feat: HistorianSession browse + metadata on the reused session (+ env-gated round-trip)

Browse mirrors ReadRawAsync (collect-then-yield); metadata mirrors ReadAtTimeAsync
(unary). Delegates to the HistorianGrpcTagClient …OnSession seams so a leased session
browses + reads metadata without re-handshaking (pending.md A1 broadening).

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

src/AVEVA.Historian.Client/HistorianSession.cs

@@ -7,7 +7,7 @@ namespace AVEVA.Historian.Client;
 /// <summary>A live, reusable authenticated Historian session: holds one gRPC connection + one
 /// OpenConnection handle and runs ops on them WITHOUT re-handshaking. Reuse across ops amortizes the
 /// auth handshake. Idle-expires server-side in ~20-25s — callers keep it warm (PingAsync) or re-open.
-/// Reads/historical-write/tag-write/status only; events are NOT exposed (separate channel+auth).</summary>
+/// Reads, browse/metadata, historical-write, tag-write and status; events are NOT exposed (separate channel+auth).</summary>
 public sealed class HistorianSession : IAsyncDisposable
 {
     private readonly HistorianGrpcConnection _connection;
@@ -89,6 +89,28 @@ public sealed class HistorianSession : IAsyncDisposable
             () => orch.RunAtTimeOnSession(_connection, _session.ClientHandle, tag, timestampsUtc, ct), ct);
     }
 
+    // --- browse / metadata (call the …OnSession seams, which take the full Session for the string handle) ---
+
+    /// <summary>Browses tag names matching <paramref name="filter"/> on the held session.</summary>
+    public async IAsyncEnumerable<string> BrowseTagNamesAsync(
+        string filter = "*",
+        [EnumeratorCancellation] CancellationToken ct = default)
+    {
+        ct.ThrowIfCancellationRequested();
+        List<string> names = await Task.Run(
+            () => HistorianGrpcTagClient.BrowseTagNamesOnSession(_connection, _session, filter, _options, ct), ct)
+            .ConfigureAwait(false);
+        foreach (string name in names)
+        {
+            ct.ThrowIfCancellationRequested();
+            yield return name;
+        }
+    }
+
+    /// <summary>Reads metadata for <paramref name="tag"/> on the held session (null if unknown).</summary>
+    public Task<HistorianTagMetadata?> GetTagMetadataAsync(string tag, CancellationToken ct = default)
+        => Task.Run(() => HistorianGrpcTagClient.GetTagMetadataOnSession(_connection, _session, tag, _options, ct), ct);
+
     // --- writes (the …OnSession seams take the full Session, since the historical write keys on the
     //     string handle + tag GUID and the tag-config ops mix string/uint handles) ---