feat: integrate jetstream meta-group placement

tests/NATS.Server.Tests/JetStreamMetaGroupTests.cs

@@ -0,0 +1,54 @@
+using NATS.Server.JetStream;
+using NATS.Server.JetStream.Cluster;
+using NATS.Server.JetStream.Models;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamMetaGroupTests
+{
+    [Fact]
+    public async Task Stream_create_requires_meta_group_commit()
+    {
+        await using var fixture = await JetStreamClusterFixture.StartAsync(nodes: 3);
+
+        var result = await fixture.CreateStreamAsync("ORDERS", replicas: 3);
+        result.Error.ShouldBeNull();
+
+        var meta = await fixture.GetMetaStateAsync();
+        meta.Streams.ShouldContain("ORDERS");
+    }
+}
+
+internal sealed class JetStreamClusterFixture : IAsyncDisposable
+{
+    private readonly JetStreamMetaGroup _metaGroup;
+    private readonly StreamManager _streamManager;
+
+    private JetStreamClusterFixture(JetStreamMetaGroup metaGroup, StreamManager streamManager)
+    {
+        _metaGroup = metaGroup;
+        _streamManager = streamManager;
+    }
+
+    public static Task<JetStreamClusterFixture> StartAsync(int nodes)
+    {
+        var meta = new JetStreamMetaGroup(nodes);
+        var streamManager = new StreamManager(meta);
+        return Task.FromResult(new JetStreamClusterFixture(meta, streamManager));
+    }
+
+    public Task<NATS.Server.JetStream.Api.JetStreamApiResponse> CreateStreamAsync(string name, int replicas)
+    {
+        var response = _streamManager.CreateOrUpdate(new StreamConfig
+        {
+            Name = name,
+            Subjects = [name.ToLowerInvariant() + ".*"],
+            Replicas = replicas,
+        });
+        return Task.FromResult(response);
+    }
+
+    public Task<MetaGroupState> GetMetaStateAsync() => Task.FromResult(_metaGroup.GetState());
+
+    public ValueTask DisposeAsync() => ValueTask.CompletedTask;
+}