perf(worker): signal-driven event drain — removes the 25 ms latency floor and idle wakeups

src/ZB.MOM.WW.MxGateway.Worker/Ipc/WorkerPipeSession.cs

@@ -15,6 +15,11 @@ namespace ZB.MOM.WW.MxGateway.Worker.Ipc;
 
 public sealed class WorkerPipeSession
 {
+    // Fallback ceiling for the event drain loop's wait — not a poll period. MxAccessEventQueue
+    // signals on enqueue (and on a recorded fault), so the loop wakes as soon as there is something
+    // to ship instead of paying up to this interval of latency on every burst from idle, and an
+    // idle worker parks instead of waking 40x/s. The interval survives only as the bound on how
+    // long the loop may sleep unsignalled, which keeps its DrainFault() poll on a known cadence.
     private static readonly TimeSpan EventDrainInterval = TimeSpan.FromMilliseconds(25);
     private static readonly TimeSpan BackgroundTaskStopTimeout = TimeSpan.FromSeconds(1);
     private const uint EventDrainBatchSize = 128;
@@ -367,7 +372,15 @@ public sealed class WorkerPipeSession
             IReadOnlyList<WorkerEvent> events = runtimeSession.DrainEvents(EventDrainBatchSize);
             if (events.Count == 0)
             {
-                await Task.Delay(EventDrainInterval, cancellationToken).ConfigureAwait(false);
+                // Wait on the queue's wake signal rather than sleeping a fixed tick: an event
+                // enqueued by the STA completes this immediately, so the first event of a burst is
+                // framed at signal latency instead of waiting out EventDrainInterval, and a session
+                // with no traffic stops waking at all. The wait's outcome is intentionally ignored —
+                // whether a signal or the fallback ended it, the next pass re-checks DrainFault()
+                // and re-drains, which is also why one coalesced wake for many enqueues is safe.
+                await runtimeSession
+                    .WaitForEventsAsync(EventDrainInterval, cancellationToken)
+                    .ConfigureAwait(false);
                 continue;
             }