Cluster discovery

Use the options overload to query live cluster information through Kafka's DescribeCluster RPC:

using Dekaf;
using Dekaf.Admin;

await using var admin = Kafka.CreateAdminClient()
    .WithBootstrapServers("localhost:9092")
    .Build();

var snapshot = await admin.DescribeClusterAsync(new DescribeClusterOptions
{
    IncludeFencedBrokers = true
});

foreach (var node in snapshot.Nodes)
{
    Console.WriteLine($"{node.NodeId}: {node.Host}:{node.Port}, fenced={node.IsFenced}");
}

Fenced brokers remain registered with the cluster but are unavailable for normal client traffic. This read-only discovery does not unregister nodes, change cluster state, or add fenced nodes to producer/consumer routing metadata.

IncludeFencedBrokers defaults to false. Requesting it requires DescribeCluster v2 on the actual destination broker. Dekaf throws BrokerVersionException when that capability is absent; it never silently drops the option.

ClusterDescriptionSnapshot.EndpointType distinguishes broker nodes from controller nodes. With WithBootstrapControllers(...), the options overload describes controllers and rejects IncludeFencedBrokers = true with NotSupportedException. Use broker bootstrap endpoints to discover fenced brokers. ClusterNodeDescription.IsFenced is nullable: controller nodes and responses older than v2 have no broker fencing status.

The existing DescribeClusterAsync(cancellationToken) overload retains its metadata-cache semantics and result type. The new overload always makes a live request and returns a separate administrative snapshot. Pass a cancellation token to bound initialization, retries, and the request.

Custom IAdminClient implementations remain compatible. They can opt into IClusterDiscoveryAdminClient; otherwise the extension method throws NotSupportedException.

Dekaf.Testing.InMemoryAdminClient implements this capability with its single in-memory broker. Both option values return that broker with IsFenced = false; the in-memory cluster does not simulate fencing. Discovery observes the configured admin fault plan and cancellation, and leaves routing metadata unchanged.