.NET: Fix duplicate Foundry AgentHost port binding

dotnet/src/Microsoft.Agents.AI.Foundry.Hosting/ServiceCollectionExtensions.cs

@@ -65,13 +65,14 @@ public static class FoundryHostingExtensions
     public static IServiceCollection AddFoundryResponses(this IServiceCollection services, Action<FoundryResponsesOptions>? configure = null)
     {
         _ = Throw.IfNull(services);
+        bool agentHostControlsListenPort = IsAgentHostBuilder(services);
         FoundryResponsesOptions configuredOptions = CreateFoundryResponsesOptions(configure);
         bool serverAdded = AddResponsesServerOnce(
             services,
             configuredOptions,
             configure is not null);
         services.AddHealthChecks();
-        ConfigureFoundryListenPort(services);
+        ConfigureFoundryListenPort(services, agentHostControlsListenPort);
         ConfigureFoundryResponsesOptions(
             services,
             configuredOptions,
@@ -121,13 +122,14 @@ public static IServiceCollection AddFoundryResponses(
         _ = Throw.IfNull(services);
         _ = Throw.IfNull(agent);
 
+        bool agentHostControlsListenPort = IsAgentHostBuilder(services);
         FoundryResponsesOptions configuredOptions = CreateFoundryResponsesOptions(configure);
         bool serverAdded = AddResponsesServerOnce(
             services,
             configuredOptions,
             configure is not null);
         services.AddHealthChecks();
-        ConfigureFoundryListenPort(services);
+        ConfigureFoundryListenPort(services, agentHostControlsListenPort);
         ConfigureFoundryResponsesOptions(
             services,
             configuredOptions,
@@ -520,9 +522,10 @@ private sealed class FoundryResponsesServerMarker(
     /// is resolved.
     /// </para>
     /// </remarks>
-    private static void ConfigureFoundryListenPort(IServiceCollection services)
+    private static void ConfigureFoundryListenPort(IServiceCollection services, bool agentHostControlsListenPort)
     {
-        if (services.Any(static d => d.ServiceType == typeof(FoundryListenPortMarker)))
+        if (agentHostControlsListenPort ||
+            services.Any(static d => d.ServiceType == typeof(FoundryListenPortMarker)))
         {
             return;
         }
@@ -540,6 +543,20 @@ private static void ConfigureFoundryListenPort(IServiceCollection services)
             });
     }
 
+    /// <summary>
+    /// Detects the AgentServer builder, which configures its own Kestrel listener during
+    /// <c>AgentHostBuilder.Build()</c>.
+    /// </summary>
+    /// <remarks>
+    /// <c>AgentHostBuilder</c> registers its public <see cref="ServerVersionRegistry"/> instance
+    /// before callers add protocol services. A standalone <see cref="WebApplicationBuilder"/> does
+    /// not have that instance registration and still needs this package to configure the Foundry port.
+    /// </remarks>
+    private static bool IsAgentHostBuilder(IServiceCollection services) =>
+        services.Any(static descriptor =>
+            descriptor.ServiceType == typeof(ServerVersionRegistry) &&
+            descriptor.ImplementationInstance is ServerVersionRegistry);
+
     /// <summary>
     /// Reads the listen port from configuration, applying the same contract as
     /// <see cref="FoundryEnvironment.Port"/>: <see cref="DefaultListenPort"/> when unset, otherwise

dotnet/tests/Foundry.Hosting.IntegrationTests.TestContainer/Program.cs

@@ -51,6 +51,17 @@
     _ => throw new InvalidOperationException($"Unknown IT_SCENARIO '{scenario}'.")
 };
 
+if (scenario == "happy-path")
+{
+    var agentHostBuilder = AgentHost.CreateBuilder(args);
+    agentHostBuilder.Services.AddFoundryResponses(agent);
+    agentHostBuilder.RegisterProtocol("responses", endpoints => endpoints.MapFoundryResponses());
+
+    var agentHostApp = agentHostBuilder.Build();
+    agentHostApp.Run();
+    return;
+}
+
 var builder = WebApplication.CreateBuilder(args);
 
 var port = Environment.GetEnvironmentVariable("PORT");

dotnet/tests/Foundry.Hosting.IntegrationTests/HappyPathHostedAgentTests.cs

@@ -7,16 +7,17 @@
 namespace Foundry.Hosting.IntegrationTests;
 
 /// <summary>
-/// Basic round trip, streaming, and container-instruction behaviour for a hosted Responses agent.
-/// Store and session semantics live in <see cref="HostedResponsesStoreConfigTests"/>.
+/// Basic round trip, streaming, and container-instruction behaviour for a hosted Responses agent
+/// whose server is created by <c>AgentHost.CreateBuilder</c>. Store and session semantics live in
+/// <see cref="HostedResponsesStoreConfigTests"/>.
 /// </summary>
 [Trait("Category", "FoundryHostedAgents")]
 public sealed class HappyPathHostedAgentTests(HappyPathHostedAgentFixture fixture) : IClassFixture<HappyPathHostedAgentFixture>
 {
     private readonly HappyPathHostedAgentFixture _fixture = fixture;
 
     [Fact]
-    public async Task RunAsync_ReturnsNonEmptyTextAsync()
+    public async Task AgentHostBuilder_StartsAndHandlesRequestAsync()
     {
         // Arrange
         var agent = this._fixture.Agent;
@@ -26,6 +27,7 @@ public async Task RunAsync_ReturnsNonEmptyTextAsync()
 
         // Assert
         Assert.False(string.IsNullOrWhiteSpace(response.Text));
+        Assert.Contains("CONTAINER-OK", response.Text, StringComparison.OrdinalIgnoreCase);
     }
 
     [Fact]

dotnet/tests/Foundry.Hosting.IntegrationTests/README.md

@@ -31,6 +31,11 @@ the agent definition by each fixture, drives a `switch` in the test container's
 `Program.cs` to wire up the scenario specific behavior (tools, toolbox, custom storage,
 etc.).
 
+The `happy-path` scenario creates the server with `AgentHost.CreateBuilder`. This covers
+the recommended AgentServer builder, including its port and readiness configuration. The
+remaining scenarios use `WebApplication.CreateBuilder`, so every live run covers both
+supported hosting paths.
+
 ### Session sticky and user-identity scenario
 
 `HostedSessionAndUserIdentityTests` (fixture `UserIdentityHostedAgentFixture`, agent

dotnet/tests/Microsoft.Agents.AI.Foundry.Hosting.UnitTests/FoundryListenPortTests.cs

@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.Net;
 using System.Reflection;
+using System.Threading.Tasks;
 using Microsoft.AspNetCore.Server.Kestrel.Core;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
@@ -15,9 +16,9 @@ namespace Microsoft.Agents.AI.Foundry.Hosting.UnitTests;
 
 /// <summary>
 /// Verifies that <c>AddFoundryResponses</c> adds a Kestrel listener on the Foundry hosted-runtime
-/// port for a plain <c>WebApplication.CreateBuilder</c> (Tier 3) host, so a source (ZIP) deployed
-/// agent passes the platform readiness probe with no Dockerfile pinning the port, and that it
-/// leaves the addresses of a host running outside Foundry alone.
+/// port for a plain <c>WebApplication.CreateBuilder</c> (Tier 3) host, does not duplicate the
+/// listener owned by <c>AgentHost.CreateBuilder</c> (Tier 2), and leaves the addresses of a host
+/// running outside Foundry alone.
 /// </summary>
 /// <remarks>
 /// Every case supplies its values through an in-memory <see cref="IConfiguration"/>, so no test
@@ -137,6 +138,46 @@ public void AddFoundryResponses_CalledTwiceWhenHosted_ListensOnFoundryPortOnce()
         Assert.Equal([FoundryHostingExtensions.DefaultListenPort], GetCodeBackedPorts(services));
     }
 
+    [Fact]
+    public void AddFoundryResponses_WithStandaloneAgentServerCore_ListensOnFoundryPortOnce()
+    {
+        // Arrange
+        var services = CreateServices();
+        services.AddAgentServerCore();
+
+        // Act
+        services.AddFoundryResponses();
+
+        // Assert
+        Assert.Equal([FoundryHostingExtensions.DefaultListenPort], GetCodeBackedPorts(services));
+    }
+
+    [Fact]
+    public async Task AddFoundryResponses_WithAgentHostBuilder_ListensOnFoundryPortOnceAsync()
+    {
+        // Arrange
+        var builder = AgentHost.CreateBuilder(
+        [
+            $"--{FoundryHostingExtensions.FoundryHostingEnvironmentKey}=foundry",
+        ]);
+        var mockAgent = new Mock<AIAgent>();
+        mockAgent.SetupGet(a => a.Name).Returns("test-agent");
+
+        // Act
+        builder.Services.AddFoundryResponses(mockAgent.Object);
+        var app = builder.Build();
+
+        // Assert
+        try
+        {
+            Assert.Equal([FoundryHostingExtensions.DefaultListenPort], GetCodeBackedPorts(app.App.Services));
+        }
+        finally
+        {
+            await app.App.DisposeAsync();
+        }
+    }
+
     /// <summary>
     /// Builds a service collection whose <see cref="IConfiguration"/> carries the supplied values,
     /// marking the process as Foundry-hosted unless <paramref name="hosted"/> says otherwise.
@@ -162,6 +203,11 @@ private static ServiceCollection CreateServices(bool hosted = true, Dictionary<s
     private static List<int> GetCodeBackedPorts(IServiceCollection services)
     {
         using var provider = services.BuildServiceProvider();
+        return GetCodeBackedPorts(provider);
+    }
+
+    private static List<int> GetCodeBackedPorts(IServiceProvider provider)
+    {
         var options = provider.GetRequiredService<IOptions<KestrelServerOptions>>().Value;
 
         var property = typeof(KestrelServerOptions).GetProperty(