.NET: Fix Error 404 Agent Hosted MCP

dotnet/src/Microsoft.Agents.AI.AzureAI/AzureAIProjectChatClient.cs

@@ -64,13 +64,27 @@ internal AzureAIProjectChatClient(AIProjectClient aiProjectClient, AgentRecord a
     internal AzureAIProjectChatClient(AIProjectClient aiProjectClient, AgentVersion agentVersion, ChatOptions? chatOptions)
         : this(
               aiProjectClient,
-              new AgentReference(Throw.IfNull(agentVersion).Name, agentVersion.Version),
+              CreateAgentReference(Throw.IfNull(agentVersion)),
               (agentVersion.Definition as PromptAgentDefinition)?.Model,
               chatOptions)
     {
         this._agentVersion = agentVersion;
     }
 
+    /// <summary>
+    /// Creates an <see cref="AgentReference"/> from an <see cref="AgentVersion"/>.
+    /// Uses the agent version's version if available, otherwise defaults to "latest".
+    /// </summary>
+    /// <param name="agentVersion">The agent version to create a reference from.</param>
+    /// <returns>An <see cref="AgentReference"/> for the specified agent version.</returns>
+    private static AgentReference CreateAgentReference(AgentVersion agentVersion)
+    {
+        // If the version is null, empty, or whitespace, use "latest" as the default.
+        // This handles cases where hosted agents (like MCP agents) may not have a version assigned.
+        var version = string.IsNullOrWhiteSpace(agentVersion.Version) ? "latest" : agentVersion.Version;
+        return new AgentReference(agentVersion.Name, version);
+    }
+
     /// <inheritdoc/>
     public override object? GetService(Type serviceType, object? serviceKey = null)
     {

dotnet/src/Microsoft.Agents.AI.AzureAI/AzureAIProjectChatClientExtensions.cs

@@ -543,9 +543,16 @@ private static ChatClientAgentOptions CreateChatClientAgentOptions(AgentVersion
             }
         }
 
+        // Use the agent version's ID if available, otherwise generate one from name and version.
+        // This handles cases where hosted agents (like MCP agents) may not have an ID assigned.
+        var version = string.IsNullOrWhiteSpace(agentVersion.Version) ? "latest" : agentVersion.Version;
+        var agentId = string.IsNullOrWhiteSpace(agentVersion.Id)
+            ? $"{agentVersion.Name}:{version}"
+            : agentVersion.Id;
+
         var agentOptions = new ChatClientAgentOptions()
         {
-            Id = agentVersion.Id,
+            Id = agentId,
             Name = agentVersion.Name,
             Description = agentVersion.Description,
         };

dotnet/tests/Microsoft.Agents.AI.AzureAI.UnitTests/AzureAIProjectChatClientExtensionsTests.cs

@@ -2384,6 +2384,134 @@ public async Task GetAIAgentAsync_WithUseProvidedChatClientAsIs_PreservesSetting
 
     #endregion
 
+    #region Empty Version and ID Handling Tests
+
+    /// <summary>
+    /// Verify that GetAIAgentAsync handles an agent with empty version by using "latest" as fallback.
+    /// </summary>
+    [Fact]
+    public async Task GetAIAgentAsync_WithEmptyVersion_CreatesAgentSuccessfullyAsync()
+    {
+        // Arrange
+        AIProjectClient client = this.CreateTestAgentClientWithEmptyVersion();
+        var options = new ChatClientAgentOptions
+        {
+            Name = "test-agent",
+            ChatOptions = new ChatOptions { Instructions = "Test" }
+        };
+
+        // Act
+        ChatClientAgent agent = await client.GetAIAgentAsync(options);
+
+        // Assert
+        Assert.NotNull(agent);
+        Assert.IsType<ChatClientAgent>(agent);
+        // Verify the agent ID is generated from server-returned name ("agent_abc123") and "latest"
+        Assert.Equal("agent_abc123:latest", agent.Id);
+    }
+
+    /// <summary>
+    /// Verify that AsAIAgent with AgentRecord handles empty version by using "latest" as fallback.
+    /// </summary>
+    [Fact]
+    public void AsAIAgent_WithAgentRecordEmptyVersion_CreatesAgentWithGeneratedId()
+    {
+        // Arrange
+        AIProjectClient client = this.CreateTestAgentClientWithEmptyVersion();
+        AgentRecord agentRecord = this.CreateTestAgentRecordWithEmptyVersion();
+
+        // Act
+        var agent = client.AsAIAgent(agentRecord);
+
+        // Assert
+        Assert.NotNull(agent);
+        // Verify the agent ID is generated from agent record name ("agent_abc123") and "latest"
+        Assert.Equal("agent_abc123:latest", agent.Id);
+    }
+
+    /// <summary>
+    /// Verify that AsAIAgent with AgentVersion handles empty version by using "latest" as fallback.
+    /// </summary>
+    [Fact]
+    public void AsAIAgent_WithAgentVersionEmptyVersion_CreatesAgentWithGeneratedId()
+    {
+        // Arrange
+        AIProjectClient client = this.CreateTestAgentClientWithEmptyVersion();
+        AgentVersion agentVersion = this.CreateTestAgentVersionWithEmptyVersion();
+
+        // Act
+        var agent = client.AsAIAgent(agentVersion);
+
+        // Assert
+        Assert.NotNull(agent);
+        // Verify the agent ID is generated from agent version name ("agent_abc123") and "latest"
+        Assert.Equal("agent_abc123:latest", agent.Id);
+    }
+
+    /// <summary>
+    /// Verify that GetAIAgentAsync handles an agent with whitespace-only version by using "latest" as fallback.
+    /// </summary>
+    [Fact]
+    public async Task GetAIAgentAsync_WithWhitespaceVersion_CreatesAgentSuccessfullyAsync()
+    {
+        // Arrange
+        AIProjectClient client = this.CreateTestAgentClientWithWhitespaceVersion();
+        var options = new ChatClientAgentOptions
+        {
+            Name = "test-agent",
+            ChatOptions = new ChatOptions { Instructions = "Test" }
+        };
+
+        // Act
+        ChatClientAgent agent = await client.GetAIAgentAsync(options);
+
+        // Assert
+        Assert.NotNull(agent);
+        Assert.IsType<ChatClientAgent>(agent);
+        // Verify the agent ID is generated from server-returned name ("agent_abc123") and "latest"
+        Assert.Equal("agent_abc123:latest", agent.Id);
+    }
+
+    /// <summary>
+    /// Verify that AsAIAgent with AgentRecord handles whitespace-only version by using "latest" as fallback.
+    /// </summary>
+    [Fact]
+    public void AsAIAgent_WithAgentRecordWhitespaceVersion_CreatesAgentWithGeneratedId()
+    {
+        // Arrange
+        AIProjectClient client = this.CreateTestAgentClientWithWhitespaceVersion();
+        AgentRecord agentRecord = this.CreateTestAgentRecordWithWhitespaceVersion();
+
+        // Act
+        var agent = client.AsAIAgent(agentRecord);
+
+        // Assert
+        Assert.NotNull(agent);
+        // Verify the agent ID is generated from agent record name ("agent_abc123") and "latest"
+        Assert.Equal("agent_abc123:latest", agent.Id);
+    }
+
+    /// <summary>
+    /// Verify that AsAIAgent with AgentVersion handles whitespace-only version by using "latest" as fallback.
+    /// </summary>
+    [Fact]
+    public void AsAIAgent_WithAgentVersionWhitespaceVersion_CreatesAgentWithGeneratedId()
+    {
+        // Arrange
+        AIProjectClient client = this.CreateTestAgentClientWithWhitespaceVersion();
+        AgentVersion agentVersion = this.CreateTestAgentVersionWithWhitespaceVersion();
+
+        // Act
+        var agent = client.AsAIAgent(agentVersion);
+
+        // Assert
+        Assert.NotNull(agent);
+        // Verify the agent ID is generated from agent version name ("agent_abc123") and "latest"
+        Assert.Equal("agent_abc123:latest", agent.Id);
+    }
+
+    #endregion
+
     #region ApplyToolsToAgentDefinition Tests
 
     /// <summary>
@@ -2678,6 +2806,54 @@ private AgentRecord CreateTestAgentRecord(AgentDefinition? agentDefinition = nul
         return ModelReaderWriter.Read<AgentRecord>(BinaryData.FromString(TestDataUtil.GetAgentResponseJson(agentDefinition: agentDefinition)))!;
     }
 
+    /// <summary>
+    /// Creates a test AIProjectClient with empty version fields for testing hosted MCP agents.
+    /// </summary>
+    private FakeAgentClient CreateTestAgentClientWithEmptyVersion(string? agentName = null, string? instructions = null, string? description = null, AgentDefinition? agentDefinitionResponse = null)
+    {
+        return new FakeAgentClient(agentName, instructions, description, agentDefinitionResponse, useEmptyVersion: true);
+    }
+
+    /// <summary>
+    /// Creates a test AgentRecord with empty version for testing hosted MCP agents.
+    /// </summary>
+    private AgentRecord CreateTestAgentRecordWithEmptyVersion(AgentDefinition? agentDefinition = null)
+    {
+        return ModelReaderWriter.Read<AgentRecord>(BinaryData.FromString(TestDataUtil.GetAgentResponseJsonWithEmptyVersion(agentDefinition: agentDefinition)))!;
+    }
+
+    /// <summary>
+    /// Creates a test AgentVersion with empty version for testing hosted MCP agents.
+    /// </summary>
+    private AgentVersion CreateTestAgentVersionWithEmptyVersion()
+    {
+        return ModelReaderWriter.Read<AgentVersion>(BinaryData.FromString(TestDataUtil.GetAgentVersionResponseJsonWithEmptyVersion()))!;
+    }
+
+    /// <summary>
+    /// Creates a test AIProjectClient with whitespace-only version fields for testing hosted MCP agents.
+    /// </summary>
+    private FakeAgentClient CreateTestAgentClientWithWhitespaceVersion(string? agentName = null, string? instructions = null, string? description = null, AgentDefinition? agentDefinitionResponse = null)
+    {
+        return new FakeAgentClient(agentName, instructions, description, agentDefinitionResponse, versionMode: VersionMode.Whitespace);
+    }
+
+    /// <summary>
+    /// Creates a test AgentRecord with whitespace-only version for testing hosted MCP agents.
+    /// </summary>
+    private AgentRecord CreateTestAgentRecordWithWhitespaceVersion(AgentDefinition? agentDefinition = null)
+    {
+        return ModelReaderWriter.Read<AgentRecord>(BinaryData.FromString(TestDataUtil.GetAgentResponseJsonWithWhitespaceVersion(agentDefinition: agentDefinition)))!;
+    }
+
+    /// <summary>
+    /// Creates a test AgentVersion with whitespace-only version for testing hosted MCP agents.
+    /// </summary>
+    private AgentVersion CreateTestAgentVersionWithWhitespaceVersion()
+    {
+        return ModelReaderWriter.Read<AgentVersion>(BinaryData.FromString(TestDataUtil.GetAgentVersionResponseJsonWithWhitespaceVersion()))!;
+    }
+
     private const string OpenAPISpec = """
         {
           "openapi": "3.0.3",
@@ -2716,14 +2892,26 @@ private AgentVersion CreateTestAgentVersion()
         return ModelReaderWriter.Read<AgentVersion>(BinaryData.FromString(TestDataUtil.GetAgentVersionResponseJson()))!;
     }
 
+    /// <summary>
+    /// Specifies the version mode for test data generation.
+    /// </summary>
+    private enum VersionMode
+    {
+        Normal,
+        Empty,
+        Whitespace
+    }
+
     /// <summary>
     /// Fake AIProjectClient for testing.
     /// </summary>
     private sealed class FakeAgentClient : AIProjectClient
     {
-        public FakeAgentClient(string? agentName = null, string? instructions = null, string? description = null, AgentDefinition? agentDefinitionResponse = null)
+        public FakeAgentClient(string? agentName = null, string? instructions = null, string? description = null, AgentDefinition? agentDefinitionResponse = null, bool useEmptyVersion = false, VersionMode versionMode = VersionMode.Normal)
         {
-            this.Agents = new FakeAIProjectAgentsOperations(agentName, instructions, description, agentDefinitionResponse);
+            // Handle backward compatibility with bool parameter
+            var effectiveVersionMode = useEmptyVersion ? VersionMode.Empty : versionMode;
+            this.Agents = new FakeAIProjectAgentsOperations(agentName, instructions, description, agentDefinitionResponse, effectiveVersionMode);
         }
 
         public override ClientConnection GetConnection(string connectionId)
@@ -2739,60 +2927,82 @@ private sealed class FakeAIProjectAgentsOperations : AIProjectAgentsOperations
             private readonly string? _instructions;
             private readonly string? _description;
             private readonly AgentDefinition? _agentDefinition;
+            private readonly VersionMode _versionMode;
 
-            public FakeAIProjectAgentsOperations(string? agentName = null, string? instructions = null, string? description = null, AgentDefinition? agentDefinitionResponse = null)
+            public FakeAIProjectAgentsOperations(string? agentName = null, string? instructions = null, string? description = null, AgentDefinition? agentDefinitionResponse = null, VersionMode versionMode = VersionMode.Normal)
             {
                 this._agentName = agentName;
                 this._instructions = instructions;
                 this._description = description;
                 this._agentDefinition = agentDefinitionResponse;
+                this._versionMode = versionMode;
+            }
+
+            private string GetAgentResponseJson()
+            {
+                return this._versionMode switch
+                {
+                    VersionMode.Empty => TestDataUtil.GetAgentResponseJsonWithEmptyVersion(this._agentName, this._agentDefinition, this._instructions, this._description),
+                    VersionMode.Whitespace => TestDataUtil.GetAgentResponseJsonWithWhitespaceVersion(this._agentName, this._agentDefinition, this._instructions, this._description),
+                    _ => TestDataUtil.GetAgentResponseJson(this._agentName, this._agentDefinition, this._instructions, this._description)
+                };
+            }
+
+            private string GetAgentVersionResponseJson()
+            {
+                return this._versionMode switch
+                {
+                    VersionMode.Empty => TestDataUtil.GetAgentVersionResponseJsonWithEmptyVersion(this._agentName, this._agentDefinition, this._instructions, this._description),
+                    VersionMode.Whitespace => TestDataUtil.GetAgentVersionResponseJsonWithWhitespaceVersion(this._agentName, this._agentDefinition, this._instructions, this._description),
+                    _ => TestDataUtil.GetAgentVersionResponseJson(this._agentName, this._agentDefinition, this._instructions, this._description)
+                };
             }
 
             public override ClientResult GetAgent(string agentName, RequestOptions options)
             {
-                var responseJson = TestDataUtil.GetAgentResponseJson(this._agentName, this._agentDefinition, this._instructions, this._description);
+                var responseJson = this.GetAgentResponseJson();
                 return ClientResult.FromValue(ModelReaderWriter.Read<AgentRecord>(BinaryData.FromString(responseJson))!, new MockPipelineResponse(200, BinaryData.FromString(responseJson)));
             }
 
             public override ClientResult<AgentRecord> GetAgent(string agentName, CancellationToken cancellationToken = default)
             {
-                var responseJson = TestDataUtil.GetAgentResponseJson(this._agentName, this._agentDefinition, this._instructions, this._description);
+                var responseJson = this.GetAgentResponseJson();
                 return ClientResult.FromValue(ModelReaderWriter.Read<AgentRecord>(BinaryData.FromString(responseJson))!, new MockPipelineResponse(200));
             }
 
             public override Task<ClientResult> GetAgentAsync(string agentName, RequestOptions options)
             {
-                var responseJson = TestDataUtil.GetAgentResponseJson(this._agentName, this._agentDefinition, this._instructions, this._description);
+                var responseJson = this.GetAgentResponseJson();
                 return Task.FromResult<ClientResult>(ClientResult.FromValue(ModelReaderWriter.Read<AgentRecord>(BinaryData.FromString(responseJson))!, new MockPipelineResponse(200, BinaryData.FromString(responseJson))));
             }
 
             public override Task<ClientResult<AgentRecord>> GetAgentAsync(string agentName, CancellationToken cancellationToken = default)
             {
-                var responseJson = TestDataUtil.GetAgentResponseJson(this._agentName, this._agentDefinition, this._instructions, this._description);
+                var responseJson = this.GetAgentResponseJson();
                 return Task.FromResult(ClientResult.FromValue(ModelReaderWriter.Read<AgentRecord>(BinaryData.FromString(responseJson))!, new MockPipelineResponse(200)));
             }
 
             public override ClientResult CreateAgentVersion(string agentName, BinaryContent content, RequestOptions? options = null)
             {
-                var responseJson = TestDataUtil.GetAgentVersionResponseJson(this._agentName, this._agentDefinition, this._instructions, this._description);
+                var responseJson = this.GetAgentVersionResponseJson();
                 return ClientResult.FromValue(ModelReaderWriter.Read<AgentVersion>(BinaryData.FromString(responseJson))!, new MockPipelineResponse(200, BinaryData.FromString(responseJson)));
             }
 
             public override ClientResult<AgentVersion> CreateAgentVersion(string agentName, AgentVersionCreationOptions? options = null, CancellationToken cancellationToken = default)
             {
-                var responseJson = TestDataUtil.GetAgentVersionResponseJson(this._agentName, this._agentDefinition, this._instructions, this._description);
+                var responseJson = this.GetAgentVersionResponseJson();
                 return ClientResult.FromValue(ModelReaderWriter.Read<AgentVersion>(BinaryData.FromString(responseJson))!, new MockPipelineResponse(200));
             }
 
             public override Task<ClientResult> CreateAgentVersionAsync(string agentName, BinaryContent content, RequestOptions? options = null)
             {
-                var responseJson = TestDataUtil.GetAgentVersionResponseJson(this._agentName, this._agentDefinition, this._instructions, this._description);
+                var responseJson = this.GetAgentVersionResponseJson();
                 return Task.FromResult<ClientResult>(ClientResult.FromValue(ModelReaderWriter.Read<AgentVersion>(BinaryData.FromString(responseJson))!, new MockPipelineResponse(200, BinaryData.FromString(responseJson))));
             }
 
             public override Task<ClientResult<AgentVersion>> CreateAgentVersionAsync(string agentName, AgentVersionCreationOptions? options = null, CancellationToken cancellationToken = default)
             {
-                var responseJson = TestDataUtil.GetAgentVersionResponseJson(this._agentName, this._agentDefinition, this._instructions, this._description);
+                var responseJson = this.GetAgentVersionResponseJson();
                 return Task.FromResult(ClientResult.FromValue(ModelReaderWriter.Read<AgentVersion>(BinaryData.FromString(responseJson))!, new MockPipelineResponse(200)));
             }
         }