Verify ACK deadlines through link down and removal

tests/test_etcp_windows.c

@@ -1264,6 +1264,28 @@ static void ack_sender_failure(void) {
     etcp_conn_ref_free(conn); teardown();
 }
 
+/* DOWN не мешает срокам других путей; UP возвращает старые ACK сразу. Удаление головы не оставляет чужой deadline. */
+static void ack_link_lifecycle(void) {
+    for (unsigned remove = 0; remove < 2; remove++) {
+        setup(); conn->got_initial_pkt = 1;
+        ack_now_us = get_time_us(); ack_clock_active = 1;
+        uint64_t begin = ack_now_us;
+        receive_fragment(a, 2, 1); ack_now_us += 1000; receive_fragment(b, 3, 1);
+        if (remove) { etcp_link_close(a); a = NULL; }
+        else a->link_status = 0;
+        ack_now_us = begin + 2000; CHECK(!request() && conn->ack_resp_deadline_us == begin + 3000);
+        ack_now_us = begin + 3000;
+        struct ETCP_DGRAM* pkt = request(); CHECK(pkt && pkt->link == b && pkt->data[1] == 1);
+        memory_pool_free(inst.pkt_pool, pkt); CHECK(!conn->ack_resp_timer);
+        if (!remove) {
+            a->link_status = 1; etcp_conn_wake_sender(conn);
+            pkt = request(); CHECK(pkt && pkt->link == a && pkt->data[1] == 1);
+            memory_pool_free(inst.pkt_pool, pkt);
+        }
+        teardown();
+    }
+}
+
 static void receive_admission_and_path_acks(void) {
     setup(); conn->got_initial_pkt = 1;
     fail_rx_data = 1; receive_fragment(a, 2, 1);
@@ -1690,7 +1712,7 @@ int main(void) {
         send_queue_scan, send_queue_input_admission,
         retry_full_round_history, retry_history_slot_reuse, fast_stall_progress, stalled_retry_selection, input_admission_callbacks,
         ack_absolute_deadline, ack_piggyback_deadlines, ack_partial_piggyback, ack_timer_interleaving,
-        ack_urgent_and_oom, ack_partial_frame_and_lifecycle, ack_sender_failure,
+        ack_urgent_and_oom, ack_partial_frame_and_lifecycle, ack_sender_failure, ack_link_lifecycle,
         receive_admission_and_path_acks, peer_window_queries, pacing_continuity, pacing_data_units, attempt_memory_limits,
         normalizer_rx_oom, normalizer_tx_oom, normalizer_callback_abort, reset_without_allocation, restart_allocation_failures,
         receiver_bandwidth_bounds, receiver_point_lifecycle, receiver_point_wire, receiver_point_truncated,