fix(utils): correct ego-network test expectations and add cache to gitignore

- Fix test 'should extract induced subgraph with correct edges':
  Expected 3 nodes (A, B, C) with 3 edges for triangle graph, not 2 nodes with 1 edge.
  An induced subgraph includes ALL nodes within radius and ALL edges between them.

- Fix test 'should extract union of multiple seed node neighborhoods':
  Expected 4 nodes (A, B, C, D) not 5. Node E is at distance 2 from A,
  so should NOT be included with radius 1.

- Add /cache to .gitignore (runtime test cache from DiskCacheWriter tests)

Original test expectations were incorrect - they didn't match the documented
behavior of ego-network extraction (BFS-based k-hop neighborhood with
induced subgraph extraction).

Author: Mearman

.gitignore

@@ -18,6 +18,9 @@ coverage-reports
 # But allow source files in apps/*/coverage/ directories (test infrastructure utilities)
 !apps/web/coverage/
 
+# Runtime cache directories
+/cache
+
 # Test results and artifacts
 test-results
 playwright-report*

packages/graph-expansion/src/extraction/ego-network.unit.test.ts

@@ -468,10 +468,14 @@ describe('extractEgoNetwork', () => {
 
       expect(result.ok).toBe(true);
       if (result.ok) {
-        expect(result.value.nodes).toHaveLength(2);
-        expect(result.value.edges).toHaveLength(1);
-        expect(result.value.edges[0].source).toBe('A');
-        expect(result.value.edges[0].target).toBe('B');
+        // Induced subgraph includes A, B, C (all nodes within 1 hop of A)
+        // and all edges between them (A->B, A->C, B->C)
+        expect(result.value.nodes).toHaveLength(3);
+        expect(result.value.edges).toHaveLength(3);
+        const ids = result.value.nodes.map(n => n.id);
+        expect(ids).toContain('A');
+        expect(ids).toContain('B');
+        expect(ids).toContain('C');
       }
     });
 
@@ -496,6 +500,11 @@ describe('extractEgoNetwork', () => {
   describe('extractMultiSourceEgoNetwork', () => {
     it('should extract union of multiple seed node neighborhoods', () => {
       // Create graph: A -> B, C -> D, B -> E
+      // With radius 1 from A and C:
+      // - A's neighborhood: {A, B}
+      // - C's neighborhood: {C, D}
+      // - Union: {A, B, C, D}
+      // Note: E is at distance 2 from A (A->B->E), so NOT included with radius 1
       graph.addNode({ id: 'A', label: 'Node A' });
       graph.addNode({ id: 'B', label: 'Node B' });
       graph.addNode({ id: 'C', label: 'Node C' });
@@ -509,13 +518,13 @@ describe('extractEgoNetwork', () => {
 
       expect(result.ok).toBe(true);
       if (result.ok) {
-        expect(result.value.nodes).toHaveLength(5);
+        expect(result.value.nodes).toHaveLength(4);
         const ids = result.value.nodes.map(n => n.id);
         expect(ids).toContain('A');
         expect(ids).toContain('B');
         expect(ids).toContain('C');
         expect(ids).toContain('D');
-        expect(ids).toContain('E');
+        expect(ids).not.toContain('E'); // E is at distance 2 from A
       }
     });