Merge b640-601: honest deploy acks — Applied only after the address-space outcome, degraded flag + reason (#601)

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

# Conflicts:
#	src/Server/ZB.MOM.WW.OtOpcUa.Runtime/OpcUa/OpcUaPublishActor.cs

tests/Core/ZB.MOM.WW.OtOpcUa.Commons.Tests/MeshTransportDtoMapperTests.cs

@@ -201,6 +201,61 @@ public class MeshTransportDtoMapperTests
         back.FailureReason.ShouldBeEmpty();
     }
 
+    [Fact]
+    public void ApplyAck_Degraded_RoundTrips_WithItsReason()
+    {
+        // #601: an Applied ack whose address-space apply was DEGRADED must reach central as degraded —
+        // a node that loses the flag on the wire reports a clean apply it did not have.
+        var domain = new ApplyAck(
+            new DeploymentId(DeploymentGuid),
+            new NodeId("site-a-1"),
+            ApplyAckOutcome.Applied,
+            null,
+            new CorrelationId(CorrelationGuid),
+            Degraded: true,
+            DegradedReason: "failedNodes=3");
+
+        var back = MeshTransportDtoMapper.FromProto(Wire(MeshTransportDtoMapper.ToProto(domain)));
+
+        back.ShouldBe(domain);
+        back.Degraded.ShouldBeTrue();
+        back.DegradedReason.ShouldBe("failedNodes=3");
+    }
+
+    [Fact]
+    public void ApplyAck_Clean_EncodesNoDegradedFields()
+    {
+        var proto = MeshTransportDtoMapper.ToProto(new ApplyAck(
+            new DeploymentId(DeploymentGuid), new NodeId("site-a-1"), ApplyAckOutcome.Applied, null,
+            new CorrelationId(CorrelationGuid)));
+
+        proto.Degraded.ShouldBeFalse();
+        proto.HasDegradedReason.ShouldBeFalse();
+    }
+
+    [Fact]
+    public void ApplyAck_FromAnOldNode_WithoutTheDegradedFields_DecodesAsTodaysCleanAck()
+    {
+        // #601 compatibility: a node built before the degraded fields existed sends exactly fields 1-5.
+        // Its ack must decode exactly as it always did — not degraded, no reason.
+        var oldNodeBytes = new ApplyAckMessage
+        {
+            DeploymentId = DeploymentGuid.ToString("N"),
+            NodeId = "site-a-1",
+            Outcome = ApplyOutcome.Applied,
+            CorrelationId = CorrelationGuid.ToString("N"),
+        }.ToByteArray();
+
+        var back = MeshTransportDtoMapper.FromProto(ApplyAckMessage.Parser.ParseFrom(oldNodeBytes));
+
+        back.Outcome.ShouldBe(ApplyAckOutcome.Applied);
+        back.Degraded.ShouldBeFalse();
+        back.DegradedReason.ShouldBeNull();
+        back.ShouldBe(new ApplyAck(
+            new DeploymentId(DeploymentGuid), new NodeId("site-a-1"), ApplyAckOutcome.Applied, null,
+            new CorrelationId(CorrelationGuid)));
+    }
+
     [Fact]
     public void ApplyAck_UnspecifiedOutcome_Throws_RatherThanDecodingToAMeaningfulValue()
     {