.NET: Add declarative HttpRequestAction sample (#5572)

* Add declarative HttpRequestAction support to workflows * Clean up response body for diagnostics and fix tests. * Fix merge with main. * Remove redundant fallback for request content headers. * Add declarative InvokeHttpRequest sample * Fix solution file and update sample yaml comments * Add final newline to sample class to fix formatting failure
2026-06-16 21:04:09 +08:00 · 2026-04-29 12:19:31 -07:00
parent 570a4d54c2
commit 6853f64de8
10 changed files with 449 additions and 8 deletions
@@ -163,10 +163,10 @@
    <Project Path="samples/02-agents/AgentsWithFoundry/Agent_Step25_ToolboxServerSideTools/Agent_Step25_ToolboxServerSideTools.csproj" />
  </Folder>
  <Folder Name="/Samples/02-agents/Evaluation/">
-    <Project Path="samples/02-agents/Evaluation/Evaluation_SimpleEval/Evaluation_SimpleEval.csproj" />
    <Project Path="samples/02-agents/Evaluation/Evaluation_CustomEvals/Evaluation_CustomEvals.csproj" />
    <Project Path="samples/02-agents/Evaluation/Evaluation_ExpectedOutputs/Evaluation_ExpectedOutputs.csproj" />
    <Project Path="samples/02-agents/Evaluation/Evaluation_Multimodal/Evaluation_Multimodal.csproj" />
+    <Project Path="samples/02-agents/Evaluation/Evaluation_SimpleEval/Evaluation_SimpleEval.csproj" />
  </Folder>
  <Folder Name="/Samples/02-agents/AgentWithMemory/">
    <File Path="samples/02-agents/AgentWithMemory/README.md" />
@@ -226,6 +226,7 @@
    <Project Path="samples/03-workflows/Declarative/HostedWorkflow/HostedWorkflow.csproj" />
    <Project Path="samples/03-workflows/Declarative/InputArguments/InputArguments.csproj" />
    <Project Path="samples/03-workflows/Declarative/InvokeFunctionTool/InvokeFunctionTool.csproj" />
+    <Project Path="samples/03-workflows/Declarative/InvokeHttpRequest/InvokeHttpRequest.csproj" />
    <Project Path="samples/03-workflows/Declarative/InvokeMcpTool/InvokeMcpTool.csproj" />
    <Project Path="samples/03-workflows/Declarative/Marketing/Marketing.csproj" />
    <Project Path="samples/03-workflows/Declarative/StudentTeacher/StudentTeacher.csproj" />
@@ -347,17 +348,17 @@
    <File Path="samples/02-agents/A2A/README.md" />
    <Project Path="samples/02-agents/A2A/A2AAgent_AsFunctionTools/A2AAgent_AsFunctionTools.csproj" />
    <Project Path="samples/02-agents/A2A/A2AAgent_PollingForTaskCompletion/A2AAgent_PollingForTaskCompletion.csproj" />
-    <Project Path="samples/02-agents/A2A/A2AAgent_StreamReconnection/A2AAgent_StreamReconnection.csproj" />
    <Project Path="samples/02-agents/A2A/A2AAgent_ProtocolSelection/A2AAgent_ProtocolSelection.csproj" />
+    <Project Path="samples/02-agents/A2A/A2AAgent_StreamReconnection/A2AAgent_StreamReconnection.csproj" />
  </Folder>  
  <Folder Name="/Samples/05-end-to-end/">
    <Project Path="samples/05-end-to-end/AgentWithPurview/AgentWithPurview.csproj" />
    <Project Path="samples/05-end-to-end/M365Agent/M365Agent.csproj" />
  </Folder>
  <Folder Name="/Samples/05-end-to-end/Evaluation/">
+    <Project Path="samples/05-end-to-end/Evaluation/Evaluation_ConversationSplits/Evaluation_ConversationSplits.csproj" />
    <Project Path="samples/05-end-to-end/Evaluation/Evaluation_FoundryQuality/Evaluation_FoundryQuality.csproj" />
    <Project Path="samples/05-end-to-end/Evaluation/Evaluation_MixedProviders/Evaluation_MixedProviders.csproj" />
-    <Project Path="samples/05-end-to-end/Evaluation/Evaluation_ConversationSplits/Evaluation_ConversationSplits.csproj" />
  </Folder>
  <Folder Name="/Samples/05-end-to-end/A2AClientServer/">
    <File Path="samples/05-end-to-end/A2AClientServer/README.md" />
@@ -543,8 +544,8 @@
    <Project Path="src/Microsoft.Agents.AI.Declarative/Microsoft.Agents.AI.Declarative.csproj" />
    <Project Path="src/Microsoft.Agents.AI.DevUI/Microsoft.Agents.AI.DevUI.csproj" />
    <Project Path="src/Microsoft.Agents.AI.DurableTask/Microsoft.Agents.AI.DurableTask.csproj" />
-    <Project Path="src/Microsoft.Agents.AI.Foundry/Microsoft.Agents.AI.Foundry.csproj" />
    <Project Path="src/Microsoft.Agents.AI.Foundry.Hosting/Microsoft.Agents.AI.Foundry.Hosting.csproj" />
+    <Project Path="src/Microsoft.Agents.AI.Foundry/Microsoft.Agents.AI.Foundry.csproj" />
    <Project Path="src/Microsoft.Agents.AI.GitHub.Copilot/Microsoft.Agents.AI.GitHub.Copilot.csproj" />
    <Project Path="src/Microsoft.Agents.AI.Hosting.A2A.AspNetCore/Microsoft.Agents.AI.Hosting.A2A.AspNetCore.csproj" />
    <Project Path="src/Microsoft.Agents.AI.Hosting.A2A/Microsoft.Agents.AI.Hosting.A2A.csproj" />
@@ -0,0 +1,38 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFrameworks>net10.0</TargetFrameworks>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <InjectIsExternalInitOnLegacy>true</InjectIsExternalInitOnLegacy>
+    <InjectSharedFoundryAgents>true</InjectSharedFoundryAgents>
+    <InjectSharedWorkflowsExecution>true</InjectSharedWorkflowsExecution>
+    <InjectSharedWorkflowsSettings>true</InjectSharedWorkflowsSettings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Configuration" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Binder" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Json" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.UserSecrets" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" />
+    <PackageReference Include="Microsoft.Extensions.Logging" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\..\src\Microsoft.Agents.AI.Workflows.Declarative\Microsoft.Agents.AI.Workflows.Declarative.csproj" />
+    <ProjectReference Include="..\..\..\..\src\Microsoft.Agents.AI.Workflows.Declarative.Foundry\Microsoft.Agents.AI.Workflows.Declarative.Foundry.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Include="InvokeHttpRequest.yaml">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
+</Project>
@@ -0,0 +1,76 @@
+#
+# This workflow demonstrates using HttpRequestAction to call a REST API directly
+# from the workflow without going through an AI agent first.
+#
+# HttpRequestAction allows workflows to:
+# - Fetch data from external HTTP endpoints
+# - Store the parsed response in workflow variables for later use
+# - Add the response body to the conversation so a downstream agent can
+#   answer questions based on it
+#
+# This sample fetches public metadata for the dotnet/runtime repository from
+# the GitHub REST API (no authentication required) and uses an agent to
+# answer follow-up questions about it.
+#
+# Example input:
+# How many subscribers does the repository have?
+#
+kind: Workflow
+trigger:
+
+  kind: OnConversationStart
+  id: workflow_invoke_http_request_demo
+  actions:
+
+    # Capture the original user message for input to the follow-up agent.
+    - kind: SetVariable
+      id: set_user_message
+      variable: Local.InputMessage
+      value: =System.LastMessage
+
+    # Set the repository org/name used to form the request URL.
+    - kind: SetVariable
+      id: set_repo_name
+      variable: Local.RepoName
+      value: microsoft/agent-framework
+
+    # Invoke the GitHub repo API. The response body is parsed into Local.RepoInfo
+    # and also added to the conversation (via conversationId) so the agent below
+    # can answer questions based on it.
+    - kind: HttpRequestAction
+      id: fetch_repo_info
+      conversationId: =System.ConversationId
+      method: GET
+      url: =Concatenate("https://api.github.com/repos/", Local.RepoName)
+      headers:
+        Accept: application/vnd.github+json
+        User-Agent: agent-framework-sample
+      response: Local.RepoInfo
+
+    # Display a confirmation message showing key fields from the parsed response.
+    - kind: SendMessage
+      id: show_repo_summary
+      message: "Fetched repo: visibility={Local.RepoInfo.visibility}, description={Local.RepoInfo.description}"
+
+    # Use the agent to summarize the repo using the conversation context.
+    - kind: InvokeAzureAgent
+      id: summarize_repo
+      conversationId: =System.ConversationId
+      agent:
+        name: GitHubRepoInfoAgent
+      input:
+        messages: =UserMessage("Please provide a brief summary of this GitHub repository based on the data already in the conversation.")
+      output:
+        autoSend: true
+        messages: Local.AgentResponse
+
+    # Allow the user to ask follow-up questions about the repo in a loop.
+    - kind: InvokeAzureAgent
+      id: invoke_followup
+      conversationId: =System.ConversationId
+      agent:
+        name: GitHubRepoInfoAgent
+      input:
+        messages: =Local.InputMessage
+        externalLoop:
+          when: =Upper(System.LastMessage.Text) <> "EXIT"
@@ -0,0 +1,95 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using Azure.AI.Projects;
+using Azure.AI.Projects.Agents;
+using Azure.Identity;
+using Microsoft.Agents.AI.Workflows.Declarative;
+using Microsoft.Extensions.Configuration;
+using Shared.Foundry;
+using Shared.Workflows;
+
+namespace Demo.Workflows.Declarative.InvokeHttpRequest;
+
+/// <summary>
+/// Demonstrates a workflow that uses HttpRequestAction to call a REST API
+/// directly from the workflow.
+/// </summary>
+/// <remarks>
+/// <para>
+/// The HttpRequestAction allows workflows to issue HTTP requests and:
+/// </para>
+/// <list type="bullet">
+/// <item>Fetch data from external REST endpoints</item>
+/// <item>Store the parsed response in workflow variables</item>
+/// <item>Add the response body to the conversation so an agent can answer
+///       questions based on it</item>
+/// </list>
+/// <para>
+/// This sample fetches public metadata for the dotnet/runtime repository from
+/// the GitHub REST API (no authentication required) and uses a Foundry agent
+/// to answer follow-up questions about it. Type "EXIT" to end the conversation.
+/// </para>
+/// <para>
+/// See the README.md file in the parent folder (../README.md) for detailed
+/// information about the configuration required to run this sample.
+/// </para>
+/// </remarks>
+internal sealed class Program
+{
+    public static async Task Main(string[] args)
+    {
+        // Initialize configuration
+        IConfiguration configuration = Application.InitializeConfig();
+        Uri foundryEndpoint = new(configuration.GetValue(Application.Settings.FoundryEndpoint));
+
+        // Ensure sample agent exists in Foundry. The agent has no tools - it answers
+        // questions about the GitHub repository using only the JSON data that the
+        // HttpRequestAction adds to the conversation.
+        await CreateAgentAsync(foundryEndpoint, configuration);
+
+        // Get input from command line or console
+        string workflowInput = Application.GetInput(args);
+
+        // The default HttpRequestHandler is sufficient for this sample because the
+        // GitHub REST endpoint used here does not require authentication. For
+        // authenticated endpoints, supply a custom Func<HttpRequestInfo, ..., HttpClient?>
+        // to DefaultHttpRequestHandler so each request can be routed through a
+        // pre-configured (cached) HttpClient with the appropriate credentials.
+        await using DefaultHttpRequestHandler httpRequestHandler = new();
+
+        // Create the workflow factory with the HTTP request handler
+        WorkflowFactory workflowFactory = new("InvokeHttpRequest.yaml", foundryEndpoint)
+        {
+            HttpRequestHandler = httpRequestHandler
+        };
+
+        // Execute the workflow
+        WorkflowRunner runner = new() { UseJsonCheckpoints = true };
+        await runner.ExecuteAsync(workflowFactory.CreateWorkflow, workflowInput);
+    }
+
+    private static async Task CreateAgentAsync(Uri foundryEndpoint, IConfiguration configuration)
+    {
+        // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
+        AIProjectClient aiProjectClient = new(foundryEndpoint, new DefaultAzureCredential());
+
+        await aiProjectClient.CreateAgentAsync(
+            agentName: "GitHubRepoInfoAgent",
+            agentDefinition: DefineAgent(configuration),
+            agentDescription: "Answers questions about a GitHub repository using HTTP response data in the conversation");
+    }
+
+    private static DeclarativeAgentDefinition DefineAgent(IConfiguration configuration)
+    {
+        return new DeclarativeAgentDefinition(configuration.GetValue(Application.Settings.FoundryModel))
+        {
+            Instructions =
+                """
+                Answer the user's questions about the GitHub repository using only the
+                JSON data already present in the conversation history.
+                If the answer is not contained in the conversation, say so plainly
+                rather than guessing. Be concise and helpful.
+                """
+        };
+    }
+}
@@ -16,6 +16,60 @@ internal static class ChatMessageExtensions
    public static RecordValue ToRecord(this ChatMessage message) =>
        FormulaValue.NewRecordFromFields(message.GetMessageFields());

+    /// <summary>
+    /// Merges the user-authored <paramref name="input"/> with the round-tripped
+    /// <paramref name="inputMessage"/> returned by <c>AgentProvider.CreateMessageAsync</c>
+    /// to produce the value stored in <c>System.LastMessage</c>.
+    /// </summary>
+    /// <remarks>
+    /// The agent service often strips or alters <see cref="TextContent"/> on round-trip,
+    /// while replacing inline media (<see cref="DataContent"/>, <see cref="UriContent"/>)
+    /// with server-side references (typically <see cref="HostedFileContent"/>).
+    /// We want both: the original text (so <c>=System.LastMessage.Text</c> works) and
+    /// the server's media references (so subsequent actions don't re-upload large blobs).
+    /// <para>
+    /// Strategy: keep <paramref name="inputMessage"/> as the base — it has the server-generated
+    /// <see cref="ChatMessage.MessageId"/> and any provider-augmented metadata, and is forward-
+    /// compatible with new properties added on <see cref="ChatMessage"/> in the abstractions
+    /// layer. Only the <see cref="ChatMessage.Contents"/> list is mutated to substitute
+    /// original <see cref="TextContent"/> items in place (and append any extras the round-trip
+    /// dropped). Non-text content items returned by the service are left untouched so
+    /// server-side references survive.
+    /// </para>
+    /// </remarks>
+    public static ChatMessage MergeForLastMessage(this ChatMessage input, ChatMessage? inputMessage)
+    {
+        if (inputMessage is null)
+        {
+            return input;
+        }
+
+        // Build a queue of the original text items, in order. Fall back to ChatMessage.Text
+        // if the input has no explicit TextContent entries.
+        Queue<TextContent> originalTexts = new(input.Contents.OfType<TextContent>());
+        if (originalTexts.Count == 0 && !string.IsNullOrEmpty(input.Text))
+        {
+            originalTexts.Enqueue(new TextContent(input.Text));
+        }
+
+        // Replace TextContent items in inputMessage.Contents with the originals, in order.
+        for (int i = 0; i < inputMessage.Contents.Count && originalTexts.Count > 0; i++)
+        {
+            if (inputMessage.Contents[i] is TextContent)
+            {
+                inputMessage.Contents[i] = originalTexts.Dequeue();
+            }
+        }
+
+        // Append any remaining original text items that the round-trip dropped entirely.
+        while (originalTexts.Count > 0)
+        {
+            inputMessage.Contents.Add(originalTexts.Dequeue());
+        }
+
+        return inputMessage;
+    }
+
    public static TableValue ToTable(this IEnumerable<ChatMessage> messages) =>
        FormulaValue.NewTable(TypeSchema.Message.RecordType, messages.Select(message => message.ToRecord()));

@@ -43,7 +43,11 @@ internal sealed class DeclarativeWorkflowExecutor<TInput>(
        await declarativeContext.QueueConversationUpdateAsync(conversationId, isExternal: true, cancellationToken).ConfigureAwait(false);

        ChatMessage inputMessage = await options.AgentProvider.CreateMessageAsync(conversationId, input, cancellationToken).ConfigureAwait(false);
-        await declarativeContext.SetLastMessageAsync(inputMessage).ConfigureAwait(false);
+
+        // Use the original input for System.LastMessage to ensure Text is preserved (the
+        // service may strip text on round-trip), but substitute server-side media references
+        // (e.g., HostedFileContent) so subsequent actions don't re-upload large blobs.
+        await declarativeContext.SetLastMessageAsync(input.MergeForLastMessage(inputMessage)).ConfigureAwait(false);

        await context.SendResultMessageAsync(this.Id, cancellationToken).ConfigureAwait(false);
    }
@@ -58,7 +58,6 @@ public abstract class RootExecutor<TInput> : Executor<TInput>, IResettableExecut
    public override async ValueTask HandleAsync(TInput message, IWorkflowContext context, CancellationToken cancellationToken)
    {
        DeclarativeWorkflowContext declarativeContext = new(context, this._state);
-        await this.ExecuteAsync(message, declarativeContext, cancellationToken).ConfigureAwait(false);

        ChatMessage input = (this._inputTransform ?? DefaultInputTransform).Invoke(message);

@@ -69,7 +68,13 @@ public abstract class RootExecutor<TInput> : Executor<TInput>, IResettableExecut
        await declarativeContext.QueueConversationUpdateAsync(this._conversationId, isExternal: true, cancellationToken).ConfigureAwait(false);

        ChatMessage inputMessage = await this._agentProvider.CreateMessageAsync(this._conversationId, input, cancellationToken).ConfigureAwait(false);
-        await declarativeContext.SetLastMessageAsync(inputMessage).ConfigureAwait(false);
+
+        // Use the original input for System.LastMessage to ensure Text is preserved (the
+        // service may strip text on round-trip), but substitute server-side media references
+        // (e.g., HostedFileContent) so subsequent actions don't re-upload large blobs.
+        await declarativeContext.SetLastMessageAsync(input.MergeForLastMessage(inputMessage)).ConfigureAwait(false);
+
+        await this.ExecuteAsync(message, declarativeContext, cancellationToken).ConfigureAwait(false);

        await declarativeContext.SendResultMessageAsync(this.Id, cancellationToken).ConfigureAwait(false);
    }
@@ -25,6 +25,9 @@ internal sealed class WorkflowFactory(string workflowFile, Uri foundryEndpoint)
    // Assign to provide MCP tool capabilities
    public IMcpToolHandler? McpToolHandler { get; init; }

+    // Assign to enable HttpRequestAction support
+    public IHttpRequestHandler? HttpRequestHandler { get; init; }
+
    /// <summary>
    /// Create the workflow from the declarative YAML.  Includes definition of the
    /// <see cref="DeclarativeWorkflowOptions" /> and the associated <see cref="ResponseAgentProvider"/>.
@@ -46,6 +49,7 @@ internal sealed class WorkflowFactory(string workflowFile, Uri foundryEndpoint)
                ConversationId = this.ConversationId,
                LoggerFactory = this.LoggerFactory,
                McpToolHandler = this.McpToolHandler,
+                HttpRequestHandler = this.HttpRequestHandler,
            };

        string workflowPath = Path.Combine(AppContext.BaseDirectory, workflowFile);
@@ -162,7 +162,10 @@ internal sealed class WorkflowRunner

                case RequestInfoEvent requestInfo:
                    Debug.WriteLine($"REQUEST #{requestInfo.Request.RequestId}");
-                    externalResponse = requestInfo.Request;
+                    if (response is null || !string.Equals(requestInfo.Request.RequestId, response.RequestId, StringComparison.Ordinal))
+                    {
+                        externalResponse = requestInfo.Request;
+                    }
                    break;

                case ConversationUpdateEvent invokeEvent:
@@ -769,4 +769,165 @@ public sealed class ChatMessageExtensionsTests
                break;
        }
    }
+
+    [Fact]
+    public void MergeForLastMessageReturnsInputWhenInputMessageIsNull()
+    {
+        // Arrange
+        ChatMessage input = new(ChatRole.User, "hello") { MessageId = "local" };
+
+        // Act
+        ChatMessage result = input.MergeForLastMessage(null);
+
+        // Assert
+        Assert.Same(input, result);
+    }
+
+    [Fact]
+    public void MergeForLastMessageReturnsSameInstanceAsRoundTripped()
+    {
+        // Arrange: returning the round-tripped instance keeps the merge forward-compatible
+        // with future ChatMessage properties (e.g., new metadata fields) without explicit copies.
+        ChatMessage input = new(ChatRole.User, "original");
+        ChatMessage roundTripped = new(ChatRole.User, "stripped") { MessageId = "server" };
+
+        // Act
+        ChatMessage result = input.MergeForLastMessage(roundTripped);
+
+        // Assert
+        Assert.Same(roundTripped, result);
+    }
+
+    [Fact]
+    public void MergeForLastMessagePrefersOriginalTextOverRoundTrippedText()
+    {
+        // Arrange
+        ChatMessage input = new(ChatRole.User, "original text");
+        ChatMessage roundTripped = new(ChatRole.User, "stripped") { MessageId = "server-id" };
+
+        // Act
+        ChatMessage result = input.MergeForLastMessage(roundTripped);
+
+        // Assert
+        Assert.Equal("server-id", result.MessageId);
+        Assert.Equal("original text", result.Text);
+        TextContent text = Assert.IsType<TextContent>(Assert.Single(result.Contents));
+        Assert.Equal("original text", text.Text);
+    }
+
+    [Fact]
+    public void MergeForLastMessageReplacesTextInPlaceAndKeepsServerMedia()
+    {
+        // Arrange
+        HostedFileContent serverRef = new("file-abc");
+        ChatMessage input = new(ChatRole.User, [new TextContent("look at this:"), new DataContent("data:image/jpeg;base64,QUJD", "image/jpeg")]);
+        ChatMessage roundTripped = new(ChatRole.User, [new TextContent("stripped"), serverRef]) { MessageId = "server-id" };
+
+        // Act
+        ChatMessage result = input.MergeForLastMessage(roundTripped);
+
+        // Assert: server's text slot is replaced with original text; server's media reference is preserved.
+        Assert.Equal("server-id", result.MessageId);
+        Assert.Collection(result.Contents,
+            c => Assert.Equal("look at this:", Assert.IsType<TextContent>(c).Text),
+            c => Assert.Same(serverRef, c));
+    }
+
+    [Fact]
+    public void MergeForLastMessageAppendsOriginalTextWhenRoundTripHasNoTextSlot()
+    {
+        // Arrange: round-tripped message has only media (no text slot to replace).
+        HostedFileContent serverRef = new("file-1");
+        ChatMessage input = new(ChatRole.User, [new TextContent("middle"), new DataContent("data:image/jpeg;base64,QUE=", "image/jpeg")]);
+        ChatMessage roundTripped = new(ChatRole.User, [serverRef]) { MessageId = "id" };
+
+        // Act
+        ChatMessage result = input.MergeForLastMessage(roundTripped);
+
+        // Assert: media kept; original text appended at end.
+        Assert.Collection(result.Contents,
+            c => Assert.Same(serverRef, c),
+            c => Assert.Equal("middle", Assert.IsType<TextContent>(c).Text));
+    }
+
+    [Fact]
+    public void MergeForLastMessageReplacesMultipleTextSlotsInOrder()
+    {
+        // Arrange: input has two text items; round-tripped has two text slots interleaved with media.
+        HostedFileContent firstRef = new("file-1");
+        HostedFileContent secondRef = new("file-2");
+        ChatMessage input = new(ChatRole.User, [new TextContent("first"), new TextContent("second")]);
+        ChatMessage roundTripped = new(ChatRole.User, [firstRef, new TextContent("a"), secondRef, new TextContent("b")]) { MessageId = "id" };
+
+        // Act
+        ChatMessage result = input.MergeForLastMessage(roundTripped);
+
+        // Assert
+        Assert.Collection(result.Contents,
+            c => Assert.Same(firstRef, c),
+            c => Assert.Equal("first", Assert.IsType<TextContent>(c).Text),
+            c => Assert.Same(secondRef, c),
+            c => Assert.Equal("second", Assert.IsType<TextContent>(c).Text));
+    }
+
+    [Fact]
+    public void MergeForLastMessageFallsBackToInputTextWhenInputHasNoTextContent()
+    {
+        // Arrange: ChatMessage(role, "string") populates Text but no explicit TextContent
+        // when Contents is initially empty in some construction paths. Verify we still
+        // recover the original Text via input.Text.
+        ChatMessage input = new(ChatRole.User, "fallback text");
+        ChatMessage roundTripped = new(ChatRole.User, [new TextContent("stripped")]) { MessageId = "id" };
+
+        // Act
+        ChatMessage result = input.MergeForLastMessage(roundTripped);
+
+        // Assert
+        Assert.Equal("fallback text", Assert.IsType<TextContent>(Assert.Single(result.Contents)).Text);
+    }
+
+    [Fact]
+    public void MergeForLastMessagePreservesServerAuthoredProperties()
+    {
+        // Arrange: server (round-trip) is authoritative for metadata. Returning the
+        // round-tripped instance means any future ChatMessage property is automatically
+        // preserved without code changes here.
+        ChatMessage input = new(ChatRole.User, "hi")
+        {
+            AuthorName = "client-side",
+            AdditionalProperties = new AdditionalPropertiesDictionary { ["client"] = "value" },
+        };
+        ChatMessage roundTripped = new(ChatRole.User, [new TextContent("stripped")])
+        {
+            MessageId = "server",
+            AuthorName = "server-side",
+            AdditionalProperties = new AdditionalPropertiesDictionary { ["server"] = "value" },
+        };
+
+        // Act
+        ChatMessage result = input.MergeForLastMessage(roundTripped);
+
+        // Assert
+        Assert.Equal("server", result.MessageId);
+        Assert.Equal("server-side", result.AuthorName);
+        Assert.NotNull(result.AdditionalProperties);
+        Assert.True(result.AdditionalProperties.ContainsKey("server"));
+        Assert.False(result.AdditionalProperties.ContainsKey("client"));
+    }
+
+    [Fact]
+    public void MergeForLastMessageHandlesEmptyInputContents()
+    {
+        // Arrange
+        ChatMessage input = new(ChatRole.User, new List<AIContent>());
+        HostedFileContent serverRef = new("file-only");
+        ChatMessage roundTripped = new(ChatRole.User, [serverRef]) { MessageId = "id" };
+
+        // Act
+        ChatMessage result = input.MergeForLastMessage(roundTripped);
+
+        // Assert: nothing to splice; round-tripped returned unchanged.
+        Assert.Same(roundTripped, result);
+        Assert.Equal("file-only", Assert.IsType<HostedFileContent>(Assert.Single(result.Contents)).FileId);
+    }
 }