Merge #597/#599: real UnshelveTime, commented re-ack reports, native ack refused off-Primary, /alerts ack-path test; surgically-added raw nodes announced, equipment-with-references removal keeps references severed; Backing* parity guard

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

src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/AlarmConditionSnapshot.cs

@@ -24,6 +24,12 @@ namespace ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
 ///     Carries the full sub-code since #519, so a comms-lost condition reports
 ///     <see cref="OpcUaStatus.BadNoCommunication"/> rather than a bare <see cref="OpcUaStatus.Bad"/>.
 /// </param>
+/// <param name="UnshelveAtUtc">
+///     For <see cref="AlarmShelvingKind.Timed"/>, the UTC instant the engine expires the shelve; otherwise
+///     <c>null</c>. Carried so the node's Part 9 <c>ShelvingState.UnshelveTime</c> reports the real remaining
+///     time instead of the SDK's ~24.8-day ceiling (Gitea #597). A timed snapshot without it (a caller that
+///     predates the field) falls back to that ceiling — the engine still owns the expiry either way.
+/// </param>
 public sealed record AlarmConditionSnapshot(
     bool Active,
     bool Acknowledged,
@@ -32,7 +38,8 @@ public sealed record AlarmConditionSnapshot(
     AlarmShelvingKind Shelving,
     ushort Severity,
     string Message,
-    uint StatusCode = OpcUaStatus.Good);
+    uint StatusCode = OpcUaStatus.Good,
+    DateTime? UnshelveAtUtc = null);
 
 /// <summary>
 ///     Commons-local mirror of the Core <c>ShelvingKind</c> enum so this assembly carries no