Fix DNS discovery: publish _config TXT under NS hostname, not just node ID

The server node ID fix (v0.6.4) changed the _config TXT record from
_config.ns1.lemonade-nexus.io to _config.server-0edf40003dfe0f7a.
Clients query _config.<ns_hostname> so they got NXDOMAIN.
Now publishes under BOTH the NS prefix (ns1) and the node ID.

Author: Geramy

projects/LemonadeNexus/src/main.cpp

@@ -398,17 +398,34 @@ int main(int argc, char* argv[]) {
 
     acme.set_dns_service(&dns);
 
-    // Publish _config TXT record (gossip-synced)
+    // Publish _config TXT records (gossip-synced)
+    // The NS hostname (e.g. "ns1") is what clients use for DNS discovery.
+    // Also publish under the server node ID for gossip-based discovery.
     {
-        std::string config_id = nexus::core::resolve_server_node_id(storage);
-        if (config_id.empty() && !config.server_hostname.empty()) {
-            config_id = config.server_hostname;
+        std::string config_fqdn = nexus::core::build_server_fqdn(
+            config.server_hostname, config.dns_base_domain);
+
+        // Determine the NS hostname prefix (e.g. "ns1" from "ns1.lemonade-nexus.io")
+        std::string ns_prefix;
+        std::string ns_fqdn = config.dns_ns_hostname;
+        if (ns_fqdn.empty() && !config.server_hostname.empty()) {
+            ns_prefix = config.server_hostname;
+        } else if (!ns_fqdn.empty()) {
+            auto dot = ns_fqdn.find('.');
+            ns_prefix = (dot != std::string::npos) ? ns_fqdn.substr(0, dot) : ns_fqdn;
         }
-        if (!config_id.empty()) {
-            std::string config_fqdn = nexus::core::build_server_fqdn(
-                config.server_hostname, config.dns_base_domain);
-            dns.publish_port_config(config_id, config_fqdn);
-            spdlog::info("DNS: published _config TXT for {} (host={})", config_id, config_fqdn);
+
+        // Publish under NS hostname prefix (for client DNS discovery: _config.ns1.domain)
+        if (!ns_prefix.empty()) {
+            dns.publish_port_config(ns_prefix, config_fqdn);
+            spdlog::info("DNS: published _config TXT for {} (host={})", ns_prefix, config_fqdn);
+        }
+
+        // Also publish under server node ID (for gossip-based server discovery)
+        std::string node_id = nexus::core::resolve_server_node_id(storage);
+        if (!node_id.empty() && node_id != ns_prefix) {
+            dns.publish_port_config(node_id, config_fqdn);
+            spdlog::info("DNS: published _config TXT for {} (host={})", node_id, config_fqdn);
         }
     }