.NET: fix: avoid local history when service returns conversation id

dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgent.cs

@@ -242,6 +242,7 @@ protected override async Task<AgentResponse> RunCoreAsync(
         // so let's update it and set the conversation id for the service session case.
         var forceEndOfRunPersistence = chatOptions?.ContinuationToken is not null || chatOptions?.AllowBackgroundResponses is true;
         this.UpdateSessionConversationIdAtEndOfRun(safeSession, chatResponse.ConversationId, cancellationToken, forceUpdate: forceEndOfRunPersistence);
+        chatOptions = SetResponseConversationId(chatOptions, chatResponse.ConversationId);
 
         // Ensure that the author name is set for each message in the response.
         foreach (ChatMessage chatResponseMessage in chatResponse.Messages)
@@ -387,6 +388,7 @@ protected override async IAsyncEnumerable<AgentResponseUpdate> RunCoreStreamingA
             // We can derive the type of supported session from whether we have a conversation id,
             // so let's update it and set the conversation id for the service session case.
             this.UpdateSessionConversationIdAtEndOfRun(safeSession, chatResponse.ConversationId, cancellationToken, forceUpdate: forceEndOfRunPersistence);
+            chatOptions = SetResponseConversationId(chatOptions, chatResponse.ConversationId);
 
             // Notify providers of all new messages unless persistence is handled per-service-call by the decorator.
             // When resuming from a continuation token or using background responses, force notification
@@ -1006,6 +1008,18 @@ private void WarnOnMissingPerServiceCallChatHistoryPersistingChatClient()
         return provider;
     }
 
+    private static ChatOptions? SetResponseConversationId(ChatOptions? chatOptions, string? responseConversationId)
+    {
+        if (string.IsNullOrWhiteSpace(responseConversationId))
+        {
+            return chatOptions;
+        }
+
+        chatOptions ??= new();
+        chatOptions.ConversationId ??= responseConversationId;
+        return chatOptions;
+    }
+
     /// <summary>
     /// Loads chat history from the resolved <see cref="ChatHistoryProvider"/> and prepends it to the given messages.
     /// </summary>

dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgent_ChatHistoryManagementTests.cs

@@ -385,8 +385,8 @@ public async Task RunAsync_Throws_WhenThrowEnabledRegardlessOfClearSettingAsync(
     }
 
     /// <summary>
-    /// Verify that RunAsync does not throw when no ChatHistoryProvider is configured on options,
-    /// even if the service returns a conversation id (default InMemoryChatHistoryProvider is used but not from options).
+    /// Verify that RunAsync does not throw or persist local history when no ChatHistoryProvider is configured on options,
+    /// even if the service returns a conversation id.
     /// </summary>
     [Fact]
     public async Task RunAsync_DoesNotThrow_WhenNoChatHistoryProviderInOptionsAndConversationIdReturnedAsync()
@@ -407,8 +407,11 @@ public async Task RunAsync_DoesNotThrow_WhenNoChatHistoryProviderInOptionsAndCon
         ChatClientAgentSession? session = await agent.CreateSessionAsync() as ChatClientAgentSession;
         await agent.RunAsync([new(ChatRole.User, "test")], session);
 
-        // Assert - no exception, session gets the conversation id
+        // Assert - no exception, session gets the conversation id, and local history is not also persisted.
         Assert.Equal("ConvId", session!.ConversationId);
+        var inMemoryProvider = agent.ChatHistoryProvider as InMemoryChatHistoryProvider;
+        Assert.NotNull(inMemoryProvider);
+        Assert.Empty(inMemoryProvider.GetMessages(session));
     }
 
     #endregion