"Internal error calling tool" following readme example

[thisismydesign]

Describe the bug

class ApplicationController < ActionController::API
  def mcp2
    server = MCP::Server.new(
        name: "rails-mcp",
        version: "1.0.0",
        tools: [SecretNumber]
      )
    render(json: server.handle_json(request.body.read))
  end
end

class SecretNumber < MCP::Tool
  class << self
    def call(message:, server_context:)
      MCP::Tool::Response.new([{
        type: "text",
        text: "1337",
      }])
    end
  end
end

MCP.configure do |config|
  config.exception_reporter = ->(exception, server_context) {
    Rails.logger.error "MCP exception: #{exception.class} - #{exception.message}"
    Rails.logger.error "Backtrace: #{exception.backtrace.join("\n")}"
  }
end

I can connect to the MCP from calude code, when it tries to call the tool:

Server:

MCP exception: MCP::Server::RequestHandlerError - Internal error calling tool secret_number
Backtrace: /usr/local/bundle/gems/mcp-0.4.0/lib/mcp/server.rb:291:in 'MCP::Server#call_tool'
/usr/local/bundle/gems/mcp-0.4.0/lib/mcp/server.rb:215:in 'Method#call'

Client:

> give me a secret number 

⏺ I'll use the secret number tool to get you a secret number.
  ⎿  Error: MCP error -32603: Internal error

⏺ I tried to use the mcp__test__secret_number tool, but it returned an internal error. This appears to be a test MCP server tool that may not be properly configured or
  running.

v0.4.0

[thisismydesign]

The underlying exception:

MCP exception: ArgumentError - wrong number of arguments (given 1, expected 2)
Backtrace: /app/app/controllers/application_controller.rb:29:in 'block in mcp2'
/usr/local/bundle/bundler/gems/ruby-sdk-da7603eb4d67/lib/mcp/server.rb:345:in 'MCP::Server#call_tool_with_args'
/usr/local/bundle/bundler/gems/ruby-sdk-da7603eb4d67/lib/mcp/server.rb:288:in 'MCP::Server#call_tool'
/usr/local/bundle/bundler/gems/ruby-sdk-da7603eb4d67/lib/mcp/server.rb:215:in 'Method#call'

Apparently this is incorrect:

define_tool() { |args, server_context| }

Instead:

define_tool() { |**args| }

[koic]

Yeah, As an example, the block arguments needed to be written as |args, server_context:|. I opened #187 to fix this.

[thisismydesign]

Thanks @koic. The class definition example doesn't work either..

Fails:

  def self.call(message:, server_context:)
    MCP::Tool::Response.new([{
      type: "text",
      text: "1337",
    }])
  end

  def self.call(message, server_context:)
    MCP::Tool::Response.new([{
      type: "text",
      text: "1337",
    }])
  end

Works:

  def self.call(**args)
    MCP::Tool::Response.new([{
      type: "text",
      text: "1337",
    }])
  end

[thisismydesign]

Nevermind, looks like self.call is passed the inputs defined in input_schema plus server_context.