feat: execute full-repo remaining parity closure plan

src/NATS.Server/Routes/RouteConnection.cs

@@ -1,5 +1,6 @@
 using System.Net.Sockets;
 using System.Text;
+using System.Text.Json;
 using NATS.Server.Subscriptions;
 
 namespace NATS.Server.Routes;
@@ -252,6 +253,17 @@ public sealed class RouteConnection(Socket socket) : IAsyncDisposable
         => token.Contains('.', StringComparison.Ordinal)
             || token.Contains('*', StringComparison.Ordinal)
             || token.Contains('>', StringComparison.Ordinal);
+
+    public static string BuildConnectInfoJson(string serverId, IEnumerable<string>? accounts, string? topologySnapshot)
+    {
+        var payload = new
+        {
+            server_id = serverId,
+            accounts = (accounts ?? []).ToArray(),
+            topology = topologySnapshot ?? string.Empty,
+        };
+        return JsonSerializer.Serialize(payload);
+    }
 }
 
 public sealed record RouteMessage(string Subject, string? ReplyTo, ReadOnlyMemory<byte> Payload);