fix: idempotent HistorianSession.DisposeAsync + upfront cancellation check

src/AVEVA.Historian.Client/HistorianSession.cs

@@ -13,6 +13,7 @@ public sealed class HistorianSession : IAsyncDisposable
     private readonly HistorianGrpcConnection _connection;
     private readonly HistorianGrpcHandshake.Session _session;
     private readonly HistorianClientOptions _options;
+    private int _disposed;
 
     /// <summary>Whether this session was opened read-only or write-enabled (the Open2 connection mode).</summary>
     public HistorianSessionKind Kind { get; }
@@ -41,6 +42,7 @@ public sealed class HistorianSession : IAsyncDisposable
         int maxValues,
         [EnumeratorCancellation] CancellationToken ct = default)
     {
+        ct.ThrowIfCancellationRequested();
         var orch = new HistorianGrpcReadOrchestrator(_options);
         IReadOnlyList<HistorianSample> rows = await Task.Run(
             () => orch.RunRawQueryOnSession(_connection, _session.ClientHandle, tag, startUtc, endUtc, maxValues, ct), ct)
@@ -63,6 +65,7 @@ public sealed class HistorianSession : IAsyncDisposable
         TimeSpan interval,
         [EnumeratorCancellation] CancellationToken ct = default)
     {
+        ct.ThrowIfCancellationRequested();
         var orch = new HistorianGrpcReadOrchestrator(_options);
         IReadOnlyList<HistorianAggregateSample> rows = await Task.Run(
             () => orch.RunAggregateQueryOnSession(_connection, _session.ClientHandle, tag, startUtc, endUtc, mode, interval, ct), ct)
@@ -179,8 +182,11 @@ public sealed class HistorianSession : IAsyncDisposable
     /// <summary>Disposes the underlying gRPC connection (closes the channel). The server-side session
     /// also idle-expires on its own; this releases the local channel resources immediately.</summary>
     public ValueTask DisposeAsync()
+    {
+        if (Interlocked.Exchange(ref _disposed, 1) == 0)
         {
             _connection.Dispose();
+        }
         return ValueTask.CompletedTask;
     }
 }