worker(alarms): net48 index fix; enforce ProbeIntervalSeconds; OOM-safe catch; reset-on-failure test

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/FailoverAlarmConsumer.cs

@@ -63,6 +63,7 @@ public sealed class FailoverAlarmConsumer : IMxAccessAlarmConsumer
     private int consecutiveFailures;
     private int cleanProbes;
     private bool disposed;
+    private DateTime lastProbeAtUtc = DateTime.MinValue;
 
     /// <summary>
     ///     The subscription expression passed to <see cref="Subscribe"/>.
@@ -177,6 +178,16 @@ public sealed class FailoverAlarmConsumer : IMxAccessAlarmConsumer
     ///         drive it directly.
     ///     </para>
     ///     <para>
+    ///         <strong>Probe throttle.</strong> When
+    ///         <see cref="FailoverSettings.ProbeIntervalSeconds"/> is greater than
+    ///         zero, successive calls to this method are throttled: a probe is
+    ///         skipped unless at least that many seconds have elapsed since the
+    ///         last probe that was actually executed. When
+    ///         <see cref="FailoverSettings.ProbeIntervalSeconds"/> is zero, the
+    ///         throttle is disabled and every call probes immediately (the default
+    ///         used by unit tests).
+    ///     </para>
+    ///     <para>
     ///         <strong>Why PollOnce only — no re-Subscribe.</strong>
     ///         Failover does NOT tear down the primary's subscription;
     ///         <see cref="WnWrapAlarmConsumer"/> is single-subscribe and would
@@ -202,6 +213,16 @@ public sealed class FailoverAlarmConsumer : IMxAccessAlarmConsumer
         if (disposed) throw new ObjectDisposedException(nameof(FailoverAlarmConsumer));
         if (active != Active.Standby) return;
 
+        // Throttle probes to the configured cadence. When ProbeIntervalSeconds
+        // is 0 the throttle is disabled and every call probes immediately.
+        if (settings.ProbeIntervalSeconds > 0
+            && (DateTime.UtcNow - lastProbeAtUtc).TotalSeconds < settings.ProbeIntervalSeconds)
+        {
+            return;
+        }
+
+        lastProbeAtUtc = DateTime.UtcNow;
+
         try
         {
             // Re-poll the still-subscribed primary. Do NOT call Subscribe —
@@ -278,7 +299,7 @@ public sealed class FailoverAlarmConsumer : IMxAccessAlarmConsumer
         {
             action();
         }
-        catch (Exception ex)
+        catch (Exception ex) when (ex is not OutOfMemoryException)
         {
             consecutiveFailures++;
             int hresult = ex is COMException ? ex.HResult : 0;