Surface historian plugin and alarm-tracking health in the status dashboard so operators can detect misconfiguration and runtime degradation that previously showed as fully healthy

Wraps the 4 HistoryRead overrides and OnAlarmAcknowledge with PerformanceMetrics.BeginOperation, adds alarm counters to LmxNodeManager, publishes a structured HistorianPluginOutcome from HistorianPluginLoader, and extends HealthCheckService with plugin-load, history-read, and alarm-ack-failure degradation rules.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.LmxOpcUa.Host/Historian/HistorianPluginLoader.cs

@@ -6,6 +6,39 @@ using ZB.MOM.WW.LmxOpcUa.Host.Configuration;
 
 namespace ZB.MOM.WW.LmxOpcUa.Host.Historian
 {
+    /// <summary>
+    ///     Result of the most recent historian plugin load attempt.
+    /// </summary>
+    public enum HistorianPluginStatus
+    {
+        /// <summary>Historian.Enabled is false; TryLoad was not called.</summary>
+        Disabled,
+        /// <summary>Plugin DLL was not present in the Historian/ subfolder.</summary>
+        NotFound,
+        /// <summary>Plugin file exists but could not be loaded or instantiated.</summary>
+        LoadFailed,
+        /// <summary>Plugin loaded and an IHistorianDataSource was constructed.</summary>
+        Loaded
+    }
+
+    /// <summary>
+    ///     Structured outcome of a <see cref="HistorianPluginLoader.TryLoad"/> or
+    ///     <see cref="HistorianPluginLoader.MarkDisabled"/> call, used by the status dashboard.
+    /// </summary>
+    public sealed class HistorianPluginOutcome
+    {
+        public HistorianPluginOutcome(HistorianPluginStatus status, string pluginPath, string? error)
+        {
+            Status = status;
+            PluginPath = pluginPath;
+            Error = error;
+        }
+
+        public HistorianPluginStatus Status { get; }
+        public string PluginPath { get; }
+        public string? Error { get; }
+    }
+
     /// <summary>
     ///     Loads the Wonderware historian plugin assembly from the Historian/ subfolder next to
     ///     the host executable. Used so the aahClientManaged SDK is not needed on hosts that run
@@ -23,9 +56,28 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.Historian
         private static bool _resolverInstalled;
         private static string? _resolvedProbeDirectory;
 
+        /// <summary>
+        ///     Gets the outcome of the most recent load attempt (or <see cref="HistorianPluginStatus.Disabled"/>
+        ///     if the loader has never been invoked). The dashboard reads this to distinguish "disabled",
+        ///     "plugin missing", and "plugin crashed".
+        /// </summary>
+        public static HistorianPluginOutcome LastOutcome { get; private set; }
+            = new HistorianPluginOutcome(HistorianPluginStatus.Disabled, string.Empty, null);
+
+        /// <summary>
+        ///     Records that the historian plugin is disabled by configuration. Called by
+        ///     <c>OpcUaService</c> when <c>Historian.Enabled=false</c> so the status dashboard can
+        ///     report the exact reason history is unavailable.
+        /// </summary>
+        public static void MarkDisabled()
+        {
+            LastOutcome = new HistorianPluginOutcome(HistorianPluginStatus.Disabled, string.Empty, null);
+        }
+
         /// <summary>
         ///     Attempts to load the historian plugin and construct an <see cref="IHistorianDataSource"/>.
-        ///     Returns null on any failure so the server can continue with history unsupported.
+        ///     Returns null on any failure so the server can continue with history unsupported. The
+        ///     specific reason is published on <see cref="LastOutcome"/>.
         /// </summary>
         public static IHistorianDataSource? TryLoad(HistorianConfiguration config)
         {
@@ -37,6 +89,7 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.Historian
                 Log.Warning(
                     "Historian plugin not found at {PluginPath} — history read operations will return BadHistoryOperationUnsupported",
                     pluginPath);
+                LastOutcome = new HistorianPluginOutcome(HistorianPluginStatus.NotFound, pluginPath, null);
                 return null;
             }
 
@@ -49,6 +102,9 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.Historian
                 if (entryType == null)
                 {
                     Log.Warning("Historian plugin {PluginPath} does not expose {EntryType}", pluginPath, PluginEntryType);
+                    LastOutcome = new HistorianPluginOutcome(
+                        HistorianPluginStatus.LoadFailed, pluginPath,
+                        $"Plugin assembly does not expose entry type {PluginEntryType}");
                     return null;
                 }
 
@@ -56,6 +112,9 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.Historian
                 if (create == null)
                 {
                     Log.Warning("Historian plugin entry type {EntryType} missing static {Method}", PluginEntryType, PluginEntryMethod);
+                    LastOutcome = new HistorianPluginOutcome(
+                        HistorianPluginStatus.LoadFailed, pluginPath,
+                        $"Plugin entry type {PluginEntryType} is missing a public static {PluginEntryMethod} method");
                     return null;
                 }
 
@@ -63,15 +122,22 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.Historian
                 if (result is IHistorianDataSource dataSource)
                 {
                     Log.Information("Historian plugin loaded from {PluginPath}", pluginPath);
+                    LastOutcome = new HistorianPluginOutcome(HistorianPluginStatus.Loaded, pluginPath, null);
                     return dataSource;
                 }
 
                 Log.Warning("Historian plugin {PluginPath} returned an object that does not implement IHistorianDataSource", pluginPath);
+                LastOutcome = new HistorianPluginOutcome(
+                    HistorianPluginStatus.LoadFailed, pluginPath,
+                    "Plugin entry method returned an object that does not implement IHistorianDataSource");
                 return null;
             }
             catch (Exception ex)
             {
                 Log.Warning(ex, "Failed to load historian plugin from {PluginPath} — history disabled", pluginPath);
+                LastOutcome = new HistorianPluginOutcome(
+                    HistorianPluginStatus.LoadFailed, pluginPath,
+                    ex.GetBaseException().Message);
                 return null;
             }
         }