Merge fix/c3-session-lifecycle: GWC-32 WorkerClient dispose is terminal, GWC-34 attach-after-dispose throws SessionNotReady, GWC-37 subtag watch-list coverage graded on provider status + re-resolved at failover edge

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardAlarmProviderStatus.cs

@@ -30,6 +30,14 @@ public sealed record DashboardAlarmProviderStatus(
     /// </summary>
     public const string ForcedSubtagLabel = "Subtag monitoring (forced)";
 
+    /// <summary>
+    ///     Badge label shown when the alarm manager is serving normally but the subtag standby
+    ///     behind it covers nothing — an empty or undiscoverable watch-list (GWC-37). The feed is
+    ///     healthy today; what is degraded is the fallback that would take over tomorrow, so the
+    ///     badge names the standby rather than claiming the feed has failed over.
+    /// </summary>
+    public const string NoSubtagStandbyLabel = "Alarm Manager (no subtag standby)";
+
     private const string HealthyBadge = "bg-success";
     private const string DegradedBadge = "bg-warning text-dark";
 
@@ -69,8 +77,18 @@ public sealed record DashboardAlarmProviderStatus(
             && status.Mode == AlarmProviderMode.Subtag
             && string.Equals(reason, AlarmProviderReasons.ForcedSubtag, StringComparison.Ordinal);
 
-        string label = !degraded ? AlarmManagerLabel : forced ? ForcedSubtagLabel : DegradedLabel;
-        string badge = !degraded ? HealthyBadge : forced ? ForcedSubtagBadge : DegradedBadge;
+        // GWC-37: degraded WITHOUT subtag mode means the alarm manager is still serving and the
+        // standby is the unsound half. "Subtag monitoring (degraded)" would misreport which
+        // provider is live, so this state gets its own label; the amber badge is shared because
+        // the operator action — fix discovery — is equally overdue in both.
+        bool standbyOnlyWarning = degraded && status.Mode != AlarmProviderMode.Subtag;
+
+        string label = !degraded
+            ? AlarmManagerLabel
+            : standbyOnlyWarning ? NoSubtagStandbyLabel : forced ? ForcedSubtagLabel : DegradedLabel;
+        string badge = !degraded
+            ? HealthyBadge
+            : standbyOnlyWarning ? DegradedBadge : forced ? ForcedSubtagBadge : DegradedBadge;
 
         return new DashboardAlarmProviderStatus(
             Mode: status.Mode,