feat(py): mcp sample v2

[MengqinShen]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @MengqinShen, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly refactors the Python MCP (Model Context Protocol) plugin, enhancing its integration with the Genkit framework. The changes introduce a more flexible and robust architecture for dynamic tool registration and improved resource management. A new sample application has been added to showcase these capabilities, providing practical examples of how to interact with various MCP servers and manage client connections. These updates aim to provide a more stable, feature-rich, and developer-friendly experience for integrating external tools and resources via MCP.

Highlights

• Improved Error Handling: Changed except Exception to except BaseException in core Genkit files (genkit/aio/loop.py and genkit/core/reflection.py) for more robust exception catching, including system-exiting exceptions.
• MCP Plugin Refactoring: The McpClient class has been refactored to no longer directly inherit from Plugin, instead interacting with GenkitRegistry. This includes removing old init, resolve, and list_actions methods and introducing initialize and resolve_action to align with the new plugin architecture. Connection and closure logic now uses AsyncExitStack for better resource management.
• Dynamic Tool Registration Enhancements: Tool names registered with Genkit from MCP are now formatted as server_name_tool_name (e.g., git-client_tool1) instead of using / to prevent potential issues. Input schemas from MCP tools are also now explicitly patched into the Genkit actions.
• MCP Host Capabilities: The McpHost class has been extended with new methods like reconnect, get_active_tools, and get_active_resources to provide more granular control and discovery mechanisms for connected MCP clients.
• Resource Handling Logic Updates: Adjustments were made to how resource content is processed and converted, ensuring proper handling of model_dump() for mcp.types.TextContent and explicit casting of URIs to AnyUrl for resource contents.
• New MCP Sample Application: A comprehensive new sample application (py/samples/mcp) has been added. It demonstrates various MCP client functionalities, including interaction with git and filesystem servers, dynamic client control (enable/disable/reconnect), and reading/updating files, complete with pyproject.toml, run.sh, and example server/client code.
• Dependency Management: Added structlog as a dependency for the MCP plugin and ty for development. The main pyproject.toml and uv.lock files have been updated to include the new genkit-plugins-mcp and mcp-sample projects and their dependencies.

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[gemini-code-assist]

Code Review

This pull request introduces a new MCP sample and significantly refactors the MCP client implementation. The refactoring of the McpClient is a notable improvement, particularly the fix for the late-binding closure issue when creating tool wrappers and the enhanced management of asynchronous contexts using AsyncExitStack. The new sample is comprehensive and provides good examples. However, there are a few critical issues to address. The use of except BaseException is dangerous and can lead to unexpected behavior, such as preventing the application from being terminated. Additionally, there's an instance of silently swallowing exceptions in the McpHost which should be fixed. I've also included some comments on code style and potential improvements.