diff --git a/dotnet/src/Microsoft.Agents.AI/Compaction/MessageIndex.cs b/dotnet/src/Microsoft.Agents.AI/Compaction/MessageIndex.cs
index f8467eb3ce..dff5b4764f 100644
--- a/dotnet/src/Microsoft.Agents.AI/Compaction/MessageIndex.cs
+++ b/dotnet/src/Microsoft.Agents.AI/Compaction/MessageIndex.cs
@@ -67,11 +67,12 @@ public sealed class MessageIndex
         this.Groups = groups;
         this.Tokenizer = tokenizer;
 
+        // Restore turn counter from the last group that has a TurnIndex
         for (int index = groups.Count - 1; index >= 0; --index)
         {
-            if (this.Groups[0].TurnIndex.HasValue)
+            if (this.Groups[index].TurnIndex.HasValue)
             {
-                this._currentTurn = this.Groups[0].TurnIndex!.Value;
+                this._currentTurn = this.Groups[index].TurnIndex!.Value;
                 break;
             }
         }
@@ -353,11 +354,6 @@ public sealed class MessageIndex
 
     private static bool HasToolCalls(ChatMessage message)
     {
-        if (message.Contents is null)
-        {
-            return false;
-        }
-
         foreach (AIContent content in message.Contents)
         {
             if (content is FunctionCallContent)
diff --git a/dotnet/src/Microsoft.Agents.AI/Compaction/SummarizationCompactionStrategy.cs b/dotnet/src/Microsoft.Agents.AI/Compaction/SummarizationCompactionStrategy.cs
index 0e7c01719c..54c7ab4cdd 100644
--- a/dotnet/src/Microsoft.Agents.AI/Compaction/SummarizationCompactionStrategy.cs
+++ b/dotnet/src/Microsoft.Agents.AI/Compaction/SummarizationCompactionStrategy.cs
@@ -157,11 +157,6 @@ public sealed class SummarizationCompactionStrategy : CompactionStrategy
             }
         }
 
-        if (summarized == 0)
-        {
-            return false;
-        }
-
         // Generate summary using the chat client (single LLM call for all marked groups)
         ChatResponse response = await this.ChatClient.GetResponseAsync(
             [
@@ -180,14 +175,7 @@ public sealed class SummarizationCompactionStrategy : CompactionStrategy
         ChatMessage summaryMessage = new(ChatRole.Assistant, $"[Summary]\n{summaryText}");
         (summaryMessage.AdditionalProperties ??= [])[MessageGroup.SummaryPropertyKey] = true;
 
-        if (insertIndex >= 0)
-        {
-            index.InsertGroup(insertIndex, MessageGroupKind.Summary, [summaryMessage]);
-        }
-        else
-        {
-            index.AddGroup(MessageGroupKind.Summary, [summaryMessage]);
-        }
+        index.InsertGroup(insertIndex, MessageGroupKind.Summary, [summaryMessage]);
 
         return true;
     }
diff --git a/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/CompactingChatClientTests.cs b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/CompactingChatClientTests.cs
new file mode 100644
index 0000000000..80292c7ed8
--- /dev/null
+++ b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/CompactingChatClientTests.cs
@@ -0,0 +1,400 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Agents.AI.Compaction;
+using Microsoft.Extensions.AI;
+using Moq;
+
+namespace Microsoft.Agents.AI.UnitTests.Compaction;
+
+/// <summary>
+/// Contains tests for the <see cref="CompactingChatClient"/> class.
+/// </summary>
+public sealed class CompactingChatClientTests : IDisposable
+{
+    /// <summary>
+    /// Restores the static <see cref="AIAgent.CurrentRunContext"/> after each test.
+    /// </summary>
+    public void Dispose()
+    {
+        SetCurrentRunContext(null);
+    }
+
+    [Fact]
+    public void ConstructorThrowsOnNullStrategyAsync()
+    {
+        Mock<IChatClient> mockInner = new();
+        Assert.Throws<ArgumentNullException>(() => new CompactingChatClient(mockInner.Object, null!));
+    }
+
+    [Fact]
+    public async Task GetResponseAsyncNoContextPassesThroughAsync()
+    {
+        // Arrange — no CurrentRunContext set → passthrough
+        ChatResponse expectedResponse = new([new ChatMessage(ChatRole.Assistant, "Hi")]);
+        Mock<IChatClient> mockInner = new();
+        mockInner.Setup(c => c.GetResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .ReturnsAsync(expectedResponse);
+
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.TokensExceed(100000));
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        List<ChatMessage> messages =
+        [
+            new ChatMessage(ChatRole.User, "Hello"),
+        ];
+
+        // Act
+        ChatResponse response = await client.GetResponseAsync(messages);
+
+        // Assert
+        Assert.Same(expectedResponse, response);
+        mockInner.Verify(c => c.GetResponseAsync(
+            messages,
+            It.IsAny<ChatOptions>(),
+            It.IsAny<CancellationToken>()), Times.Once);
+    }
+
+    [Fact]
+    public async Task GetResponseAsyncWithContextAppliesCompactionAsync()
+    {
+        // Arrange — set CurrentRunContext so compaction runs
+        ChatResponse expectedResponse = new([new ChatMessage(ChatRole.Assistant, "Done")]);
+        List<ChatMessage>? capturedMessages = null;
+        Mock<IChatClient> mockInner = new();
+        mockInner.Setup(c => c.GetResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .Callback<IEnumerable<ChatMessage>, ChatOptions?, CancellationToken>((msgs, _, _) =>
+                capturedMessages = [.. msgs])
+            .ReturnsAsync(expectedResponse);
+
+        // Strategy that always triggers and keeps only 1 group
+        TruncationCompactionStrategy strategy = new(_ => true, minimumPreserved: 1);
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        TestAgentSession session = new();
+        SetRunContext(session);
+
+        List<ChatMessage> messages =
+        [
+            new ChatMessage(ChatRole.User, "Q1"),
+            new ChatMessage(ChatRole.Assistant, "A1"),
+            new ChatMessage(ChatRole.User, "Q2"),
+        ];
+
+        // Act
+        ChatResponse response = await client.GetResponseAsync(messages);
+
+        // Assert — compaction should have removed oldest groups
+        Assert.Same(expectedResponse, response);
+        Assert.NotNull(capturedMessages);
+        Assert.True(capturedMessages!.Count < messages.Count);
+    }
+
+    [Fact]
+    public async Task GetResponseAsyncNoCompactionNeededReturnsOriginalMessagesAsync()
+    {
+        // Arrange — trigger never fires → no compaction
+        ChatResponse expectedResponse = new([new ChatMessage(ChatRole.Assistant, "Hi")]);
+        List<ChatMessage>? capturedMessages = null;
+        Mock<IChatClient> mockInner = new();
+        mockInner.Setup(c => c.GetResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .Callback<IEnumerable<ChatMessage>, ChatOptions?, CancellationToken>((msgs, _, _) =>
+                capturedMessages = [.. msgs])
+            .ReturnsAsync(expectedResponse);
+
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.TokensExceed(100000));
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        TestAgentSession session = new();
+        SetRunContext(session);
+
+        List<ChatMessage> messages =
+        [
+            new ChatMessage(ChatRole.User, "Hello"),
+        ];
+
+        // Act
+        await client.GetResponseAsync(messages);
+
+        // Assert — original messages passed through
+        Assert.NotNull(capturedMessages);
+        Assert.Single(capturedMessages!);
+        Assert.Equal("Hello", capturedMessages[0].Text);
+    }
+
+    [Fact]
+    public async Task GetResponseAsyncWithExistingIndexUpdatesAsync()
+    {
+        // Arrange — call twice to exercise the "existing index" path (state.MessageIndex.Count > 0)
+        Mock<IChatClient> mockInner = new();
+        mockInner.Setup(c => c.GetResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .ReturnsAsync(new ChatResponse([new ChatMessage(ChatRole.Assistant, "OK")]));
+
+        // Strategy that always triggers, keeping 1 group
+        TruncationCompactionStrategy strategy = new(_ => true, minimumPreserved: 1);
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        TestAgentSession session = new();
+        SetRunContext(session);
+
+        List<ChatMessage> messages1 =
+        [
+            new ChatMessage(ChatRole.User, "Q1"),
+            new ChatMessage(ChatRole.Assistant, "A1"),
+            new ChatMessage(ChatRole.User, "Q2"),
+        ];
+
+        // First call — initializes state
+        await client.GetResponseAsync(messages1);
+
+        List<ChatMessage> messages2 =
+        [
+            new ChatMessage(ChatRole.User, "Q1"),
+            new ChatMessage(ChatRole.Assistant, "A1"),
+            new ChatMessage(ChatRole.User, "Q2"),
+            new ChatMessage(ChatRole.Assistant, "A2"),
+            new ChatMessage(ChatRole.User, "Q3"),
+        ];
+
+        // Act — second call exercises the update path
+        ChatResponse response = await client.GetResponseAsync(messages2);
+
+        // Assert
+        Assert.NotNull(response);
+    }
+
+    [Fact]
+    public async Task GetResponseAsyncNullSessionReturnsOriginalAsync()
+    {
+        // Arrange — CurrentRunContext exists but Session is null
+        ChatResponse expectedResponse = new([new ChatMessage(ChatRole.Assistant, "Hi")]);
+        Mock<IChatClient> mockInner = new();
+        mockInner.Setup(c => c.GetResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .ReturnsAsync(expectedResponse);
+
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.TokensExceed(100000));
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        // Set context with null session
+        SetRunContext(null);
+
+        List<ChatMessage> messages = [new ChatMessage(ChatRole.User, "Hello")];
+
+        // Act
+        ChatResponse response = await client.GetResponseAsync(messages);
+
+        // Assert
+        Assert.Same(expectedResponse, response);
+    }
+
+    [Fact]
+    public async Task GetStreamingResponseAsyncNoContextPassesThroughAsync()
+    {
+        // Arrange — no CurrentRunContext
+        Mock<IChatClient> mockInner = new();
+        ChatResponseUpdate[] updates = [new(ChatRole.Assistant, "Hi")];
+        mockInner.Setup(c => c.GetStreamingResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .Returns(ToAsyncEnumerableAsync(updates));
+
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.TokensExceed(100000));
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        List<ChatMessage> messages = [new ChatMessage(ChatRole.User, "Hello")];
+
+        // Act
+        List<ChatResponseUpdate> results = [];
+        await foreach (ChatResponseUpdate update in client.GetStreamingResponseAsync(messages))
+        {
+            results.Add(update);
+        }
+
+        // Assert
+        Assert.Single(results);
+        Assert.Equal("Hi", results[0].Text);
+    }
+
+    [Fact]
+    public async Task GetStreamingResponseAsyncWithContextAppliesCompactionAsync()
+    {
+        // Arrange
+        Mock<IChatClient> mockInner = new();
+        ChatResponseUpdate[] updates = [new(ChatRole.Assistant, "Done")];
+        mockInner.Setup(c => c.GetStreamingResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .Returns(ToAsyncEnumerableAsync(updates));
+
+        TruncationCompactionStrategy strategy = new(_ => true, minimumPreserved: 1);
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        TestAgentSession session = new();
+        SetRunContext(session);
+
+        List<ChatMessage> messages =
+        [
+            new ChatMessage(ChatRole.User, "Q1"),
+            new ChatMessage(ChatRole.Assistant, "A1"),
+            new ChatMessage(ChatRole.User, "Q2"),
+        ];
+
+        // Act
+        List<ChatResponseUpdate> results = [];
+        await foreach (ChatResponseUpdate update in client.GetStreamingResponseAsync(messages))
+        {
+            results.Add(update);
+        }
+
+        // Assert
+        Assert.Single(results);
+        Assert.Equal("Done", results[0].Text);
+    }
+
+    [Fact]
+    public void GetServiceReturnsStrategyForMatchingType()
+    {
+        // Arrange
+        Mock<IChatClient> mockInner = new();
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.TokensExceed(1000));
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        // Act — typeof(Type).IsInstanceOfType(typeof(CompactionStrategy)) is true
+        object? result = client.GetService(typeof(Type));
+
+        // Assert
+        Assert.Same(strategy, result);
+    }
+
+    [Fact]
+    public void GetServiceDelegatesToBaseForNonMatchingType()
+    {
+        // Arrange
+        Mock<IChatClient> mockInner = new();
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.TokensExceed(1000));
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        // Act — typeof(string) doesn't match
+        object? result = client.GetService(typeof(string));
+
+        // Assert — delegates to base (which returns null for unregistered types)
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void GetServiceThrowsOnNullType()
+    {
+        Mock<IChatClient> mockInner = new();
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.TokensExceed(1000));
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        Assert.Throws<ArgumentNullException>(() => client.GetService(null!));
+    }
+
+    [Fact]
+    public void GetServiceWithServiceKeyDelegatesToBase()
+    {
+        // Arrange — non-null serviceKey always delegates
+        Mock<IChatClient> mockInner = new();
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.TokensExceed(1000));
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        // Act
+        object? result = client.GetService(typeof(Type), serviceKey: "mykey");
+
+        // Assert — delegates to base because serviceKey is non-null
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public async Task GetResponseAsyncMessagesNotListCreatesListCopyAsync()
+    {
+        // Arrange — pass IEnumerable (not List<ChatMessage>) to exercise the list copy branch
+        ChatResponse expectedResponse = new([new ChatMessage(ChatRole.Assistant, "Hi")]);
+        Mock<IChatClient> mockInner = new();
+        mockInner.Setup(c => c.GetResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .ReturnsAsync(expectedResponse);
+
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.TokensExceed(100000));
+        CompactingChatClient client = new(mockInner.Object, strategy);
+
+        TestAgentSession session = new();
+        SetRunContext(session);
+
+        // Use an IEnumerable (not a List) to trigger the copy path
+        IEnumerable<ChatMessage> messages = new ChatMessage[] { new(ChatRole.User, "Hello") };
+
+        // Act
+        ChatResponse response = await client.GetResponseAsync(messages);
+
+        // Assert
+        Assert.Same(expectedResponse, response);
+    }
+
+    /// <summary>
+    /// Sets <see cref="AIAgent.CurrentRunContext"/> via reflection.
+    /// </summary>
+    private static void SetCurrentRunContext(AgentRunContext? context)
+    {
+        FieldInfo? field = typeof(AIAgent).GetField("s_currentContext", BindingFlags.NonPublic | BindingFlags.Static);
+        Assert.NotNull(field);
+        object? asyncLocal = field!.GetValue(null);
+        Assert.NotNull(asyncLocal);
+        PropertyInfo? valueProp = asyncLocal!.GetType().GetProperty("Value");
+        Assert.NotNull(valueProp);
+        valueProp!.SetValue(asyncLocal, context);
+    }
+
+    /// <summary>
+    /// Creates an <see cref="AgentRunContext"/> with the given session and sets it as the current context.
+    /// </summary>
+    private static void SetRunContext(AgentSession? session)
+    {
+        Mock<AIAgent> mockAgent = new() { CallBase = true };
+        AgentRunContext context = new(
+            mockAgent.Object,
+            session,
+            new List<ChatMessage> { new(ChatRole.User, "test") },
+            null);
+        SetCurrentRunContext(context);
+    }
+
+    private static async IAsyncEnumerable<ChatResponseUpdate> ToAsyncEnumerableAsync(
+        ChatResponseUpdate[] updates, [EnumeratorCancellation] CancellationToken cancellationToken = default)
+    {
+        foreach (ChatResponseUpdate update in updates)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            yield return update;
+            await Task.CompletedTask;
+        }
+    }
+
+    private sealed class TestAgentSession : AgentSession;
+}
diff --git a/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/MessageIndexTests.cs b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/MessageIndexTests.cs
index 9f0eabf9d8..b1fa5c59cb 100644
--- a/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/MessageIndexTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/MessageIndexTests.cs
@@ -1,5 +1,6 @@
 // Copyright (c) Microsoft. All rights reserved.
 
+using System.Buffers;
 using System.Collections.Generic;
 using Microsoft.Agents.AI.Compaction;
 using Microsoft.Extensions.AI;
@@ -675,4 +676,174 @@ public class MessageIndexTests
         Assert.Equal(5, inserted.ByteCount);
         Assert.Equal(1, inserted.TokenCount); // 5 / 4 = 1 (integer division)
     }
+
+    [Fact]
+    public void ConstructorWithGroupsRestoresTurnIndex()
+    {
+        // Arrange — pre-existing groups with turn indices
+        MessageGroup group1 = new(MessageGroupKind.User, [new ChatMessage(ChatRole.User, "Q1")], 2, 1, turnIndex: 1);
+        MessageGroup group2 = new(MessageGroupKind.AssistantText, [new ChatMessage(ChatRole.Assistant, "A1")], 2, 1, turnIndex: 1);
+        MessageGroup group3 = new(MessageGroupKind.User, [new ChatMessage(ChatRole.User, "Q2")], 2, 1, turnIndex: 2);
+        List<MessageGroup> groups = [group1, group2, group3];
+
+        // Act — constructor should restore _currentTurn from the last group's TurnIndex
+        MessageIndex index = new(groups);
+
+        // Assert — adding a new user message should get turn 3 (restored 2 + 1)
+        index.Update(
+        [
+            new ChatMessage(ChatRole.User, "Q1"),
+            new ChatMessage(ChatRole.Assistant, "A1"),
+            new ChatMessage(ChatRole.User, "Q2"),
+            new ChatMessage(ChatRole.User, "Q3"),
+        ]);
+
+        // The new user group should have TurnIndex 3
+        MessageGroup lastGroup = index.Groups[index.Groups.Count - 1];
+        Assert.Equal(MessageGroupKind.User, lastGroup.Kind);
+        Assert.NotNull(lastGroup.TurnIndex);
+    }
+
+    [Fact]
+    public void ConstructorWithEmptyGroupsHandlesGracefully()
+    {
+        // Arrange & Act — constructor with empty list
+        MessageIndex index = new([]);
+
+        // Assert
+        Assert.Empty(index.Groups);
+    }
+
+    [Fact]
+    public void ConstructorWithGroupsWithoutTurnIndexSkipsRestore()
+    {
+        // Arrange — groups without turn indices (system messages)
+        MessageGroup systemGroup = new(MessageGroupKind.System, [new ChatMessage(ChatRole.System, "Be helpful")], 10, 3, turnIndex: null);
+        List<MessageGroup> groups = [systemGroup];
+
+        // Act — constructor won't find a TurnIndex to restore
+        MessageIndex index = new(groups);
+
+        // Assert
+        Assert.Single(index.Groups);
+    }
+
+    [Fact]
+    public void ComputeTokenCountReturnsTokenCount()
+    {
+        // Arrange — call the public static method directly
+        List<ChatMessage> messages =
+        [
+            new ChatMessage(ChatRole.User, "Hello world"),
+            new ChatMessage(ChatRole.Assistant, "Greetings"),
+        ];
+
+        // Act — use a simple tokenizer that counts words (each word = 1 token)
+        SimpleWordTokenizer tokenizer = new();
+        int tokenCount = MessageIndex.ComputeTokenCount(messages, tokenizer);
+
+        // Assert — "Hello world" = 2, "Greetings" = 1 → 3 total
+        Assert.Equal(3, tokenCount);
+    }
+
+    [Fact]
+    public void ComputeTokenCountEmptyTextReturnsZero()
+    {
+        // Arrange — message with no text content
+        List<ChatMessage> messages =
+        [
+            new ChatMessage(ChatRole.User, [new FunctionCallContent("c1", "fn")]),
+        ];
+
+        SimpleWordTokenizer tokenizer = new();
+        int tokenCount = MessageIndex.ComputeTokenCount(messages, tokenizer);
+
+        // Assert — no text content → 0 tokens
+        Assert.Equal(0, tokenCount);
+    }
+
+    [Fact]
+    public void CreateWithTokenizerUsesTokenizerForCounts()
+    {
+        // Arrange
+        SimpleWordTokenizer tokenizer = new();
+
+        List<ChatMessage> messages =
+        [
+            new ChatMessage(ChatRole.User, "Hello world test"),
+        ];
+
+        // Act
+        MessageIndex index = MessageIndex.Create(messages, tokenizer);
+
+        // Assert — tokenizer counts words: "Hello world test" = 3 tokens
+        Assert.Single(index.Groups);
+        Assert.Equal(3, index.Groups[0].TokenCount);
+        Assert.NotNull(index.Tokenizer);
+    }
+
+    [Fact]
+    public void InsertGroupWithTokenizerUsesTokenizer()
+    {
+        // Arrange
+        SimpleWordTokenizer tokenizer = new();
+        MessageIndex index = MessageIndex.Create(
+        [
+            new ChatMessage(ChatRole.User, "Hello"),
+        ], tokenizer);
+
+        // Act
+        ChatMessage msg = new(ChatRole.Assistant, "Hello world test message");
+        MessageGroup inserted = index.InsertGroup(0, MessageGroupKind.AssistantText, [msg]);
+
+        // Assert — tokenizer counts words: "Hello world test message" = 4 tokens
+        Assert.Equal(4, inserted.TokenCount);
+    }
+
+    /// <summary>
+    /// A simple tokenizer that counts whitespace-separated words as tokens.
+    /// </summary>
+    private sealed class SimpleWordTokenizer : Microsoft.ML.Tokenizers.Tokenizer
+    {
+        public override Microsoft.ML.Tokenizers.PreTokenizer? PreTokenizer => null;
+        public override Microsoft.ML.Tokenizers.Normalizer? Normalizer => null;
+
+        protected override Microsoft.ML.Tokenizers.EncodeResults<Microsoft.ML.Tokenizers.EncodedToken> EncodeToTokens(string? text, System.ReadOnlySpan<char> textSpan, Microsoft.ML.Tokenizers.EncodeSettings settings)
+        {
+            // Simple word-based encoding
+            string input = text ?? textSpan.ToString();
+            if (string.IsNullOrWhiteSpace(input))
+            {
+                return new Microsoft.ML.Tokenizers.EncodeResults<Microsoft.ML.Tokenizers.EncodedToken>
+                {
+                    Tokens = System.Array.Empty<Microsoft.ML.Tokenizers.EncodedToken>(),
+                    CharsConsumed = 0,
+                    NormalizedText = null,
+                };
+            }
+
+            string[] words = input.Split(' ');
+            List<Microsoft.ML.Tokenizers.EncodedToken> tokens = [];
+            int offset = 0;
+            for (int i = 0; i < words.Length; i++)
+            {
+                tokens.Add(new Microsoft.ML.Tokenizers.EncodedToken(i, words[i], new System.Range(offset, offset + words[i].Length)));
+                offset += words[i].Length + 1;
+            }
+
+            return new Microsoft.ML.Tokenizers.EncodeResults<Microsoft.ML.Tokenizers.EncodedToken>
+            {
+                Tokens = tokens,
+                CharsConsumed = input.Length,
+                NormalizedText = null,
+            };
+        }
+
+        public override OperationStatus Decode(System.Collections.Generic.IEnumerable<int> ids, System.Span<char> destination, out int idsConsumed, out int charsWritten)
+        {
+            idsConsumed = 0;
+            charsWritten = 0;
+            return OperationStatus.Done;
+        }
+    }
 }
diff --git a/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/SlidingWindowCompactionStrategyTests.cs b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/SlidingWindowCompactionStrategyTests.cs
index 2d78c2e720..08c3b50ad3 100644
--- a/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/SlidingWindowCompactionStrategyTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/SlidingWindowCompactionStrategyTests.cs
@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft. All rights reserved.
+// Copyright (c) Microsoft. All rights reserved.
 
 using System.Collections.Generic;
 using System.Threading.Tasks;
@@ -163,12 +163,12 @@ public class SlidingWindowCompactionStrategyTests
     {
         // Arrange — trigger on > 1 turn, custom target stops after removing 1 turn
         int removeCount = 0;
-        CompactionTrigger targetAfterOne = _ => ++removeCount >= 1;
+        bool TargetAfterOne(MessageIndex _) => ++removeCount >= 1;
 
         SlidingWindowCompactionStrategy strategy = new(
             CompactionTriggers.TurnsExceed(1),
             minimumPreserved: 0,
-            target: targetAfterOne);
+            target: TargetAfterOne);
 
         MessageIndex index = MessageIndex.Create(
         [
diff --git a/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/SummarizationCompactionStrategyTests.cs b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/SummarizationCompactionStrategyTests.cs
index d12d490dd4..9d6bfdb05b 100644
--- a/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/SummarizationCompactionStrategyTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/SummarizationCompactionStrategyTests.cs
@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft. All rights reserved.
+// Copyright (c) Microsoft. All rights reserved.
 
 using System.Collections.Generic;
 using System.Linq;
@@ -15,8 +15,6 @@ namespace Microsoft.Agents.AI.UnitTests.Compaction;
 /// </summary>
 public class SummarizationCompactionStrategyTests
 {
-    private static readonly CompactionTrigger AlwaysTrigger = _ => true;
-
     /// <summary>
     /// Creates a mock <see cref="IChatClient"/> that returns the specified summary text.
     /// </summary>
@@ -60,7 +58,7 @@ public class SummarizationCompactionStrategyTests
         // Arrange — always trigger, preserve 1 recent group
         SummarizationCompactionStrategy strategy = new(
             CreateMockChatClient("Key facts from earlier."),
-            AlwaysTrigger,
+            CompactionTriggers.Always,
             minimumPreserved: 1);
 
         MessageIndex index = MessageIndex.Create(
@@ -91,7 +89,7 @@ public class SummarizationCompactionStrategyTests
         // Arrange
         SummarizationCompactionStrategy strategy = new(
             CreateMockChatClient(),
-            AlwaysTrigger,
+            CompactionTriggers.Always,
             minimumPreserved: 1);
 
         MessageIndex index = MessageIndex.Create(
@@ -118,7 +116,7 @@ public class SummarizationCompactionStrategyTests
         // Arrange
         SummarizationCompactionStrategy strategy = new(
             CreateMockChatClient("Summary text."),
-            AlwaysTrigger,
+            CompactionTriggers.Always,
             minimumPreserved: 1);
 
         MessageIndex index = MessageIndex.Create(
@@ -145,7 +143,7 @@ public class SummarizationCompactionStrategyTests
         // Arrange — LLM returns whitespace
         SummarizationCompactionStrategy strategy = new(
             CreateMockChatClient("   "),
-            AlwaysTrigger,
+            CompactionTriggers.Always,
             minimumPreserved: 1);
 
         MessageIndex index = MessageIndex.Create(
@@ -168,7 +166,7 @@ public class SummarizationCompactionStrategyTests
         // Arrange — preserve 5 but only 2 non-system groups
         SummarizationCompactionStrategy strategy = new(
             CreateMockChatClient(),
-            AlwaysTrigger,
+            CompactionTriggers.Always,
             minimumPreserved: 5);
 
         MessageIndex index = MessageIndex.Create(
@@ -198,12 +196,12 @@ public class SummarizationCompactionStrategyTests
                 capturedMessages = [.. msgs])
             .ReturnsAsync(new ChatResponse([new ChatMessage(ChatRole.Assistant, "Custom summary.")]));
 
-        const string customPrompt = "Summarize in bullet points only.";
+        const string CustomPrompt = "Summarize in bullet points only.";
         SummarizationCompactionStrategy strategy = new(
             mockClient.Object,
-            AlwaysTrigger,
+            CompactionTriggers.Always,
             minimumPreserved: 1,
-            summarizationPrompt: customPrompt);
+            summarizationPrompt: CustomPrompt);
 
         MessageIndex index = MessageIndex.Create(
         [
@@ -216,7 +214,7 @@ public class SummarizationCompactionStrategyTests
 
         // Assert — the custom prompt should be the first message sent to the LLM
         Assert.NotNull(capturedMessages);
-        Assert.Equal(customPrompt, capturedMessages![0].Text);
+        Assert.Equal(CustomPrompt, capturedMessages![0].Text);
     }
 
     [Fact]
@@ -225,7 +223,7 @@ public class SummarizationCompactionStrategyTests
         // Arrange
         SummarizationCompactionStrategy strategy = new(
             CreateMockChatClient(),
-            AlwaysTrigger,
+            CompactionTriggers.Always,
             minimumPreserved: 1);
 
         MessageIndex index = MessageIndex.Create(
@@ -248,13 +246,13 @@ public class SummarizationCompactionStrategyTests
     {
         // Arrange — 4 non-system groups, preserve 1, target met after 1 exclusion
         int exclusionCount = 0;
-        CompactionTrigger targetAfterOne = _ => ++exclusionCount >= 1;
+        CompactionTrigger TargetAfterOne = _ => ++exclusionCount >= 1;
 
         SummarizationCompactionStrategy strategy = new(
             CreateMockChatClient("Partial summary."),
-            AlwaysTrigger,
+            CompactionTriggers.Always,
             minimumPreserved: 1,
-            target: targetAfterOne);
+            target: TargetAfterOne);
 
         MessageIndex index = MessageIndex.Create(
         [
@@ -278,7 +276,7 @@ public class SummarizationCompactionStrategyTests
         // Arrange — preserve 2
         SummarizationCompactionStrategy strategy = new(
             CreateMockChatClient("Summary."),
-            AlwaysTrigger,
+            CompactionTriggers.Always,
             minimumPreserved: 2);
 
         MessageIndex index = MessageIndex.Create(
diff --git a/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/TruncationCompactionStrategyTests.cs b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/TruncationCompactionStrategyTests.cs
index ee08611653..ceb40b7495 100644
--- a/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/TruncationCompactionStrategyTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/TruncationCompactionStrategyTests.cs
@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft. All rights reserved.
+// Copyright (c) Microsoft. All rights reserved.
 
 using System.Linq;
 using System.Threading.Tasks;
@@ -12,13 +12,11 @@ namespace Microsoft.Agents.AI.UnitTests.Compaction;
 /// </summary>
 public class TruncationCompactionStrategyTests
 {
-    private static readonly CompactionTrigger s_alwaysTrigger = _ => true;
-
     [Fact]
     public async Task CompactAsyncAlwaysTriggerCompactsToPreserveRecentAsync()
     {
         // Arrange — always-trigger means always compact
-        TruncationCompactionStrategy strategy = new(s_alwaysTrigger, minimumPreserved: 1);
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.Always, minimumPreserved: 1);
         MessageIndex groups = MessageIndex.Create(
         [
             new ChatMessage(ChatRole.User, "First"),
@@ -89,7 +87,7 @@ public class TruncationCompactionStrategyTests
     public async Task CompactAsyncPreservesSystemMessagesAsync()
     {
         // Arrange
-        TruncationCompactionStrategy strategy = new(s_alwaysTrigger, minimumPreserved: 1);
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.Always, minimumPreserved: 1);
         MessageIndex groups = MessageIndex.Create(
         [
             new ChatMessage(ChatRole.System, "You are helpful."),
@@ -117,9 +115,9 @@ public class TruncationCompactionStrategyTests
     public async Task CompactAsyncPreservesToolCallGroupAtomicityAsync()
     {
         // Arrange
-        TruncationCompactionStrategy strategy = new(s_alwaysTrigger, minimumPreserved: 1);
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.Always, minimumPreserved: 1);
 
-        ChatMessage assistantToolCall= new(ChatRole.Assistant, [new FunctionCallContent("call1", "get_weather")]);
+        ChatMessage assistantToolCall = new(ChatRole.Assistant, [new FunctionCallContent("call1", "get_weather")]);
         ChatMessage toolResult = new(ChatRole.Tool, "Sunny");
         ChatMessage finalResponse = new(ChatRole.User, "Thanks!");
 
@@ -141,7 +139,7 @@ public class TruncationCompactionStrategyTests
     public async Task CompactAsyncSetsExcludeReasonAsync()
     {
         // Arrange
-        TruncationCompactionStrategy strategy = new(s_alwaysTrigger, minimumPreserved: 1);
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.Always, minimumPreserved: 1);
         MessageIndex groups = MessageIndex.Create(
         [
             new ChatMessage(ChatRole.User, "Old"),
@@ -160,7 +158,7 @@ public class TruncationCompactionStrategyTests
     public async Task CompactAsyncSkipsAlreadyExcludedGroupsAsync()
     {
         // Arrange
-        TruncationCompactionStrategy strategy = new(s_alwaysTrigger, minimumPreserved: 1);
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.Always, minimumPreserved: 1);
         MessageIndex groups = MessageIndex.Create(
         [
             new ChatMessage(ChatRole.User, "Already excluded"),
@@ -183,7 +181,7 @@ public class TruncationCompactionStrategyTests
     public async Task CompactAsyncMinimumPreservedKeepsMultipleAsync()
     {
         // Arrange — keep 2 most recent
-        TruncationCompactionStrategy strategy = new(s_alwaysTrigger, minimumPreserved: 2);
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.Always, minimumPreserved: 2);
         MessageIndex groups = MessageIndex.Create(
         [
             new ChatMessage(ChatRole.User, "Q1"),
@@ -207,7 +205,7 @@ public class TruncationCompactionStrategyTests
     public async Task CompactAsyncNothingToRemoveReturnsFalseAsync()
     {
         // Arrange — preserve 5 but only 2 groups
-        TruncationCompactionStrategy strategy = new(s_alwaysTrigger, minimumPreserved: 5);
+        TruncationCompactionStrategy strategy = new(CompactionTriggers.Always, minimumPreserved: 5);
         MessageIndex groups = MessageIndex.Create(
         [
             new ChatMessage(ChatRole.User, "Hello"),
@@ -226,12 +224,12 @@ public class TruncationCompactionStrategyTests
     {
         // Arrange — always trigger, custom target stops after 1 exclusion
         int targetChecks = 0;
-        CompactionTrigger targetAfterOne = _ => ++targetChecks >= 1;
+        bool TargetAfterOne(MessageIndex _) => ++targetChecks >= 1;
 
         TruncationCompactionStrategy strategy = new(
-            s_alwaysTrigger,
+            CompactionTriggers.Always,
             minimumPreserved: 1,
-            target: targetAfterOne);
+            target: TargetAfterOne);
 
         MessageIndex groups = MessageIndex.Create(
         [
diff --git a/dotnet/tests/Microsoft.Agents.AI.UnitTests/Microsoft.Agents.AI.UnitTests.csproj b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Microsoft.Agents.AI.UnitTests.csproj
index 7fa417b184..ffa4417f34 100644
--- a/dotnet/tests/Microsoft.Agents.AI.UnitTests/Microsoft.Agents.AI.UnitTests.csproj
+++ b/dotnet/tests/Microsoft.Agents.AI.UnitTests/Microsoft.Agents.AI.UnitTests.csproj
@@ -16,6 +16,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.DependencyInjection" />
     <PackageReference Include="Microsoft.Extensions.Logging" />
+    <PackageReference Include="Microsoft.ML.Tokenizers" />
     <PackageReference Include="OpenTelemetry" />
     <PackageReference Include="OpenTelemetry.Exporter.InMemory" />
     <PackageReference Include="System.Linq.AsyncEnumerable" />