R1.2 GetRuntimeParameter + string-handle wall RESOLVED (handle-format bug)

Execute HCAL roadmap R1.2 (GetRuntimeParameterAsync) end-to-end, and in doing so
discover that the "string-handle wall" blocking R1.1/R1.4/R1.5/R1.6 was a handle
FORMAT bug, not a missing native session/filter registration.

R1.2 (shipped, live-verified):
- Captured native GetRuntimeParameter -> WCF op aa/Stat/GETRP (string-handle op,
  GETHI's shape), via scripts/Capture-RuntimeParam.ps1 + instrument-wcf-{write,read}message.
- HistorianRuntimeParameterProtocol serializes pRequestBuff (54 67 01 00 + uint
  nameCount + per-name uint charCount + UTF-16) and parses pResponseBuff (version +
  uint resultCount + CRetVariant 0x43 VT_BSTR + uint16 len + uint16 charCount + UTF-16).
- IStatusServiceContract2.GetRuntimeParameter (GETRP) op; HistorianWcfStatusClient
  passes the Open2 storage-session GUID as the string handle, UPPERCASE.
- Public HistorianClient.GetRuntimeParameterAsync(name) via the dialect.
- Golden WcfRuntimeParameterProtocolTests + gated live test; returns HistorianVersion.

String-handle wall RESOLVED (proven, public APIs deferred):
- The Open2 storage GUID works as the string handle when sent UPPERCASE
  (ToString("D").ToUpperInvariant()); earlier "blocked" probes used lowercase.
- Live-probed GETHI (R1.4) -> returns data; ExeC (R1.1) -> Retr.GetV prime -> ExeC ->
  GetR returns a BinaryFormatter-serialized .NET DataTable. Gated
  StringHandleProbeDiagnosticTests + scripts/Capture-ExecSql.ps1 + exec-sql harness scenario.
- Docs flipped: wcf-string-handle-wall.md RESOLVED banner; roadmap R1.1/R1.4 reachable,
  R1.5/R1.6 likely; wcf-status-localhost.md GETRP section.
- R1.1/R1.4 public APIs NOT shipped: ExeC needs a GetR paging loop + a BinaryFormatter-
  stream parser (BinaryFormatter is removed from .NET 10); GETHI full-info struct needs
  its own capture.

223 unit tests pass; gated live tests green against the local 2020 Historian.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B6mcaT2PjRFKcogzp9UkfC

src/AVEVA.Historian.Client/Wcf/HistorianWcfStatusClient.cs

@@ -17,6 +17,19 @@ internal static class HistorianWcfStatusClient
         return Task.Run(() => GetSystemParameter(options, parameterName), cancellationToken);
     }
 
+    /// <summary>Diagnostic: the GETRP return code / error description from the last
+    /// <see cref="GetRuntimeParameterAsync"/> call (set only when the server rejects it).</summary>
+    public static string? LastRuntimeParameterError { get; private set; }
+
+    public static Task<string?> GetRuntimeParameterAsync(
+        HistorianClientOptions options,
+        string parameterName,
+        CancellationToken cancellationToken)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(parameterName);
+        return Task.Run(() => GetRuntimeParameter(options, parameterName), cancellationToken);
+    }
+
     public static Task<HistorianConnectionStatus> GetConnectionStatusAsync(
         HistorianClientOptions options,
         CancellationToken cancellationToken)
@@ -45,6 +58,49 @@ internal static class HistorianWcfStatusClient
         return value;
     }
 
+    private static string? GetRuntimeParameter(HistorianClientOptions options, string parameterName)
+    {
+        Guid contextKey = Guid.NewGuid();
+        var (histBinding, histEndpoint, _, _) = HistorianWcfBindingFactory.CreateBindingPair(options);
+        Binding statusBinding = HistorianWcfBindingFactory.CreateAuxiliaryBinding(options);
+        EndpointAddress statusEndpoint = HistorianWcfBindingFactory.CreateAuxiliaryEndpointAddress(options, HistorianWcfServiceNames.Status);
+
+        string? value = null;
+        LastRuntimeParameterError = null;
+        HistorianWcfAuthChainHelper.OpenAuthenticatedConnection(
+            options, histBinding, histEndpoint, contextKey, CancellationToken.None,
+            additionalSetup: (_, context) => value = QueryRuntimeParameter(statusBinding, statusEndpoint, context.StorageSessionId, parameterName));
+        return value;
+    }
+
+    private static string? QueryRuntimeParameter(Binding statusBinding, EndpointAddress statusEndpoint, Guid storageSessionId, string parameterName)
+    {
+        // GETRP takes the storage-session GUID as a string handle, formatted exactly as the
+        // native client sends it: uppercase, dash-separated, no braces.
+        string handle = storageSessionId.ToString("D").ToUpperInvariant();
+        byte[] requestBuffer = HistorianRuntimeParameterProtocol.SerializeRequest(parameterName);
+
+        ChannelFactory<IStatusServiceContract2> factory = new(statusBinding, statusEndpoint);
+        IStatusServiceContract2 channel = factory.CreateChannel();
+        ICommunicationObject co = (ICommunicationObject)channel;
+        try
+        {
+            bool ok = channel.GetRuntimeParameter(handle, requestBuffer, out byte[] responseBuffer, out byte[] errorBuffer);
+            if (!ok)
+            {
+                LastRuntimeParameterError = $"GETRP returned false (responseLen={responseBuffer?.Length ?? 0}, errorLen={errorBuffer?.Length ?? 0}).";
+                return null;
+            }
+
+            return HistorianRuntimeParameterProtocol.ParseSingleStringResult(responseBuffer ?? []);
+        }
+        finally
+        {
+            try { if (co.State == CommunicationState.Faulted) co.Abort(); else co.Close(); } catch { try { co.Abort(); } catch { } }
+            try { if (factory.State == CommunicationState.Faulted) factory.Abort(); else factory.Close(); } catch { try { factory.Abort(); } catch { } }
+        }
+    }
+
     private static string? QuerySystemParameter(Binding statusBinding, EndpointAddress statusEndpoint, uint clientHandle, string parameterName)
     {
         ChannelFactory<IStatusServiceContract2> factory = new(statusBinding, statusEndpoint);