Preserve framed reads across fake worker emission gates

src/ZB.MOM.WW.MxGateway.Tests/Gateway/GatewayEndToEndMultiSubscriberTests.cs

@@ -685,19 +685,19 @@ public sealed class GatewayEndToEndMultiSubscriberTests
             int advisedItemHandle = 0;
             int emittedCount = 0;
 
-            // Read envelopes one at a time. Between each envelope, if we have a
-            // subscription and the gate is ready, emit an event before reading the
-            // next envelope. When _stopEmitting is set, drain the gate and read
-            // remaining envelopes (including shutdown) without emitting.
+            await using GatedWorkerEnvelopeReader incoming = new(
+                harness.ReadGatewayEnvelopeAsync, _emitGate, cancellationToken);
             while (!cancellationToken.IsCancellationRequested)
             {
-                // While subscribed and not stopped, try to emit gated events using
-                // a short-timeout peek at the gate — yield to incoming envelopes to
-                // avoid starving shutdown processing.
-                while (advisedServerHandle != 0
-                    && !_stopEmitting
-                    && await _emitGate.WaitAsync(millisecondsTimeout: 0).ConfigureAwait(false))
+                WorkerEnvelope? envelope = await incoming.ReadOrGateAsync(
+                    advisedServerHandle != 0 && !_stopEmitting).ConfigureAwait(false);
+                if (envelope is null)
                 {
+                    if (_stopEmitting)
+                    {
+                        continue;
+                    }
+
                     int index = ++emittedCount;
                     await harness.EmitEventAsync(
                         MxEventFamily.OnDataChange,
@@ -714,20 +714,6 @@ public sealed class GatewayEndToEndMultiSubscriberTests
                             };
                             mxEvent.OnDataChange = new OnDataChangeEvent();
                         }).ConfigureAwait(false);
-                }
-
-                // Use a short timeout so the emit loop above is re-evaluated
-                // periodically — but long enough not to spam.
-                WorkerEnvelope? envelope = null;
-                try
-                {
-                    using CancellationTokenSource readCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
-                    readCts.CancelAfter(TimeSpan.FromMilliseconds(50));
-                    envelope = await harness.ReadGatewayEnvelopeAsync(readCts.Token).ConfigureAwait(false);
-                }
-                catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
-                {
-                    // Timed out waiting for an envelope — loop back to check gate / emit.
                     continue;
                 }