feat: add topology graph v0.2.2 contract

tests/metadata.test.ts

@@ -22,6 +22,21 @@ test("crawl session id is unique for each generated graph", () => {
   assert.notEqual(first.metadata.crawlSessionId, second.metadata.crawlSessionId);
 });
 
+test("empty graph starts with a machine-readable summary", () => {
+  const graph = buildEmptyGraph(graphArgs);
+
+  assert.deepEqual(graph.summary, {
+    states: 0,
+    elements: 0,
+    edges: 0,
+    skippedActions: 0,
+    failedObservations: 0,
+    failedObservationsByReason: {},
+    skippedActionsByRiskCategory: {},
+    edgesByRiskCategory: {},
+  });
+});
+
 function withFixedDate<T>(callback: () => T): T {
   const RealDate = Date;
   const fixedTime = new RealDate("2026-06-16T00:00:00.000Z").getTime();