Node-specific feature discovery

Use DescribeFeaturesOptions.NodeId to inspect an individual node during a rolling upgrade:

using Dekaf.Admin;

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

var features = await admin.DescribeFeaturesAsync(new DescribeFeaturesOptions
{
    NodeId = 2,
    TimeoutMs = 10_000
});

foreach (var feature in features.SupportedFeatures)
{
    Console.WriteLine($"{feature.Key}: {feature.Value.MinVersion}..{feature.Value.MaxVersion}");
}

SupportedFeatures contains the ranges advertised by the selected connection. FinalizedFeatures and FinalizedFeaturesEpoch describe cluster-wide finalized levels; querying an older node does not replace a newer finalized epoch already observed by this client.

With broker bootstrap endpoints, NodeId must identify a broker in discovered metadata. With WithBootstrapControllers, it must identify a controller in discovered controller metadata. An explicit selection never falls back to another node. Unknown IDs, endpoint or identity mismatches, and connection failures produce errors. Version negotiation uses the selected connection, so different nodes can return different supported ranges.

Omit NodeId to select an arbitrary broker or the active controller. The original DescribeFeaturesAsync(CancellationToken) overload remains available. On the options overload, TimeoutMs bounds initialization, connection establishment, retries, and the query; it defaults to the client's request timeout. Negative values are invalid and zero times out immediately. Expiration throws TimeoutException; caller cancellation throws OperationCanceledException.

The built-in admin client exposes this additive operation through INodeFeatureAdminClient and an IAdminClient extension method. Existing custom implementations remain compatible; they must implement the optional capability to support the options overload. Unsupported implementations throw NotSupportedException.