diff --git a/tests/Volcanic.AgenticCore.Telegram.Tests/A2AClientHostTests.cs b/tests/Volcanic.AgenticCore.Telegram.Tests/A2AClientHostTests.cs
index cbec119..08e2d17 100644
--- a/tests/Volcanic.AgenticCore.Telegram.Tests/A2AClientHostTests.cs
+++ b/tests/Volcanic.AgenticCore.Telegram.Tests/A2AClientHostTests.cs
@@ -4,6 +4,9 @@ using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging.Abstractions;
 using Volcanic.AgenticCore.A2A.Server;
+using Volcanic.AgenticCore.A2A.Server.Agent;
+using Volcanic.AgenticCore.A2A.Server.Callers;
+using Volcanic.AgenticCore.Features.Extensions;
 using Volcanic.AgenticCore.Extensions.A2A;
 using Volcanic.AgenticCore.Telegram.A2A;
 using Volcanic.AgenticCore.Telegram.Tests.Support;
@@ -160,4 +163,38 @@ public class A2AClientHostTests
         await Wait.UntilAsync(() => PendingFile.Read(ws).Count == 0, "the record to be removed");
         await ((IHostedService)service).StopAsync(CancellationToken.None);
     }
+
+    [Fact]
+    public async Task BothOn_A2aServerSessionHasNoA2aTool_ChatHasIt()
+    {
+        var client = new A2AClientSettings { Enabled = true };
+        var server = new A2AHostOptions { Enabled = true, PublicUrl = "https://bot.example" };
+        await using var registry = new A2AWatchRegistry(TimeProvider.System, new HttpClientHandler());
+        await using var host = new ChatHost((h, s) =>
+        {
+            s.AddLogging();
+            s.AddSingleton(_ => h.Chats);
+            s.AddSingleton(_ => h.Settings);
+            TelegramA2AClientSetup.Register(s, client, server, registry); // as Program.cs: before the server setup
+            TelegramA2ASetup.Register(s, h.Options, server);
+        }, a2aClient: client);
+        Assert.Contains((await host.ChatAsync()).Session.Tools, t => t.Name == "a2a");
+        var pool = host.Services.GetRequiredService<A2ASessionPool>();
+        var caller = new A2ACaller("travel-bot", "isolated", host.WorkspaceOf(), $"telegram-{Updates.AllowedUser}", Updates.AllowedUser.ToString());
+        using var lease = await pool.AcquireAsync(caller, "ctx1", "task1", CancellationToken.None);
+        Assert.DoesNotContain(lease.Session.Tools, t => t.Name == "a2a");
+        Assert.NotEmpty(lease.Session.Tools);
+    }
+
+    [Fact]
+    public async Task ClientExtension_CannotBeActivatedHostWide()
+    {
+        // As if discovered from an extensions folder: its target can't come from DI, so it never loads host-wide.
+        await using var host = new ChatHost((_, s) => s.AddSingleton(new A2AClientSettings { Enabled = true }),
+            core: o => o.Extensions.Add(ExtensionRegistration.FromType(typeof(A2AClientExtension), "test")));
+        var chat = await host.ChatAsync();
+        Assert.DoesNotContain(chat.Session.Tools, t => t.Name == "a2a");
+        var registration = ExtensionRegistration.FromType(typeof(A2AClientExtension), "test");
+        Assert.ThrowsAny<InvalidOperationException>(() => registration.Factory(host.Services));
+    }
 }