fix(memory): validate knowledge graph entries when loading from disk (#4717)

loadGraph() trusted the persisted memory file and pushed entities and
relations without validating their fields. A corrupted or legacy entry
(e.g. an entity missing entityType, or an observation that is not a string)
would reach searchNodes and crash with "Cannot read properties of undefined
(reading 'toLowerCase')".

Validate each line against the existing EntitySchema/RelationSchema and skip
malformed entries with a warning, so the in-memory graph only ever contains
well-formed data. Malformed JSON lines are skipped as well.

Fixes #2044

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

@@ -617,4 +617,51 @@ describe('KnowledgeGraphManager', () => {
       expect(result.relations[0]).not.toHaveProperty('type');
     });
   });
+
+  describe('loadGraph validation', () => {
+    it('skips corrupt entities instead of crashing search', async () => {
+      const lines = [
+        JSON.stringify({ type: 'entity', name: 'Alice', entityType: 'person', observations: ['works at Acme Corp'] }),
+        JSON.stringify({ type: 'entity', name: 'Broken', observations: ['missing entityType'] }),
+        JSON.stringify({ type: 'entity', name: 'BadObs', entityType: 'person', observations: ['ok', null] }),
+      ];
+      await fs.writeFile(testFilePath, lines.join('\n') + '\n');
+
+      const graph = await manager.readGraph();
+      expect(graph.entities).toHaveLength(1);
+      expect(graph.entities[0].name).toBe('Alice');
+
+      // searchNodes must not throw even though the file contains corrupt entries
+      const result = await manager.searchNodes('Acme');
+      expect(result.entities).toHaveLength(1);
+      expect(result.entities[0].name).toBe('Alice');
+    });
+
+    it('skips corrupt relations', async () => {
+      const lines = [
+        JSON.stringify({ type: 'entity', name: 'Alice', entityType: 'person', observations: [] }),
+        JSON.stringify({ type: 'relation', from: 'Alice', to: 'Bob' }), // missing relationType
+        JSON.stringify({ type: 'relation', from: 'Alice', to: 'Bob', relationType: 'knows' }),
+      ];
+      await fs.writeFile(testFilePath, lines.join('\n') + '\n');
+
+      const graph = await manager.readGraph();
+      expect(graph.entities).toHaveLength(1);
+      expect(graph.relations).toHaveLength(1);
+      expect(graph.relations[0].relationType).toBe('knows');
+    });
+
+    it('skips malformed JSON lines', async () => {
+      const lines = [
+        JSON.stringify({ type: 'entity', name: 'Alice', entityType: 'person', observations: [] }),
+        '{this is not valid json',
+        JSON.stringify({ type: 'entity', name: 'Bob', entityType: 'person', observations: [] }),
+      ];
+      await fs.writeFile(testFilePath, lines.join('\n') + '\n');
+
+      const graph = await manager.readGraph();
+      expect(graph.entities).toHaveLength(2);
+      expect(graph.entities.map(e => e.name)).toEqual(['Alice', 'Bob']);
+    });
+  });
 });

src/memory/index.ts

@@ -90,24 +90,47 @@ export class KnowledgeGraphManager {
     try {
       const data = await fs.readFile(this.memoryFilePath, "utf-8");
       const lines = data.split("\n").filter(line => line.trim() !== "");
-      return lines.reduce((graph: KnowledgeGraph, line) => {
-        const item = JSON.parse(line);
-        if (item.type === "entity") {
-          graph.entities.push({
-            name: item.name,
-            entityType: item.entityType,
-            observations: item.observations
-          });
+      const graph: KnowledgeGraph = { entities: [], relations: [] };
+
+      for (const line of lines) {
+        let item: unknown;
+        try {
+          item = JSON.parse(line);
+        } catch {
+          console.error("Skipping malformed line in memory file");
+          continue;
         }
-        if (item.type === "relation") {
-          graph.relations.push({
-            from: item.from,
-            to: item.to,
-            relationType: item.relationType
-          });
+
+        if (typeof item !== "object" || item === null) {
+          console.error("Skipping non-object line in memory file");
+          continue;
         }
+
+        const record = item as Record<string, unknown>;
+        if (record.type === "entity") {
+          const parsed = EntitySchema.safeParse(item);
+          if (parsed.success) {
+            graph.entities.push(parsed.data);
+          } else {
+            console.error(
+              "Skipping invalid entity in memory file:",
+              parsed.error.issues.map(issue => `${issue.path.join(".")}: ${issue.message}`).join(", ")
+            );
+          }
+        } else if (record.type === "relation") {
+          const parsed = RelationSchema.safeParse(item);
+          if (parsed.success) {
+            graph.relations.push(parsed.data);
+          } else {
+            console.error(
+              "Skipping invalid relation in memory file:",
+              parsed.error.issues.map(issue => `${issue.path.join(".")}: ${issue.message}`).join(", ")
+            );
+          }
+        }
+      }
+
       return graph;
-      }, { entities: [], relations: [] });
     } catch (error) {
       if (error instanceof Error && 'code' in error && (error as any).code === "ENOENT") {
         return { entities: [], relations: [] };