diff --git a/tests/test_nat_detection.c b/tests/test_nat_detection.c
index 1f542366..06fc0a27 100644
--- a/tests/test_nat_detection.c
+++ b/tests/test_nat_detection.c
@@ -210,6 +210,16 @@ static void test_tcp_presence(void) {
     DEBUG_INFO(DEBUG_CATEGORY_NAT, "PASS TCP NAT presence: one peer, public/private IP, ignored ports, signed IP:0 and SQLite");
 }
 
+/* Прямое подключение helper к owner подтвердило бы OPEN вместо нового измерения через next hop. */
+static void block_owner_link(struct ETCP_CONN* conn, struct ETCP_LINK* link, int old_state, int old_status, void* arg) {
+    (void)old_status;
+    struct UTUN_INSTANCE* owner = arg;
+    if (old_state != -1 || conn->peer_node_id != owner->node_id) return;
+    DEBUG_INFO(DEBUG_CATEGORY_NAT, "NAT test: block helper direct transport to owner node=%016llx protocol=%s",
+               (unsigned long long)owner->node_id, link->is_tcp ? "TCP" : "UDP");
+    etcp_link_close(link);
+}
+
 /* Недостаточная UTUN-группа и достаточная CHAT-группа; helper доступен только через TCP next hop. */
 static void test_all_groups_tcp(void) {
     struct nat_fixture fixture; nat_fixture_init(&fixture);
@@ -267,6 +277,7 @@ static void test_all_groups_tcp(void) {
     assert(!instance_find_conn(owner, helper->node_id));
     /* Реально заблокированный UDP endpoint: UNKNOWN не запускает лишних проверок, подписанный OPEN запускает одну. */
     uint64_t verified_round = status.round;
+    etcp_add_link_status_cbk(helper, block_owner_link, owner);
     struct NODE_CONN_DIRECT **failed_handle = &fixture.handles[fixture.handle_count++];
     node = topo_node_registry_find(owner->topo_groups, helper->node_id);
     assert(node_conn_direct_open_node(owner, helper->node_id, NULL, NULL, failed_handle, node, socket) != NCD_ERR);
@@ -308,6 +319,7 @@ static void test_all_groups_tcp(void) {
     assert(!nat_detection_get_status(owner->nat_det, socket, &status) && !status.phase && !status.group_id);
     assert(socket->address_profile.mapping == ADDRESS_MAP_UNCHANGED && socket->address_profile.inbound == ADDRESS_IN_OPEN);
     assert(ab->links_up && topo_group_peer_ready(topo_groups_find(owner->topo_groups, TOPO_GROUP_UTUN), observer->node_id));
+    etcp_remove_link_status_cbk(helper, block_owner_link, owner);
     nat_fixture_cleanup(&fixture);
 }