Reproduce ACK starvation behind the reverse-direction DATA pacer

tests/test_etcp_windows.c

@@ -307,6 +307,22 @@ static void immediate_send(void) {
     ack_all(); teardown();
 }
 
+/* Подтверждения входящего потока не должны ждать pacing собственного исходящего DATA. */
+static void ack_without_data_pacing(void) {
+    setup(); b->link_status = 0; a->bandwidth = 1;
+    a->shaper_timer = uasync_set_timeout(ua, 1000, a, shaper_ready, "test_shaper"); CHECK(a->shaper_timer);
+    void* timer = a->shaper_timer;
+    uint64_t load = a->shaper_load_time_tb, fraction = a->shaper_sub_nanotime;
+    struct ACK_PACKET* confirmation = (struct ACK_PACKET*)queue_entry_new_from_pool(inst.ack_pool); CHECK(confirmation);
+    confirmation->seq = 777;
+    CHECK(queue_data_put_with_index(conn->ack_q, &confirmation->ll) == 0);
+    enqueue(100); uasync_drain_immediate(ua);
+    CHECK(sends == 1 && conn->input_send_q->count == 1 && !conn->ack_q->count);
+    CHECK(a->shaper_timer == timer && a->shaper_load_time_tb == load && a->shaper_sub_nanotime == fraction);
+    uasync_cancel_timeout(ua, timer); a->shaper_timer = NULL;
+    etcp_conn_wake_sender(conn); wait_sends(2); ack_all(); teardown();
+}
+
 int main(void) {
     debug_config_init(); debug_set_level(DEBUG_LEVEL_ERROR);
     if (getenv("UTUN_TEST_DEBUG")) debug_set_category_level(DEBUG_CATEGORY_ETCP, DEBUG_LEVEL_DEBUG);
@@ -314,7 +330,7 @@ int main(void) {
     size_t baseline = u_get_allocated_count();
     void (*cases[])(void) = {selection, boundaries_ack_burst, late_ack_and_migration, lost_ack_and_shrink,
         grow_and_session, allocation_and_send_failure, removed_link_and_bbr, pacing_reset_close, initial_readiness,
-        config_limits, timer_failure, immediate_send};
+        config_limits, timer_failure, immediate_send, ack_without_data_pacing};
     for (unsigned i = 0; i < sizeof(cases) / sizeof(cases[0]); i++) {
         cases[i](); CHECK(u_get_allocated_count() == baseline);
         DEBUG_INFO(DEBUG_CATEGORY_DEBUG, "PASS ETCP window scenario %u", i);