Add durable chat history ownership and session persistence

dotnet/src/Microsoft.Agents.AI.DurableTask/DurableAgentCompactionNotSupportedException.cs

@@ -0,0 +1,39 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+namespace Microsoft.Agents.AI.DurableTask;
+
+/// <summary>
+/// The exception thrown when a durable agent is combined with unsupported stateful compaction.
+/// </summary>
+public sealed class DurableAgentCompactionNotSupportedException : NotSupportedException
+{
+    private const string DefaultMessage =
+        "Durable .NET agents do not support directly discoverable stateful chat-history compaction. " +
+        "The current Agent Framework compaction state contains full message copies. Persisting it duplicates " +
+        "transcript content for entity, external-provider, and service-owned conversations, while discarding it " +
+        "loses compaction semantics. Disable stateful compaction for durable execution.";
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="DurableAgentCompactionNotSupportedException"/> class.
+    /// </summary>
+    public DurableAgentCompactionNotSupportedException()
+        : base(DefaultMessage)
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance with a specified error message.
+    /// </summary>
+    public DurableAgentCompactionNotSupportedException(string? message)
+        : base(message)
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance with a specified error message and inner exception.
+    /// </summary>
+    public DurableAgentCompactionNotSupportedException(string? message, Exception? innerException)
+        : base(message, innerException)
+    {
+    }
+}