fix: preserve resolved flag when closing tickets

backend/apps/tickets/tests/test_ticket_api.py

@@ -192,6 +192,28 @@ def test_technical_ticket_cannot_be_resolved_directly(admin_client, db):
     assert response.status_code == 400
 
 
+def test_closing_resolved_ticket_keeps_resolved_flag(admin_client, db):
+    ticket = Ticket.objects.create(
+        ticket_no="TK202607010106",
+        title="已解决待关闭",
+        description="A",
+        status="resolved",
+        is_resolved=True,
+        resolution_summary="已完成处理",
+    )
+
+    response = admin_client.post(
+        f"/api/tickets/{ticket.id}/status",
+        data={"status": "closed", "remark": "已回复", "is_resolved": False},
+        content_type="application/json",
+    )
+
+    assert response.status_code == 200
+    ticket.refresh_from_db()
+    assert ticket.status == "closed"
+    assert ticket.is_resolved is True
+
+
 def test_get_ticket_events_returns_real_timeline_with_operator(admin_client, db):
     user_model = get_user_model()
     operator = user_model.objects.get(username="admin")