[.Net] Fix #3306 (#3310)

* break conversation when orchestartor return null

* enable test on different OS

.github/workflows/dotnet-build.yml

@@ -43,12 +43,16 @@ jobs:
         if: steps.filter.outputs.workflows == 'true'
   build:
     name: Dotnet Build
-    runs-on: ubuntu-latest
     needs: paths-filter
     if: needs.paths-filter.outputs.hasChanges == 'true'
     defaults:
       run:
         working-directory: dotnet
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ ubuntu-latest, macos-latest, windows-latest ]
+    runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v4
       with:
@@ -92,7 +96,7 @@ jobs:
     - name: Setup dotnet
       uses: actions/setup-dotnet@v4
       with:
-        global-json-file: dotnet/global.json
+        dotnet-version: '8.0.x'
 
     - name: publish AOT testApp, assert static analysis warning count, and run the app
       shell: pwsh
@@ -181,12 +185,14 @@ jobs:
       env:
         AZURE_ARTIFACTS_FEED_URL: https://devdiv.pkgs.visualstudio.com/DevDiv/_packaging/AutoGen/nuget/v3/index.json
         NUGET_AUTH_TOKEN: ${{ secrets.AZURE_DEVOPS_TOKEN }}
+      continue-on-error: true
     - name: Publish nightly package to github package
       run: |
         echo "Publish nightly package to github package"
         echo "ls output directory"
         ls -R ./output/nightly
         dotnet nuget push --api-key ${{ secrets.GITHUB_TOKEN }} --source "https://nuget.pkg.github.com/microsoft/index.json" ./output/nightly/*.nupkg --skip-duplicate
+      continue-on-error: true
     - name: Publish nightly package to agentchat myget feed
       run: |
         echo "Publish nightly package to agentchat myget feed"
@@ -195,3 +201,5 @@ jobs:
         dotnet nuget push --api-key ${{ secrets.MYGET_TOKEN }} --source "https://www.myget.org/F/agentchat/api/v3/index.json" ./output/nightly/*.nupkg --skip-duplicate
       env:
         MYGET_TOKEN: ${{ secrets.MYGET_TOKEN }}
+      continue-on-error: true
+      

dotnet/src/AutoGen.Core/Extension/GroupChatExtension.cs

@@ -43,6 +43,13 @@ public static class GroupChatExtension
         while (maxRound-- > 0)
         {
             var messages = await groupChat.CallAsync(chatHistory, maxRound: 1, cancellationToken);
+
+            // if no new messages, break the loop
+            if (messages.Count() == chatHistory.Count())
+            {
+                yield break;
+            }
+
             var lastMessage = messages.Last();
 
             yield return lastMessage;

dotnet/test/AutoGen.Tests/GroupChat/GroupChatTests.cs

@@ -85,4 +85,29 @@ public class GroupChatTests
 
         chatHistory.Count().Should().Be(2);
     }
+
+    [Fact]
+    public async Task ItTerminateConversationWhenNoSpeakerAvailable()
+    {
+        // fix #3306
+        var alice = new DefaultReplyAgent("Alice", "I am alice");
+        var bob = new DefaultReplyAgent("Bob", "I am bob");
+        var cathy = new DefaultReplyAgent("Cathy", $"I am cathy, {GroupChatExtension.TERMINATE}");
+
+        var orchestrator = Mock.Of<IOrchestrator>();
+        Mock.Get(orchestrator).Setup(x => x.GetNextSpeakerAsync(It.IsAny<OrchestrationContext>(), It.IsAny<CancellationToken>()))
+            .ReturnsAsync((IAgent?)null);
+
+        var groupChat = new GroupChat([alice, bob, cathy], orchestrator);
+
+        var chatHistory = new List<IMessage>();
+
+        var maxRound = 10;
+        await foreach (var message in groupChat.SendAsync(chatHistory, maxRound))
+        {
+            chatHistory.Add(message);
+        }
+
+        chatHistory.Count().Should().Be(0);
+    }
 }