.NET: Add CreateSessionAsync overload with taskId for A2AAgent session resumption

dotnet/src/Microsoft.Agents.AI.A2A/A2AAgent.cs

@@ -63,7 +63,16 @@ protected sealed override ValueTask<AgentSession> CreateSessionCoreAsync(Cancell
     /// <param name="contextId">The context id to continue.</param>
     /// <returns>A value task representing the asynchronous operation. The task result contains a new <see cref="AgentSession"/> instance.</returns>
     public ValueTask<AgentSession> CreateSessionAsync(string contextId)
-        => new(new A2AAgentSession() { ContextId = contextId });
+        => new(new A2AAgentSession() { ContextId = Throw.IfNullOrWhitespace(contextId) });
+
+    /// <summary>
+    /// Get a new <see cref="AgentSession"/> instance using an existing context id and task id, to resume that conversation from a specific task.
+    /// </summary>
+    /// <param name="contextId">The context id to continue.</param>
+    /// <param name="taskId">The task id to resume from.</param>
+    /// <returns>A value task representing the asynchronous operation. The task result contains a new <see cref="AgentSession"/> instance.</returns>
+    public ValueTask<AgentSession> CreateSessionAsync(string contextId, string taskId)
+        => new(new A2AAgentSession() { ContextId = Throw.IfNullOrWhitespace(contextId), TaskId = Throw.IfNullOrWhitespace(taskId) });
 
     /// <inheritdoc/>
     protected override ValueTask<JsonElement> SerializeSessionCoreAsync(AgentSession session, JsonSerializerOptions? jsonSerializerOptions = null, CancellationToken cancellationToken = default)

dotnet/tests/Microsoft.Agents.AI.A2A.UnitTests/A2AAgentTests.cs

@@ -1146,6 +1146,100 @@ public void GetService_RequestingAIAgentMetadata_ReturnsConsistentMetadata()
         Assert.Equal("a2a", metadata.ProviderName);
     }
 
+    /// <summary>
+    /// Verify that CreateSessionAsync with contextId creates a session with the correct context ID.
+    /// </summary>
+    [Fact]
+    public async Task CreateSessionAsync_WithContextId_CreatesSessionWithContextIdAsync()
+    {
+        // Arrange
+        const string ContextId = "test-context-123";
+
+        // Act
+        var session = await this._agent.CreateSessionAsync(ContextId);
+
+        // Assert
+        Assert.NotNull(session);
+        Assert.IsType<A2AAgentSession>(session);
+        var typedSession = (A2AAgentSession)session;
+        Assert.Equal(ContextId, typedSession.ContextId);
+        Assert.Null(typedSession.TaskId);
+    }
+
+    /// <summary>
+    /// Verify that CreateSessionAsync with contextId and taskId creates a session with both IDs set correctly.
+    /// </summary>
+    [Fact]
+    public async Task CreateSessionAsync_WithContextIdAndTaskId_CreatesSessionWithBothIdsAsync()
+    {
+        // Arrange
+        const string ContextId = "test-context-456";
+        const string TaskId = "test-task-789";
+
+        // Act
+        var session = await this._agent.CreateSessionAsync(ContextId, TaskId);
+
+        // Assert
+        Assert.NotNull(session);
+        Assert.IsType<A2AAgentSession>(session);
+        var typedSession = (A2AAgentSession)session;
+        Assert.Equal(ContextId, typedSession.ContextId);
+        Assert.Equal(TaskId, typedSession.TaskId);
+    }
+
+    /// <summary>
+    /// Verify that CreateSessionAsync throws when contextId is null, empty, or whitespace.
+    /// </summary>
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData(" ")]
+    [InlineData("\t")]
+    [InlineData("\r\n")]
+    public async Task CreateSessionAsync_WithInvalidContextId_ThrowsArgumentExceptionAsync(string? contextId)
+    {
+        // Act & Assert
+        await Assert.ThrowsAnyAsync<ArgumentException>(async () =>
+            await this._agent.CreateSessionAsync(contextId!));
+    }
+
+    /// <summary>
+    /// Verify that CreateSessionAsync with both parameters throws when contextId is null, empty, or whitespace.
+    /// </summary>
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData(" ")]
+    [InlineData("\t")]
+    [InlineData("\r\n")]
+    public async Task CreateSessionAsync_WithInvalidContextIdAndValidTaskId_ThrowsArgumentExceptionAsync(string? contextId)
+    {
+        // Arrange
+        const string TaskId = "valid-task-id";
+
+        // Act & Assert
+        await Assert.ThrowsAnyAsync<ArgumentException>(async () =>
+            await this._agent.CreateSessionAsync(contextId!, TaskId));
+    }
+
+    /// <summary>
+    /// Verify that CreateSessionAsync with both parameters throws when taskId is null, empty, or whitespace.
+    /// </summary>
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData(" ")]
+    [InlineData("\t")]
+    [InlineData("\r\n")]
+    public async Task CreateSessionAsync_WithValidContextIdAndInvalidTaskId_ThrowsArgumentExceptionAsync(string? taskId)
+    {
+        // Arrange
+        const string ContextId = "valid-context-id";
+
+        // Act & Assert
+        await Assert.ThrowsAnyAsync<ArgumentException>(async () =>
+            await this._agent.CreateSessionAsync(ContextId, taskId!));
+    }
     #endregion
 
     public void Dispose()