Issue #14: implement event streaming and backpressure

src/MxGateway.Tests/Gateway/Grpc/MxAccessGatewayServiceTests.cs

@@ -184,6 +184,7 @@ public sealed class MxAccessGatewayServiceTests
             identityAccessor ?? new GatewayRequestIdentityAccessor(),
             new MxAccessGrpcRequestValidator(),
             new MxAccessGrpcMapper(),
+            new FakeEventStreamService(sessionManager),
             NullLogger<MxAccessGatewayService>.Instance);
     }
 
@@ -275,6 +276,11 @@ public sealed class MxAccessGatewayServiceTests
 
         public List<WorkerEvent> Events { get; } = [];
 
+        public void RecordReadEventsSessionId(string sessionId)
+        {
+            LastReadEventsSessionId = sessionId;
+        }
+
         public Task<GatewaySession> OpenSessionAsync(
             SessionOpenRequest request,
             string? clientIdentity,
@@ -343,6 +349,27 @@ public sealed class MxAccessGatewayServiceTests
         }
     }
 
+    private sealed class FakeEventStreamService(FakeSessionManager sessionManager) : IEventStreamService
+    {
+        public async IAsyncEnumerable<MxEvent> StreamEventsAsync(
+            StreamEventsRequest request,
+            [EnumeratorCancellation] CancellationToken cancellationToken)
+        {
+            sessionManager.RecordReadEventsSessionId(request.SessionId);
+            foreach (WorkerEvent workerEvent in sessionManager.Events)
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+                await Task.Yield();
+                if (workerEvent.Event.WorkerSequence <= request.AfterWorkerSequence)
+                {
+                    continue;
+                }
+
+                yield return workerEvent.Event;
+            }
+        }
+    }
+
     private sealed class FakeWorkerClient(int processId) : IWorkerClient
     {
         public string SessionId { get; } = "session-1";