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/HistorianClient.cs

@@ -154,6 +154,18 @@ public sealed class HistorianClient : IAsyncDisposable
         return _protocol.GetSystemParameterAsync(name, cancellationToken);
     }
 
+    /// <summary>
+    /// Reads a named Historian <em>runtime</em> parameter (the live server state surface,
+    /// distinct from the configuration <see cref="GetSystemParameterAsync"/>). Returns the
+    /// string value, or null when the server reports no value. Single string-valued parameters
+    /// only (the evidence-backed surface); see <c>HistorianRuntimeParameterProtocol</c>.
+    /// </summary>
+    public Task<string?> GetRuntimeParameterAsync(string name, CancellationToken cancellationToken = default)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(name);
+        return _protocol.GetRuntimeParameterAsync(name, cancellationToken);
+    }
+
     /// <summary>
     /// Creates or updates the named tag in the Historian Runtime database via
     /// <c>EnsureTags2</c>. Currently only <see cref="HistorianDataType.Float"/> is