Implement StreamableHTTP transport

Co-authored-by: Topher Bullock <topher.bullock@shopify.com>

lib/mcp/server.rb

@@ -24,7 +24,7 @@ module MCP
     include Instrumentation
 
     attr_writer :capabilities
-    attr_accessor :name, :version, :tools, :prompts, :resources, :server_context, :configuration
+    attr_accessor :name, :version, :tools, :prompts, :resources, :server_context, :configuration, :transport
 
     def initialize(
       name: "model_context_protocol",
@@ -35,7 +35,8 @@ module MCP
       resource_templates: [],
       server_context: nil,
       configuration: nil,
-      capabilities: nil
+      capabilities: nil,
+      transport: nil
     )
       @name = name
       @version = version
@@ -68,6 +69,7 @@ module MCP
         Methods::COMPLETION_COMPLETE => ->(_) {},
         Methods::LOGGING_SET_LEVEL => ->(_) {},
       }
+      @transport = transport
     end
 
     def capabilities
@@ -96,6 +98,14 @@ module MCP
       @prompts[prompt.name_value] = prompt
     end
 
+    def handle_rack_request(request)
+      @transport.handle_request(request)
+    end
+
+    def close
+      @transport.close
+    end
+
     def resources_list_handler(&block)
       @capabilities.support_resources
       @handlers[Methods::RESOURCES_LIST] = block