fix: Broken MCP works again (fixes #1862)

[vorburger]

Fixes #1862.

See also modelcontextprotocol/java-sdk#605.

[gemini-code-assist]

Summary of Changes

Hello @vorburger, 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 resolves a critical issue that was causing the Model Context Protocol (MCP) functionality to be broken. The core of the fix involves a significant refactoring of how JSON serialization and deserialization are managed. By centralizing the McpJsonMapper within the McpLoader, the changes abstract away specific implementation details, making the system more robust and easier to maintain. This ensures that all MCP operations now correctly handle JSON data, restoring full functionality.

Highlights

• Centralized JSON Mapper: The creation and provision of the McpJsonMapper have been centralized within the McpLoader class, introducing a new mcpJsonMapper() method.
• Reduced Direct Dependencies: Direct dependencies on JacksonMcpJsonMapper and ObjectMappers have been removed from McpLoader and CallToolCommand, promoting a more abstract and maintainable approach to JSON handling.
• Refactored Client Transport: The StdioClientTransport now utilizes the centralized mcpJsonMapper() method for its JSON mapping needs, ensuring consistent behavior.

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[gemini-code-assist]

Code Review

This pull request fixes an issue with the Model Context Protocol (MCP) by refactoring how the McpJsonMapper is obtained. The changes centralize the creation of the mapper into a new mcpJsonMapper() method in McpLoader, which is then used in both McpLoader and CallToolCommand. This removes a direct dependency on JacksonMcpJsonMapper and simplifies the code. The changes are correct and address the issue. I've suggested a minor improvement to make the new helper method static as it doesn't depend on instance state, which is a good practice for utility methods. This would require a corresponding change in the calling code.