fix(memory): reject dangling relations (#4477)

Signed-off-by: King Star <mcxin.y@gmail.com>

src/memory/README.md

@@ -72,6 +72,7 @@ Example:
       - `to` (string): Target entity name
       - `relationType` (string): Relationship type in active voice
   - Skips duplicate relations
+  - Fails if either the source or target entity doesn't exist
 
 - **add_observations**
   - Add new observations to existing entities

src/memory/__tests__/knowledge-graph.test.ts

@@ -99,6 +99,38 @@ describe('KnowledgeGraphManager', () => {
       expect(graph.relations).toHaveLength(1);
     });
 
+    it('should reject relations from non-existent entities', async () => {
+      await manager.createEntities([
+        { name: 'Alice', entityType: 'person', observations: [] },
+      ]);
+
+      await expect(
+        manager.createRelations([
+          { from: 'Ghost', to: 'Alice', relationType: 'knows' },
+        ])
+      ).rejects.toThrow('Entity with name Ghost not found');
+
+      const graph = await manager.readGraph();
+      expect(graph.relations).toHaveLength(0);
+    });
+
+    it('should reject relation batches that reference non-existent target entities', async () => {
+      await manager.createEntities([
+        { name: 'Alice', entityType: 'person', observations: [] },
+        { name: 'Bob', entityType: 'person', observations: [] },
+      ]);
+
+      await expect(
+        manager.createRelations([
+          { from: 'Alice', to: 'Bob', relationType: 'knows' },
+          { from: 'Alice', to: 'Ghost', relationType: 'knows' },
+        ])
+      ).rejects.toThrow('Entity with name Ghost not found');
+
+      const graph = await manager.readGraph();
+      expect(graph.relations).toHaveLength(0);
+    });
+
     it('should handle empty relation arrays', async () => {
       const newRelations = await manager.createRelations([]);
       expect(newRelations).toHaveLength(0);

src/memory/index.ts

@@ -151,6 +151,17 @@ export class KnowledgeGraphManager {
 
   async createRelations(relations: Relation[]): Promise<Relation[]> {
     const graph = await this.loadGraph();
+    const entityNames = new Set(graph.entities.map(e => e.name));
+
+    relations.forEach(r => {
+      if (!entityNames.has(r.from)) {
+        throw new Error(`Entity with name ${r.from} not found`);
+      }
+      if (!entityNames.has(r.to)) {
+        throw new Error(`Entity with name ${r.to} not found`);
+      }
+    });
+
     const newRelations = relations.filter(r => !graph.relations.some(existingRelation => 
       existingRelation.from === r.from && 
       existingRelation.to === r.to &&