Add client conformance tests and fix SSE parser require

Add conformance/client.rb for running MCP client conformance scenarios
(initialize, tools_call). Require event_stream_parser in http.rb so SSE
responses from the conformance server are parsed correctly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: atesgoral

conformance/client.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+# Conformance test client for MCP client testing.
+#
+# Usage: ruby conformance/client.rb <server-url>
+#
+# The scenario name is read from the MCP_CONFORMANCE_SCENARIO environment variable,
+# which is set by the conformance test runner.
+
+$LOAD_PATH.unshift(File.expand_path("../lib", __dir__))
+require "mcp"
+require "mcp/client"
+require "mcp/client/http"
+
+server_url = ARGV[0]
+scenario = ENV["MCP_CONFORMANCE_SCENARIO"]
+
+unless server_url && scenario
+  warn "Usage: MCP_CONFORMANCE_SCENARIO=<scenario> ruby conformance/client.rb <server-url>"
+  exit 1
+end
+
+transport = MCP::Client::HTTP.new(url: server_url)
+client = MCP::Client.new(transport: transport)
+
+case scenario
+when "initialize"
+  client.connect(client_info: { name: "ruby-conformance-client", version: "1.0.0" })
+  client.tools
+  client.close
+when "tools_call"
+  client.connect(client_info: { name: "ruby-conformance-client", version: "1.0.0" })
+  tools = client.tools
+  tool = tools.find { |t| t.name == "add_numbers" }
+  if tool
+    client.call_tool(tool: tool, arguments: { a: 1, b: 2 })
+  end
+  client.close
+else
+  warn "Unknown scenario: #{scenario}"
+  exit 1
+end

lib/mcp/client/http.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "event_stream_parser"
+
 module MCP
   class Client
     # TODO: HTTP GET for SSE streaming is not yet implemented.