Specific ToolNotFoundError for easier handling than ToolError in multi-tenant environments

Description

We are running a remote MCP server and we are seeing errors like:

mcp.server.fastmcp.exceptions.ToolError: Unknown tool: <unknown-tool-name>

I'm unsure why our users are trying to call our remote MCP server with the name of a tool that we don't manage. Regardless, we would like to handle these errors separately from a generic ToolError. For instance:

• ToolNotFoundError: user error that shouldn't alert us.
• ToolError: an error that could indicate an actual issue with our system that we should alert on and fix.

References

I couldn't find any issues related to this.

从 mcp.server.fastmcp.exceptions.ToolError 开始，追踪发出“Unknown tool.”的远程服务器路径。定义未知工具与其他工具失败之间的区别，然后验证调用方能够分别处理这两种情况；该 issue 未指定测试文件，因此请先找到相关的异常或服务器测试，再更改行为。