gRPC M0 R0.2: tag metadata over gRPC (GetTagInfosFromName, live-verified)

Routes HistorianClient.GetTagMetadataAsync over gRPC when Transport==RemoteGrpc,
via the new Grpc/HistorianGrpcTagClient calling RetrievalService.GetTagInfosFromName
(the plural string-handle metadata op).

- String handle = the Open2 storage-session GUID formatted uppercase (the format
  that resolves the native string-handle path); threaded out of the shared handshake
  via a new HistorianGrpcHandshake.Session { ClientHandle, StorageSessionId, StringHandle }.
- Request btTagNames = uint count + per-name(uint charCount + UTF-16LE) — golden-byte
  unit-tested (BuildTagNamesBuffer).
- Response btTagInfos = uint count + CTagMetadata records — decoded by the existing
  HistorianTagQueryProtocol.ParseGetTagInfoResponse; data type via the shared MapDataType.

The 2020 WCF string-handle wall does NOT apply on the gRPC front door, as the
string-handle-wall RE note predicted. LIVE-VERIFIED against a real 2023 R2 server:
GetTagMetadataAsync returns the requested tag with a valid decoded data type.

216 unit tests pass. Captured framing confirmed live then discarded; no tag names
or identities committed.

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

src/AVEVA.Historian.Client/Grpc/HistorianGrpcHandshake.cs

@@ -20,10 +20,30 @@ namespace AVEVA.Historian.Client.Grpc;
 /// </summary>
 internal static class HistorianGrpcHandshake
 {
+    /// <summary>
+    /// The handles produced by a successful OpenConnection. <see cref="ClientHandle"/> is the
+    /// transient <c>uint</c> session token used by StartQuery/GetSystemParameter and the other
+    /// uint-handle ops. <see cref="StorageSessionId"/> is the storage-session GUID used (formatted
+    /// uppercase via <see cref="StringHandle"/>) by the string-handle ops
+    /// (GetTagInfosFromName, GetTagExtendedPropertiesFromName, ExecuteSqlCommand, ...).
+    /// </summary>
+    internal readonly record struct Session(uint ClientHandle, Guid StorageSessionId)
+    {
+        /// <summary>The storage GUID in the uppercase "D" form the native string-handle ops require.</summary>
+        public string StringHandle => StorageSessionId.ToString("D").ToUpperInvariant();
+    }
+
+    /// <summary>Convenience overload for callers that only need the uint client handle.</summary>
     public static uint OpenAuthenticatedConnection(
         HistorianGrpcConnection connection,
         HistorianClientOptions options,
         CancellationToken cancellationToken)
+        => OpenSession(connection, options, cancellationToken).ClientHandle;
+
+    public static Session OpenSession(
+        HistorianGrpcConnection connection,
+        HistorianClientOptions options,
+        CancellationToken cancellationToken)
     {
         DateTime Deadline() => DateTime.UtcNow.Add(options.RequestTimeout);
 
@@ -68,7 +88,7 @@ internal static class HistorianGrpcHandshake
             throw new InvalidOperationException($"gRPC OpenConnection failed (errorLen={err.Length}, responseLen={open2Response.Length}).");
         }
 
-        (uint clientHandle, _) = HistorianNativeHandshake.ParseOpenConnectionResponse(open2Response);
-        return clientHandle;
+        (uint clientHandle, Guid storageSessionId) = HistorianNativeHandshake.ParseOpenConnectionResponse(open2Response);
+        return new Session(clientHandle, storageSessionId);
     }
 }