feat(historian-gateway): GetHealthSnapshot via Probe/GetConnectionStatus (counter discipline)

Claude-Session: https://claude.ai/code/session_012SDSQ3AcaXqPcBtDESBRii

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway/GatewayHistorianDataSource.cs

@@ -23,6 +23,13 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway;
 /// </remarks>
 public sealed class GatewayHistorianDataSource : IHistorianDataSource, IAsyncDisposable
 {
+    /// <summary>
+    ///     <see cref="ConnectionStatus.ConnectionKind"/> is a combinable [Flags] value: the
+    ///     process-data connection is bit 0 (value 1), the event connection is bit 1 (value 2).
+    /// </summary>
+    private const uint ProcessConnectionFlag = 1;
+    private const uint EventConnectionFlag = 2;
+
     private readonly IHistorianGatewayClient _client;
     private readonly ILogger<GatewayHistorianDataSource> _logger;
 
@@ -34,6 +41,8 @@ public sealed class GatewayHistorianDataSource : IHistorianDataSource, IAsyncDis
     private long _totalSuccesses;
     private long _totalFailures;
     private int _consecutiveFailures;
+    private bool _processConnectionOpen;
+    private bool _eventConnectionOpen;
 
     /// <summary>Creates a gateway-backed historian data source.</summary>
     /// <param name="client">The gateway client seam used for all reads.</param>
@@ -162,17 +171,55 @@ public sealed class GatewayHistorianDataSource : IHistorianDataSource, IAsyncDis
                 LastSuccessTime: _lastSuccessUtc,
                 LastFailureTime: _lastFailureUtc,
                 LastError: _lastError,
-                // Connection-state caching arrives in T8 (RefreshConnectionStateAsync); until then
-                // both flags read closed. The gateway is non-clustered to us, so node fields are
-                // null/empty (mirrors the Wonderware client's Finding 010 posture).
-                ProcessConnectionOpen: false,
-                EventConnectionOpen: false,
+                // Cached connection flags last observed by RefreshConnectionStateAsync. The gateway
+                // is non-clustered to us, so node fields are null/empty (mirrors the Wonderware
+                // client's Finding 010 posture).
+                ProcessConnectionOpen: _processConnectionOpen,
+                EventConnectionOpen: _eventConnectionOpen,
                 ActiveProcessNode: null,
                 ActiveEventNode: null,
                 Nodes: []);
         }
     }
 
+    /// <summary>
+    ///     Refreshes the cached process / event connection flags by querying the gateway's
+    ///     connection status. Intended to be driven by a periodic health hosted-service, keeping
+    ///     <see cref="GetHealthSnapshot"/> pure observation (it never performs I/O). The flags are
+    ///     derived from <see cref="ConnectionStatus.ConnectedToServer"/> AND the matching
+    ///     <see cref="ConnectionStatus.ConnectionKind"/> flag bit. A failed status query is a health
+    ///     probe — it never throws to the caller; both flags degrade to closed until the next
+    ///     successful refresh.
+    /// </summary>
+    /// <param name="cancellationToken">A token to cancel the status query.</param>
+    /// <returns>A task that completes when the cached flags have been updated.</returns>
+    public async Task RefreshConnectionStateAsync(CancellationToken cancellationToken)
+    {
+        bool processOpen;
+        bool eventOpen;
+        try
+        {
+            var status = await _client.GetConnectionStatusAsync(cancellationToken).ConfigureAwait(false);
+            var connected = status.ConnectedToServer;
+            processOpen = connected && (status.ConnectionKind & ProcessConnectionFlag) != 0;
+            eventOpen = connected && (status.ConnectionKind & EventConnectionFlag) != 0;
+        }
+        catch (Exception)
+        {
+            // A health probe must never crash the host; an unreachable gateway degrades both
+            // connection flags to closed until the next successful refresh.
+            _logger.LogDebug("Historian gateway connection-status refresh failed; treating both connections as closed.");
+            processOpen = false;
+            eventOpen = false;
+        }
+
+        lock (_healthLock)
+        {
+            _processConnectionOpen = processOpen;
+            _eventConnectionOpen = eventOpen;
+        }
+    }
+
     /// <summary>
     ///     Reconciles a gateway at-time reply against the requested timestamps to honour the
     ///     <see cref="IHistorianDataSource.ReadAtTimeAsync"/> contract: exactly one snapshot per