Implement graceful worker shutdown

src/MxGateway.Worker.Tests/Ipc/WorkerPipeSessionTests.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Runtime.InteropServices;
@@ -147,6 +148,29 @@ public sealed class WorkerPipeSessionTests
         Assert.Equal(ProtocolStatusCode.WorkerUnavailable, written[1].WorkerFault.ProtocolStatus.Code);
     }
 
+    [Fact]
+    public async Task RunAsync_WithWorkerShutdown_WritesShutdownAckAndReturns()
+    {
+        WorkerFrameProtocolOptions options = CreateOptions();
+        MemoryStream inbound = new();
+        WorkerFrameWriter inboundWriter = new(inbound, options);
+        await inboundWriter.WriteAsync(CreateGatewayHelloEnvelope());
+        await inboundWriter.WriteAsync(CreateWorkerShutdownEnvelope());
+        inbound.Position = 0;
+        MemoryStream outbound = new();
+        WorkerPipeSession session = CreateSession(inbound, outbound, options);
+
+        await session.CompleteStartupHandshakeAsync(_ => Task.CompletedTask);
+        await session.RunAsync();
+
+        WorkerEnvelope[] written = ReadWrittenFrames(outbound, options);
+        Assert.Equal(3, written.Length);
+        Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerHello, written[0].BodyCase);
+        Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerReady, written[1].BodyCase);
+        Assert.Equal(WorkerEnvelope.BodyOneofCase.WorkerShutdownAck, written[2].BodyCase);
+        Assert.Equal(ProtocolStatusCode.Ok, written[2].WorkerShutdownAck.Status.Code);
+    }
+
     private static WorkerPipeSession CreateSession(
         Stream inbound,
         Stream outbound,
@@ -185,6 +209,21 @@ public sealed class WorkerPipeSessionTests
         };
     }
 
+    private static WorkerEnvelope CreateWorkerShutdownEnvelope()
+    {
+        return new WorkerEnvelope
+        {
+            ProtocolVersion = GatewayContractInfo.WorkerProtocolVersion,
+            SessionId = SessionId,
+            Sequence = 2,
+            WorkerShutdown = new WorkerShutdown
+            {
+                GracePeriod = Google.Protobuf.WellKnownTypes.Duration.FromTimeSpan(TimeSpan.FromSeconds(1)),
+                Reason = "test-shutdown",
+            },
+        };
+    }
+
     private static WorkerEnvelope[] ReadWrittenFrames(
         MemoryStream stream,
         WorkerFrameProtocolOptions options)