More extensible CallToolRequest

Expected Behavior

We want to define our own tool-specific requests with own parsers for 'params'.

Current Behavior

The arguments for tool calls are always Maps.

Context

We develop our own MCP server that offers features like querying and we have our own set of tools to parse, validate and execute them.

The problem is that request object is always de-serialised as a map and we need to serialise it back or figure out a way to reconstruct our objects from the maps. It works most of the time, but is rather inconvenient for queries.

There is https://github.com/modelcontextprotocol/java-sdk/blob/main/mcp-core/src/main/java/io/modelcontextprotocol/json/McpJsonMapper.java, but as far as I understand, it is mainly used to decouple Jackson from the rest of the code.

We could have used that but it looks rather technical.

What I would like to have: some way to define my own request objects and make their payloads shallow or leave them unparsed so the each individual tool can later parse its payload and decide what to do. Or stick with standard map-based one if that is fine for it.

まず McpJsonMapper.java を読み、CallToolRequest がツール引数をどのようにデシリアライズするかを追跡します。既存の map ベースの動作を維持しながら、ツール固有のリクエスト解析でサポートされる拡張ポイントを定義し、関連するリクエストデシリアライズテストで選択した動作を検証します。