chatgui: IPv4+IPv6 dual-stack listen by default

- Default config creates [server:lan] (0.0.0.0) + [server:lan6] ([::])
- Network settings save also writes [server:lan6] section
- Sets IPV6_V6ONLY=1 on IPv6 sockets to avoid conflict with IPv4
- interface_addr for [::] bind prefers permanent IPv6 over temporary

src/transport_layer/etcp_connections.c

@@ -557,6 +557,13 @@ struct ETCP_SOCKET* etcp_socket_add(struct UTUN_INSTANCE* instance, struct CFG_S
         DEBUG_WARN(DEBUG_CATEGORY_CONNECTION, "Failed to set non-blocking mode");
     }
 
+    if (family == AF_INET6) {
+        int v6only = 1;
+        if (setsockopt(e_sock->fd, IPPROTO_IPV6, IPV6_V6ONLY, &v6only, sizeof(v6only)) < 0) {
+            DEBUG_WARN(DEBUG_CATEGORY_CONNECTION, "Failed to set IPV6_V6ONLY: %s", socket_strerror(socket_get_error()));
+        }
+    }
+    
     // Set socket mark if specified (Linux only)
     if (so_mark > 0) {
         socket_set_mark(e_sock->fd, so_mark);
@@ -637,15 +644,28 @@ struct ETCP_SOCKET* etcp_socket_add(struct UTUN_INSTANCE* instance, struct CFG_S
         } else if (ip->ss_family == AF_INET6) {
             struct sockaddr_in6* sin6 = (struct sockaddr_in6*)ip;
             if (memcmp(&sin6->sin6_addr, &in6addr_any, sizeof(struct in6_addr)) == 0) {
-                // :: — определяем через default route
-                struct sockaddr_storage remote;
-                memset(&remote, 0, sizeof(remote));
-                struct sockaddr_in6* rem_sin6 = (struct sockaddr_in6*)&remote;
-                rem_sin6->sin6_family = AF_INET6;
-                rem_sin6->sin6_port = htons(53);
-                inet_pton(AF_INET6, "2001:4860:4860::8888", &rem_sin6->sin6_addr);
-                if (get_outgoing_local_ip(ip, &remote, &e_sock->interface_addr) != 0) {
-                    DEBUG_WARN(DEBUG_CATEGORY_CONNECTION, "Failed to detect outgoing local IPv6 for socket %s", e_sock->name);
+                // :: — приоритет: permanent > temporary > get_outgoing_local_ip
+                uint16_t v6if = (netif_index > 0) ? netif_index : get_default_route_netif_index(AF_INET6);
+                if (v6if > 0) {
+                    uint8_t v6addr[16];
+                    int got = get_interface_ipv6_by_index(v6if, 0, v6addr);
+                    if (got != 0) got = get_interface_ipv6_by_index(v6if, 1, v6addr);
+                    if (got == 0) {
+                        struct sockaddr_in6* if6 = (struct sockaddr_in6*)&e_sock->interface_addr;
+                        if6->sin6_family = AF_INET6;
+                        memcpy(&if6->sin6_addr, v6addr, 16);
+                    }
+                }
+                if (e_sock->interface_addr.ss_family == 0) {
+                    struct sockaddr_storage remote;
+                    memset(&remote, 0, sizeof(remote));
+                    struct sockaddr_in6* rem_sin6 = (struct sockaddr_in6*)&remote;
+                    rem_sin6->sin6_family = AF_INET6;
+                    rem_sin6->sin6_port = htons(53);
+                    inet_pton(AF_INET6, "2001:4860:4860::8888", &rem_sin6->sin6_addr);
+                    if (get_outgoing_local_ip(ip, &remote, &e_sock->interface_addr) != 0) {
+                        DEBUG_WARN(DEBUG_CATEGORY_CONNECTION, "Failed to detect outgoing local IPv6 for socket %s", e_sock->name);
+                    }
                 }
             }
         }

tools/chatgui/src/networksettingspage.cpp

@@ -140,6 +140,11 @@ void NetworkSettingsPage::saveToConfig(const QString& configPath) const {
     config_update_option(configPath, SECTION, "transport",
                          m_protoCombo->currentText().toLower(),
                          CONFIG_UPDATE_REPLACE);
+
+    // IPv6 dual-stack: always add [server:lan6] with same port
+    config_update_option(configPath, "server:lan6", "addr",
+                         QString("[::]:%1").arg(m_portSpin->value()),
+                         CONFIG_UPDATE_REPLACE);
 }
 
 void NetworkSettingsPage::onInterfaceChanged(int index) {

tools/chatgui/transport/node_config.cpp

@@ -177,8 +177,10 @@ bool NodeConfig::create(const QString& nodeName, quint16 listenPort) {
         m_controlAddr = "127.0.0.1:9999";
     m_servers.clear();
     m_clients.clear();
-    if (listenPort > 0)
+    if (listenPort > 0) {
         m_servers.append({"lan", QString("0.0.0.0:%1").arg(listenPort)});
+        m_servers.append({"lan6", QString("[::]:%1").arg(listenPort)});
+    }
     if (m_dbPath.isEmpty())
         m_dbPath = "chat_data";
     return save();