test(gateway): cover failback reason, FromFeed/SinceUtc badge paths; style + bounded drain (Tests-032..035)

src/ZB.MOM.WW.MxGateway.Tests/Alarms/AlarmFailoverEndToEndTests.cs

@@ -312,21 +312,35 @@ public sealed class AlarmFailoverEndToEndTests
             WaitTimeout);
 
         // New subscriber: its initial cache snapshot must carry the degraded flags.
+        // Bound the drain so a regression that never emits SnapshotComplete fails
+        // with a clean TimeoutException (via cancellation) instead of hanging.
         using CancellationTokenSource newStreamCts = new();
+        using CancellationTokenSource drainTimeoutCts = new();
+        drainTimeoutCts.CancelAfter(WaitTimeout);
+        using CancellationTokenSource linkedDrainCts =
+            CancellationTokenSource.CreateLinkedTokenSource(newStreamCts.Token, drainTimeoutCts.Token);
         ActiveAlarmSnapshot? initialActiveAlarm = null;
-        await foreach (AlarmFeedMessage message in monitor.StreamAsync(null, newStreamCts.Token))
+        try
         {
-            if (message.PayloadCase == AlarmFeedMessage.PayloadOneofCase.ActiveAlarm
-                && message.ActiveAlarm.AlarmFullReference == "Galaxy!Area.Tank02.Lo")
+            await foreach (AlarmFeedMessage message in monitor.StreamAsync(null, linkedDrainCts.Token))
             {
-                initialActiveAlarm = message.ActiveAlarm;
-            }
+                if (message.PayloadCase == AlarmFeedMessage.PayloadOneofCase.ActiveAlarm
+                    && message.ActiveAlarm.AlarmFullReference == "Galaxy!Area.Tank02.Lo")
+                {
+                    initialActiveAlarm = message.ActiveAlarm;
+                }
 
-            if (message.PayloadCase == AlarmFeedMessage.PayloadOneofCase.SnapshotComplete)
-            {
-                break;
+                if (message.PayloadCase == AlarmFeedMessage.PayloadOneofCase.SnapshotComplete)
+                {
+                    break;
+                }
             }
         }
+        catch (OperationCanceledException) when (drainTimeoutCts.IsCancellationRequested)
+        {
+            throw new TimeoutException(
+                "The new subscriber did not receive a SnapshotComplete message within the timeout.");
+        }
 
         Assert.NotNull(initialActiveAlarm);
         Assert.True(initialActiveAlarm!.Degraded);