Implement graceful worker shutdown

src/MxGateway.Tests/Gateway/Sessions/SessionManagerTests.cs

@@ -86,6 +86,26 @@ public sealed class SessionManagerTests
         Assert.Equal(0, metrics.GetSnapshot().OpenSessions);
     }
 
+    [Fact]
+    public async Task CloseSessionAsync_WhenWorkerShutdownFails_KillsWorker()
+    {
+        FakeWorkerClient workerClient = new()
+        {
+            ShutdownException = new WorkerClientException(
+                WorkerClientErrorCode.ShutdownTimeout,
+                "Worker shutdown timed out."),
+        };
+        SessionManager manager = CreateManager(new FakeSessionWorkerClientFactory(workerClient));
+        GatewaySession session = await manager.OpenSessionAsync(CreateOpenRequest(), "client-1", CancellationToken.None);
+
+        SessionManagerException exception = await Assert.ThrowsAsync<SessionManagerException>(
+            async () => await manager.CloseSessionAsync(session.SessionId, CancellationToken.None));
+
+        Assert.Equal(SessionManagerErrorCode.CloseFailed, exception.ErrorCode);
+        Assert.Equal(1, workerClient.ShutdownCount);
+        Assert.Equal(1, workerClient.KillCount);
+    }
+
     [Fact]
     public async Task OpenSessionAsync_WhenWorkerCreationFails_RemovesSessionFromRegistry()
     {
@@ -266,6 +286,8 @@ public sealed class SessionManagerTests
 
         public int KillCount { get; private set; }
 
+        public Exception? ShutdownException { get; init; }
+
         public Task StartAsync(CancellationToken cancellationToken)
         {
             return Task.CompletedTask;
@@ -302,6 +324,11 @@ public sealed class SessionManagerTests
             CancellationToken cancellationToken)
         {
             ShutdownCount++;
+            if (ShutdownException is not null)
+            {
+                throw ShutdownException;
+            }
+
             State = WorkerClientState.Closed;
             return Task.CompletedTask;
         }