Implement graceful worker shutdown

src/MxGateway.Worker.Tests/Sta/StaCommandDispatcherTests.cs

@@ -110,6 +110,27 @@ public sealed class StaCommandDispatcherTests
         Assert.Equal("correlation-1", reply.CorrelationId);
     }
 
+    [Fact]
+    public async Task RequestShutdown_RejectsQueuedCommandButLetsCurrentCommandFinish()
+    {
+        using StaRuntime runtime = CreateRuntime();
+        runtime.Start();
+        BlockingCommandExecutor executor = new();
+        StaCommandDispatcher dispatcher = new(runtime, executor);
+        Task<MxCommandReply> current = dispatcher.DispatchAsync(CreateCommand("current", MxCommandKind.Register));
+        Assert.True(executor.Started.Wait(TimeSpan.FromSeconds(2)));
+        Task<MxCommandReply> pending = dispatcher.DispatchAsync(CreateCommand("pending", MxCommandKind.AddItem));
+
+        dispatcher.RequestShutdown();
+        MxCommandReply pendingReply = await pending;
+        executor.Release();
+        MxCommandReply currentReply = await current;
+
+        Assert.Equal(ProtocolStatusCode.WorkerUnavailable, pendingReply.ProtocolStatus.Code);
+        Assert.Equal(ProtocolStatusCode.Ok, currentReply.ProtocolStatus.Code);
+        Assert.Equal(new[] { "current" }, executor.CorrelationIds);
+    }
+
     [Fact]
     public async Task PopulateHeartbeat_ReportsCurrentCorrelationAndPendingCount()
     {