )
+                ],
+                return_graph=True,
+            ),
+        )
+        if hasattr(moved, "nodes"):
+            hit = next(n for n in moved.nodes if n.kind == "region")
+        else:
+            hit = next(
+                n
+                for n in svc.get_view_graph(self.db, p.views[0].id).nodes
+                if n.kind == "region"
+            )
+        self.assertEqual(hit.x, 321)
+        self.assertEqual(hit.y, 210)
+
+        svc.delete_folder(self.db, child.id)
+        graph2 = svc.get_view_graph(self.db, p.views[0].id)
+        self.assertFalse(any(n.kind == "region" for n in graph2.nodes))
+
     def test_classify_role_region_and_slices(self) -> None:
         from netx_api import topology_classify as clf
         from netx_api.topology_schemas import (