feat(FN-4041): harden empty rawResponse handling in memory-insights

Hardened empty `rawResponse` handling in the memory insights module by adding defensive checks to prevent errors when the response is empty, accompanied by tests to cover those edge cases (FN-4041 Step 1).

Fusion-Task-Id: FN-4041

packages/engine/src/__tests__/triage.test.ts

@@ -1623,6 +1623,53 @@ describe("approved triage recovery", () => {
     );
   });
 
+  it("preserves imported GitHub issue titles during planning recovery", async () => {
+    await writeFile(
+      join(rootDir, ".fusion", "tasks", "FN-001", "PROMPT.md"),
+      "# Task: FN-001 - Different AI-generated planning title\n\n**Size:** M\n\n## Review Level: 2\n\nRecovered specification",
+    );
+
+    const store = createMockStore({
+      getSettings: vi.fn().mockResolvedValue({
+        maxConcurrent: 2,
+        maxWorktrees: 4,
+        pollIntervalMs: 10000,
+        groupOverlappingFiles: false,
+        autoMerge: true,
+        requirePlanApproval: false,
+      } as Settings),
+    });
+
+    const processor = new TriageProcessor(store, rootDir);
+    const recovered = await processor.recoverApprovedTask({
+      id: "FN-001",
+      description: "Imported from GitHub",
+      column: "triage",
+      status: "planning",
+      title: '"Cannot read properties of undefined (reading \'trim\')" when extracting insights',
+      sourceType: "github_import",
+      sourceIssue: {
+        provider: "github",
+        repository: "Runfusion/Fusion",
+        externalIssueId: "70",
+        issueNumber: 70,
+        url: "https://github.com/Runfusion/Fusion/issues/70",
+      },
+      dependencies: [],
+      steps: [],
+      currentStep: 0,
+      log: [{ timestamp: "2026-01-01T00:00:00.000Z", action: "Spec review: APPROVE" }],
+      createdAt: "2026-01-01T00:00:00.000Z",
+      updatedAt: "2026-01-01T00:02:00.000Z",
+    });
+
+    expect(recovered).toBe(true);
+    expect(store.updateTask).not.toHaveBeenCalledWith(
+      "FN-001",
+      expect.objectContaining({ title: "Different AI-generated planning title" }),
+    );
+  });
+
   it("clears status and error before moving approved tasks to todo", async () => {
     const store = createMockStore({
       getSettings: vi.fn().mockResolvedValue({