refactor(alarms): harden ExtractTagAlarm severity parse (TryGetInt32) + trim projector prior-state (review nits)

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/NativeAlarmProjector.cs

@@ -12,8 +12,7 @@ namespace ZB.MOM.WW.OtOpcUa.Runtime.Drivers;
 /// </summary>
 public sealed class NativeAlarmProjector
 {
-    private readonly Dictionary<string, (bool Active, bool Acked, ushort Severity, string Message)> _prior =
-        new(StringComparer.Ordinal);
+    private readonly Dictionary<string, (bool Active, bool Acked)> _prior = new(StringComparer.Ordinal);
 
     /// <summary>Project an alarm transition onto the full condition snapshot for <paramref name="nodeId"/>.</summary>
     /// <param name="nodeId">The materialised condition node's id (the projection's state key).</param>
@@ -21,9 +20,7 @@ public sealed class NativeAlarmProjector
     /// <returns>The full Part 9 condition snapshot to write to the node.</returns>
     public AlarmConditionSnapshot Project(string nodeId, AlarmEventArgs e)
     {
-        var prev = _prior.TryGetValue(nodeId, out var p)
-            ? p
-            : (Active: false, Acked: true, Severity: (ushort)0, Message: string.Empty);
+        var prev = _prior.TryGetValue(nodeId, out var p) ? p : (Active: false, Acked: true);
         var sev = MapSeverity(e.Severity);
         var (active, acked) = e.Kind switch
         {
@@ -32,7 +29,7 @@ public sealed class NativeAlarmProjector
             AlarmTransitionKind.Clear => (false, prev.Acked),
             _ => (prev.Active, prev.Acked),
         };
-        _prior[nodeId] = (active, acked, sev, e.Message);
+        _prior[nodeId] = (active, acked);
         return new AlarmConditionSnapshot(
             Active: active, Acknowledged: acked, Confirmed: true, Enabled: true,
             Shelving: AlarmShelvingKind.Unshelved, Severity: sev, Message: e.Message);