.NET: Support InvokeMcpTool for declarative workflows

[peibekwe]

Motivation and Context

This implementation supports the InvokeMcpTool action in a declarative workflow to call configured mcp servers directly from the workflow without going through an AI agent first. This is different from the standard InvokeAzureAgent pattern where the AI decides which functions to call based on the conversation.

Includes tests and samples for the new action type and sample yaml implementations.

Fixes #3415
Fixes #3738

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

Adds first-class support for invoking MCP (Model Context Protocol) server tools directly from .NET declarative workflows (without going through an AI agent tool-selection step), including approval handling, result parsing, integration tests, and a Getting Started sample.

Changes:

• Introduces InvokeMcpToolExecutor plus IMcpToolHandler and a DefaultMcpToolHandler implementation based on the MCP C# SDK.
• Wires MCP tool handling through workflow options and factory plumbing; adds workflow interpreter support for InvokeMcpTool.
• Adds unit + integration tests and a new declarative workflow sample demonstrating direct MCP tool invocation.

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/ObjectModel/InvokeMcpToolExecutor.cs	New executor implementing InvokeMcpTool execution + approval + output assignment.
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/IMcpToolHandler.cs	New abstraction for MCP tool invocation used by declarative workflows.
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/DefaultMcpToolHandler.cs	Default MCP SDK-based handler implementation with client caching and content mapping.
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/DeclarativeWorkflowOptions.cs	Adds McpToolHandler option to enable MCP tool invocation in workflows.
dotnet/src/Shared/Workflows/Execution/WorkflowFactory.cs	Plumbs McpToolHandler through factory-created workflow options.
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/Interpreter/WorkflowActionVisitor.cs	Adds interpreter support to build workflow graph nodes/ports for InvokeMcpTool (incl. approval flow).
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/Interpreter/WorkflowTemplateVisitor.cs	Marks InvokeMcpTool as not supported for template generation (consistent with other tool-invocation actions).
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/ObjectModel/InvokeFunctionToolExecutor.cs	Refactors array schema inference to use GetListTypeFromJson extension.
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/Extensions/JsonDocumentExtensions.cs	Adds GetListTypeFromJson and improves nested/empty-array parsing behavior.
dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/ObjectModel/InvokeMcpToolExecutorTest.cs	New unit tests covering InvokeMcpTool executor behavior and result parsing scenarios.
dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/Extensions/JsonDocumentExtensionsTests.cs	Adds tests for list-type inference from JSON arrays.
dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.IntegrationTests/Framework/IntegrationTest.cs	Extends test options creation to optionally provide an MCP tool handler.
dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.IntegrationTests/InvokeToolWorkflowTest.cs	New integration tests covering InvokeFunctionTool + InvokeMcpTool workflows and approval paths.
dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.IntegrationTests/InvokeFunctionToolWorkflowTest.cs	Removes older InvokeFunctionTool-only integration test (superseded by combined test).
dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.IntegrationTests/Workflows/InvokeMcpTool.yaml	New workflow YAML for invoking an MCP tool without approval.
dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.IntegrationTests/Workflows/InvokeMcpToolWithApproval.yaml	New workflow YAML for invoking an MCP tool with approval required.
dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/Microsoft.Agents.AI.Workflows.Declarative.csproj	Adds ModelContextProtocol package dependency for MCP support.
dotnet/Directory.Packages.props	Updates workflow-related package versions (and central MCP package version already present).
dotnet/samples/GettingStarted/Workflows/Declarative/InvokeMcpTool/Program.cs	New sample showing how to configure McpToolHandler and run an MCP-enabled workflow.
dotnet/samples/GettingStarted/Workflows/Declarative/InvokeMcpTool/InvokeMcpTool.yaml	New sample workflow chaining MCP calls and an agent summarization step.
dotnet/samples/GettingStarted/Workflows/Declarative/InvokeMcpTool/InvokeMcpTool.csproj	New sample project for the InvokeMcpTool workflow demo.
dotnet/agent-framework-dotnet.slnx	Adds the new InvokeMcpTool sample project to the solution.

Comments suppressed due to low confidence (2)

dotnet/samples/GettingStarted/Workflows/Declarative/InvokeMcpTool/Program.cs:63

• This sample's DefaultAzureCredential warning is less specific than the standard warning used elsewhere in the repo (latency, unintended credential probing, and security risks from fallback mechanisms). Consider aligning the comment text with the established wording so readers get consistent production guidance.

        // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
        DefaultAzureCredential credential = new();
        DefaultMcpToolHandler mcpToolHandler = new(

dotnet/samples/GettingStarted/Workflows/Declarative/InvokeMcpTool/Program.cs:121

• There is a second DefaultAzureCredential warning here that also doesn’t include the repo-standard details (latency, unintended credential probing, and security risks from fallback mechanisms). Consider using the same warning wording used in other GettingStarted samples for consistency.

        // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
        AIProjectClient aiProjectClient = new(foundryEndpoint, new DefaultAzureCredential());