feat: split RU-ARK into mainland + New Earth + Severnaya Zemlya — idempotent stage, manifests 1,798 (v0.25.0, #31)

scripts/region-adjacency.test.ts

@@ -34,7 +34,7 @@ describe('region-adjacency.json', () => {
     const adjacencyKeys = new Set(Object.keys(adjacency));
     expect(adjacencyKeys).toEqual(manifestKeys);
     expect(Object.keys(adjacency)).toHaveLength(keys.size);
-    expect(adjacencyKeys.size).toBe(1796);
+    expect(adjacencyKeys.size).toBe(1798);
   });
 
   it('every neighbour is itself a valid region key (referential integrity)', () => {
@@ -84,4 +84,26 @@ describe('region-adjacency.json', () => {
     expect(adjacency['moselle-rygy']?.includes('baden-wurttemberg-oyje')).toBe(true);
     expect(adjacency['baden-wurttemberg-oyje']?.includes('moselle-rygy')).toBe(true);
   });
+
+  it("the #31 island splits: New Earth is isolated; Severnaya Zemlya touches only the Arkhangel's main ring", () => {
+    // v0.25 (#31) split RU-ARK into the mainland (arkhangel-sk-lhbk), the
+    // Franz Josef Land islets (new-earth-eikt) and the Severnaya Zemlya
+    // islets (severnaya-zemlya-awqp). New Earth sits ~100+ km from any land
+    // → a genuinely isolated island (empty list). Severnaya Zemlya's
+    // digitized islet rings share boundary vertices with the coarsened
+    // mainland ring (a pre-existing intra-feature contact, exposed by the
+    // split) → it touches exactly its former parent, with no overlap area.
+    expect(adjacency['new-earth-eikt']).toEqual([]);
+    expect(adjacency['severnaya-zemlya-awqp']).toEqual(['arkhangel-sk-lhbk']);
+    // the mainland keeps its six real neighbours plus the island contact
+    expect(adjacency['arkhangel-sk-lhbk']).toEqual([
+      'karelia-ohem',
+      'kirov-gfvm',
+      'komi-eoeh',
+      'murmansk-etas',
+      'nenets-qyga',
+      'severnaya-zemlya-awqp',
+      'vologda-ynvr',
+    ]);
+  });
 });