feat: execute full-repo remaining parity closure plan

src/NATS.Server/Routes/RouteCompressionCodec.cs

@@ -0,0 +1,26 @@
+using System.IO.Compression;
+
+namespace NATS.Server.Routes;
+
+public static class RouteCompressionCodec
+{
+    public static byte[] Compress(ReadOnlySpan<byte> payload)
+    {
+        using var output = new MemoryStream();
+        using (var stream = new DeflateStream(output, CompressionLevel.Fastest, leaveOpen: true))
+        {
+            stream.Write(payload);
+        }
+
+        return output.ToArray();
+    }
+
+    public static byte[] Decompress(ReadOnlySpan<byte> payload)
+    {
+        using var input = new MemoryStream(payload.ToArray());
+        using var stream = new DeflateStream(input, CompressionMode.Decompress);
+        using var output = new MemoryStream();
+        stream.CopyTo(output);
+        return output.ToArray();
+    }
+}

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);

src/NATS.Server/Routes/RouteManager.cs

@@ -25,6 +25,14 @@ public sealed class RouteManager : IAsyncDisposable
 
     public string ListenEndpoint => $"{_options.Host}:{_options.Port}";
 
+    public RouteTopologySnapshot BuildTopologySnapshot()
+    {
+        return new RouteTopologySnapshot(
+            _serverId,
+            _routes.Count,
+            _connectedServerIds.Keys.OrderBy(static k => k, StringComparer.Ordinal).ToArray());
+    }
+
     public RouteManager(
         ClusterOptions options,
         ServerStats stats,
@@ -254,3 +262,8 @@ public sealed class RouteManager : IAsyncDisposable
 
     public int RouteCount => _routes.Count;
 }
+
+public sealed record RouteTopologySnapshot(
+    string ServerId,
+    int RouteCount,
+    IReadOnlyList<string> ConnectedServerIds);