feat(grpc): …OnSession seams on HistorianGrpcTagClient (browse + metadata)

DRY split mirroring HistorianGrpcReadOrchestrator.RunRawQueryOnSession: browse +
GetTagInfos(metadata) gain externally-supplied connection+session seams; per-call
wrappers delegate. Behaviour-preserving (pending.md A1 broadening).

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

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

@@ -39,6 +39,27 @@ internal static class HistorianGrpcTagClient
     private static HistorianTagMetadata? GetTagMetadata(HistorianClientOptions options, string tag, CancellationToken cancellationToken)
     {
         byte[] tagInfos = GetTagInfosRaw(options, [tag], cancellationToken);
+        return ParseTagMetadata(tagInfos);
+    }
+
+    // Spike/Phase-1 seam (pending.md A1): resolve tag metadata against an EXTERNALLY-supplied,
+    // already-authenticated connection + session — i.e. NO Create()/handshake here. The per-call
+    // GetTagMetadata and this seam share the parse tail (ParseTagMetadata) so neither duplicates the
+    // decode logic (DRY).
+    internal static HistorianTagMetadata? GetTagMetadataOnSession(
+        HistorianGrpcConnection connection,
+        HistorianGrpcHandshake.Session session,
+        string tag,
+        HistorianClientOptions options,
+        CancellationToken cancellationToken)
+    {
+        byte[] tagInfos = GetTagInfosRawOnSession(connection, session, [tag], options, cancellationToken);
+        return ParseTagMetadata(tagInfos);
+    }
+
+    // Shared parse tail for both the per-call GetTagMetadata and the reuse-path GetTagMetadataOnSession.
+    private static HistorianTagMetadata? ParseTagMetadata(byte[] tagInfos)
+    {
         if (tagInfos.Length < 4)
         {
             return null;
@@ -69,7 +90,19 @@ internal static class HistorianGrpcTagClient
     {
         using HistorianGrpcConnection connection = HistorianGrpcChannelFactory.Create(options);
         HistorianGrpcHandshake.Session session = HistorianGrpcHandshake.OpenSession(connection, options, cancellationToken);
+        return GetTagInfosRawOnSession(connection, session, tags, options, cancellationToken);
+    }
 
+    // Spike/Phase-1 seam (pending.md A1): issue GetTagInfosFromName against an EXTERNALLY-supplied,
+    // already-authenticated connection + session — i.e. NO Create()/handshake here. GetTagInfosRaw
+    // delegates to this so the per-call path and the reuse path share one query implementation (DRY).
+    internal static byte[] GetTagInfosRawOnSession(
+        HistorianGrpcConnection connection,
+        HistorianGrpcHandshake.Session session,
+        IReadOnlyList<string> tags,
+        HistorianClientOptions options,
+        CancellationToken cancellationToken)
+    {
         var retrievalClient = new GrpcRetrieval.RetrievalService.RetrievalServiceClient(connection.Channel);
         byte[] requestBuffer = BuildTagNamesBuffer(tags);
         GrpcRetrieval.GetTagInfosFromNameResponse response = retrievalClient.GetTagInfosFromName(
@@ -112,6 +145,8 @@ internal static class HistorianGrpcTagClient
         return Task.Run(() => GetTagExtendedProperties(options, tag, cancellationToken), cancellationToken);
     }
 
+    // No …OnSession seam: extended-properties browse stays per-call (not amortized through the session
+    // pool — out of A1-broadening scope). Add a seam here only if the pool ever needs to route it.
     /// <summary>
     /// Issues a single page-0 <c>GetTagExtendedPropertiesFromName</c> call and returns the raw native
     /// <c>btTeps</c> response buffer (empty when the server reports no rows / non-success). Internal so
@@ -222,6 +257,20 @@ internal static class HistorianGrpcTagClient
     {
         using HistorianGrpcConnection connection = HistorianGrpcChannelFactory.Create(options);
         HistorianGrpcHandshake.Session session = HistorianGrpcHandshake.OpenSession(connection, options, cancellationToken);
+        return BrowseTagNamesOnSession(connection, session, filter, options, cancellationToken);
+    }
+
+    // Spike/Phase-1 seam (pending.md A1): drive StartTagQuery → paged QueryTag → EndTagQuery against an
+    // EXTERNALLY-supplied, already-authenticated connection + session — i.e. NO Create()/handshake here.
+    // BrowseTagNames delegates to this so the per-call path and the reuse path share one browse
+    // implementation (DRY).
+    internal static List<string> BrowseTagNamesOnSession(
+        HistorianGrpcConnection connection,
+        HistorianGrpcHandshake.Session session,
+        string filter,
+        HistorianClientOptions options,
+        CancellationToken cancellationToken)
+    {
         var retrievalClient = new GrpcRetrieval.RetrievalService.RetrievalServiceClient(connection.Channel);
         DateTime Deadline() => DateTime.UtcNow.Add(options.RequestTimeout);
 

tests/AVEVA.Historian.Client.Tests/TagClientOnSessionSeamTests.cs

@@ -0,0 +1,22 @@
+using System.Reflection;
+using AVEVA.Historian.Client.Grpc;
+using Xunit;
+
+namespace AVEVA.Historian.Client.Tests;
+
+public class TagClientOnSessionSeamTests
+{
+    [Theory]
+    [InlineData("BrowseTagNamesOnSession")]
+    [InlineData("GetTagInfosRawOnSession")]
+    [InlineData("GetTagMetadataOnSession")]
+    public void TagClient_ExposesOnSessionSeam(string name)
+    {
+        MethodInfo? m = typeof(HistorianGrpcTagClient).GetMethod(
+            name, BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Public);
+        Assert.NotNull(m);
+        ParameterInfo[] ps = m!.GetParameters();
+        Assert.Equal("HistorianGrpcConnection", ps[0].ParameterType.Name);
+        Assert.Equal("Session", ps[1].ParameterType.Name);
+    }
+}