Refactor: Enforce type safety, fix close deadlock, implement assignee restrictions and notify admin fallbacks

tests/Feature/TransferFlowTest.php

@@ -119,3 +119,44 @@ test('transfer without reason throws validation error', function () {
 
     expect(TicketTransferLog::count())->toBe(0);
 });
+
+// ─── Transfer to invalid handler should fail ─────────────────────────
+test('transfer to handler not in target department throws validation error', function () {
+    $managerRole = Role::create(['name' => 'manager']);
+    $managerRole->givePermissionTo(['transfer-department', 'view-feedback', 'create-feedback', 'update-feedback']);
+
+    $sender = User::factory()->create();
+    $sender->assignRole('manager');
+
+    $fromDept = Department::create(['name' => 'CSKH']);
+    $toDept = Department::create(['name' => 'Ky Thuat']);
+
+    // Handler belongs to Finance department
+    $financeDept = Department::create(['name' => 'Tai Chinh']);
+    $handler = User::factory()->create(['department_id' => $financeDept->id]);
+
+    $channel = FeedbackChannel::create(['name' => 'Phone', 'slug' => 'phone-transfer']);
+    $customer = Customer::create(['name' => 'Test', 'email' => 't@test.com']);
+
+    $feedback = Feedback::create([
+        'customer_id' => $customer->id,
+        'feedback_channel_id' => $channel->id,
+        'title' => 'Transfer To Invalid Handler',
+        'content' => 'Test',
+        'status' => 'pending',
+        'current_department_id' => $fromDept->id,
+    ]);
+
+    $this->actingAs($sender);
+
+    $transferService = app(TransferService::class);
+
+    try {
+        $transferService->transfer($feedback, $toDept, 'Chuyen sang kiem tra', $sender, $handler->id);
+        $this->fail('Expected ValidationException but none thrown.');
+    } catch (\Illuminate\Validation\ValidationException $e) {
+        expect($e->errors()['new_assignee_id'][0])->toContain('Người xử lý được chọn không thuộc phòng ban đích');
+    }
+
+    expect(TicketTransferLog::count())->toBe(0);
+});