test(redundancy): lock in stale-Terminated guard + clarify OnTerminated (code-review)

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Health/PeerProbeSupervisor.cs

@@ -108,12 +108,15 @@ public sealed class PeerProbeSupervisor : ReceiveActor
     /// <param name="t">The termination notice for the dead child.</param>
     private void OnTerminated(Terminated t)
     {
-        var dead = _children.FirstOrDefault(kvp => kvp.Value.Equals(t.ActorRef));
-        if (!dead.Equals(default(KeyValuePair<NodeId, IActorRef>)) && dead.Value is not null)
-        {
-            _children.Remove(dead.Key);
-            _log.Debug("PeerProbeSupervisor: pruned terminated child for peer {Peer}", dead.Key);
-        }
+        var entry = _children.FirstOrDefault(kvp => kvp.Value.Equals(t.ActorRef));
+        // No-match yields Value == null because IActorRef is a reference type. A null here means the
+        // terminated ref isn't our CURRENT child for any peer — either it was already pruned in
+        // OnSnapshot (deliberate stop pre-removes from _children), or it's a stale old-generation
+        // child whose peer has since been re-spawned with a fresh child. Either way: no-op, so we
+        // never evict the fresh same-peer child on a stale Terminated.
+        if (entry.Value is null) return;
+        _children.Remove(entry.Key);
+        _log.Debug("PeerProbeSupervisor: pruned terminated child for peer {Peer}", entry.Key);
     }
 
     /// <summary>