From 6882e003f5e58d154575907f1f5fdd14a25693b0 Mon Sep 17 00:00:00 2001
From: westey <164392973+westey-m@users.noreply.github.com>
Date: Mon, 9 Jun 2025 16:21:42 +0100
Subject: [PATCH] Add IMessagesRetrievableThread interface (#63)

* Add a MessageAgentThread and GetService for Thread

* Remove redundant check and experimental attribuet.

* Address PR comments.

* Fix file name.

* Update comments.

* Remove GetService
---
 .../IMessagesRetrievableThread.cs             | 37 +++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 dotnet/src/Microsoft.Agents.Abstractions/IMessagesRetrievableThread.cs

diff --git a/dotnet/src/Microsoft.Agents.Abstractions/IMessagesRetrievableThread.cs b/dotnet/src/Microsoft.Agents.Abstractions/IMessagesRetrievableThread.cs
new file mode 100644
index 0000000000..ed0688794c
--- /dev/null
+++ b/dotnet/src/Microsoft.Agents.Abstractions/IMessagesRetrievableThread.cs
@@ -0,0 +1,37 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using Microsoft.Extensions.AI;
+
+namespace Microsoft.Agents;
+
+/// <summary>
+/// An interface for agent threads that allow retrieval of messages in the thread for agent invocation.
+/// </summary>
+/// <remarks>
+/// <para>
+/// Some agents need to be invoked with all relevant chat history messages in order to produce a result, while some must be invoked
+/// with the id of a server side thread that contains the chat history.
+/// </para>
+/// <para>
+/// This interface can be implemented by all thread types that support the case where the agent is invoked with the chat history.
+/// Implementations must consider the size of the messages provided, so that they do not exceed the maximum size of the context window
+/// of the agent they are used with. Where appropriate, implementations should truncate or summarize messages so that the size of messages
+/// are constrained.
+/// </para>
+/// </remarks>
+public interface IMessagesRetrievableThread
+{
+    /// <summary>
+    /// Asynchronously retrieves all messages to be used for the agent invocation.
+    /// </summary>
+    /// <remarks>
+    /// Messages are returned in ascending chronological order.
+    /// </remarks>
+    /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
+    /// <returns>The messages in the thread.</returns>
+    /// <exception cref="InvalidOperationException">The thread has been deleted.</exception>
+    IAsyncEnumerable<ChatMessage> GetMessagesAsync(CancellationToken cancellationToken = default);
+}