feat(a2a-client): scaffold the A2A client extension behind A2AClient__Enabled

VolcanicAgenticCore.slnx

@@ -1,5 +1,6 @@
 <Solution>
   <Folder Name="/extensions/">
+    <Project Path="extensions/Volcanic.AgenticCore.Extensions.A2A/Volcanic.AgenticCore.Extensions.A2A.csproj" />
     <Project Path="extensions/Volcanic.AgenticCore.Extensions.Anthropic/Volcanic.AgenticCore.Extensions.Anthropic.csproj" />
     <Project Path="extensions/Volcanic.AgenticCore.Extensions.ClaudeCode.Bridge/Volcanic.AgenticCore.Extensions.ClaudeCode.Bridge.csproj" />
     <Project Path="extensions/Volcanic.AgenticCore.Extensions.ClaudeCode/Volcanic.AgenticCore.Extensions.ClaudeCode.csproj" />

extensions/Volcanic.AgenticCore.Extensions.A2A/A2AClientSettings.cs

@@ -0,0 +1,23 @@
+namespace Volcanic.AgenticCore.Extensions.A2A;
+
+/// <summary>Section <c>A2AClient</c> (env <c>A2AClient__…</c>). Named so it doesn't clash with the SDK's <c>A2AClientOptions</c>.</summary>
+public sealed class A2AClientSettings
+{
+    public const string SectionName = "A2AClient";
+
+    /// <summary>Off by default: no <c>a2a</c> tool, no watches. Independent of the server's <c>A2A:Enabled</c>.</summary>
+    public bool Enabled { get; set; }
+
+    /// <summary>How long <c>send</c> waits for a result before a watch takes over. 0 hands over at once.</summary>
+    public int WaitSeconds { get; set; } = 60;
+
+    public TimeSpan WatchTimeout { get; set; } = TimeSpan.FromDays(1);
+    public int CardTimeoutSeconds { get; set; } = 10;
+    public long MaxFileBytes { get; set; } = 10 * 1024 * 1024;
+
+    /// <summary>
+    /// Our public base URL for push webhooks (<c>{PushBaseUrl}/a2a/push/{watchId}</c>). Set by the host from the server's
+    /// <c>A2A:PublicUrl</c> only while the server (and so the push receiver) is on; null = subscribe or poll.
+    /// </summary>
+    public string? PushBaseUrl { get; set; }
+}

extensions/Volcanic.AgenticCore.Extensions.A2A/Volcanic.AgenticCore.Extensions.A2A.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <Description>A2A client extension: the a2a tool, remote agents in agents.json, watches for long tasks.</Description>
+  </PropertyGroup>
+  <ItemGroup>
+    <!-- Private="false": the host already ships Abstractions; an extension must not bring its own copy (docs/extensions.md). -->
+    <ProjectReference Include="../../src/Volcanic.AgenticCore.Abstractions/Volcanic.AgenticCore.Abstractions.csproj" Private="false" />
+    <PackageReference Include="A2A" Version="1.0.0-preview2" />
+  </ItemGroup>
+  <ItemGroup>
+    <InternalsVisibleTo Include="Volcanic.AgenticCore.Extensions.Tests" />
+    <InternalsVisibleTo Include="Volcanic.AgenticCore.Telegram.Tests" />
+  </ItemGroup>
+</Project>

src/Volcanic.AgenticCore.A2A.Server/Volcanic.AgenticCore.A2A.Server.csproj

@@ -9,6 +9,7 @@
   </ItemGroup>
   <ItemGroup>
     <InternalsVisibleTo Include="Volcanic.AgenticCore.A2A.Server.Tests" />
+    <InternalsVisibleTo Include="Volcanic.AgenticCore.Extensions.Tests" />
     <InternalsVisibleTo Include="Volcanic.AgenticCore.Telegram.Tests" />
   </ItemGroup>
 </Project>

tests/Volcanic.AgenticCore.Extensions.Tests/A2A/A2AClientSettingsTests.cs

@@ -0,0 +1,19 @@
+using Volcanic.AgenticCore.Extensions.A2A;
+
+namespace Volcanic.AgenticCore.Extensions.Tests.A2A;
+
+public class A2AClientSettingsTests
+{
+    [Fact]
+    public void Defaults_OffWithSpecValues()
+    {
+        var s = new A2AClientSettings();
+        Assert.False(s.Enabled);
+        Assert.Equal(60, s.WaitSeconds);
+        Assert.Equal(TimeSpan.FromDays(1), s.WatchTimeout);
+        Assert.Equal(10, s.CardTimeoutSeconds);
+        Assert.Equal(10 * 1024 * 1024, s.MaxFileBytes);
+        Assert.Null(s.PushBaseUrl);
+        Assert.Equal("A2AClient", A2AClientSettings.SectionName);
+    }
+}

tests/Volcanic.AgenticCore.Extensions.Tests/Volcanic.AgenticCore.Extensions.Tests.csproj

@@ -11,6 +11,8 @@
     <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="10.0.0" />
     <PackageReference Include="Microsoft.Extensions.Logging" Version="10.0.0" />
     <PackageReference Include="Microsoft.Extensions.TimeProvider.Testing" Version="10.9.0" />
+    <PackageReference Include="Microsoft.AspNetCore.TestHost" Version="10.0.0" />
+    <FrameworkReference Include="Microsoft.AspNetCore.App" />
   </ItemGroup>
   <ItemGroup>
     <None Include="ClaudeCode/Fixtures/*" CopyToOutputDirectory="PreserveNewest" />
@@ -18,6 +20,8 @@
   <ItemGroup>
     <ProjectReference Include="../../src/Volcanic.AgenticCore/Volcanic.AgenticCore.csproj" />
     <ProjectReference Include="../../src/Volcanic.AgenticCore.Abstractions/Volcanic.AgenticCore.Abstractions.csproj" />
+    <ProjectReference Include="../../extensions/Volcanic.AgenticCore.Extensions.A2A/Volcanic.AgenticCore.Extensions.A2A.csproj" />
+    <ProjectReference Include="../../src/Volcanic.AgenticCore.A2A.Server/Volcanic.AgenticCore.A2A.Server.csproj" />
     <ProjectReference Include="../../extensions/Volcanic.AgenticCore.Extensions.Anthropic/Volcanic.AgenticCore.Extensions.Anthropic.csproj" />
     <ProjectReference Include="../../extensions/Volcanic.AgenticCore.Extensions.OpenAI/Volcanic.AgenticCore.Extensions.OpenAI.csproj" />
     <ProjectReference Include="../../extensions/Volcanic.AgenticCore.Extensions.ClaudeCode/Volcanic.AgenticCore.Extensions.ClaudeCode.csproj" />
@@ -27,4 +31,12 @@
     <ProjectReference Include="../../extensions/Volcanic.AgenticCore.Extensions.Scheduler/Volcanic.AgenticCore.Extensions.Scheduler.csproj" />
     <ProjectReference Include="../Volcanic.AgenticCore.Extensions.Tests.FakeMcpServer/Volcanic.AgenticCore.Extensions.Tests.FakeMcpServer.csproj" />
   </ItemGroup>
+  <!-- The ASP.NET shared framework (FrameworkReference above) makes the SDK skip copying Microsoft.Extensions.* assemblies,
+       but the fake MCP server runs on Microsoft.NETCore.App only and needs its own copies next to its dll. -->
+  <Target Name="CopyFakeMcpServerFrameworkAssemblies" AfterTargets="Build">
+    <ItemGroup>
+      <FakeMcpExtraDll Include="$(MSBuildProjectDirectory)/../Volcanic.AgenticCore.Extensions.Tests.FakeMcpServer/bin/$(Configuration)/$(TargetFramework)/Microsoft.Extensions.*.dll" />
+    </ItemGroup>
+    <Copy SourceFiles="@(FakeMcpExtraDll)" DestinationFolder="$(OutDir)" SkipUnchangedFiles="true" />
+  </Target>
 </Project>