Add worker queue to enable sending message from S -> C

lib/ruby_mcp/capabilities/prompts.rb

@@ -0,0 +1,14 @@
+module RubyMCP::Capabilities::Prompts
+  def add_prompt(...)
+    @prompts.add(...)
+
+    RubyMCP.logger.info(@transport)
+    send_prompts_list_changed if @transport
+  end
+
+  private
+
+  def send_prompts_list_changed
+    @transport.enqueue(jsonrpc: "2.0", method: "notifications/prompts/list_changed")
+  end
+end

lib/ruby_mcp/server.rb

@@ -1,6 +1,7 @@
 module RubyMCP
   class Server
     include Capabilities::Logging
+    include Capabilities::Prompts
 
     attr_reader :lifecycle, :prompts, :resources
 
@@ -21,17 +22,13 @@ def connect(transport)
       start_transport
     end
 
-    def add_prompt(...)
-      @prompts.add(...)
-    end
-
     def add_resource(...)
       @resources.add(...)
     end
 
     def send_message(message)
       RubyMCP.logger.debug "S -> C : #{message}"
-      @transport.send(message)
+      @transport.enqueue(message)
     end
 
     def answer(request, result)

lib/ruby_mcp/transport/stdio.rb

@@ -1,16 +1,21 @@
 module RubyMCP
   class Transport
     class Stdio < Transport
+      def initialize
+        @queue = Queue.new
+      end
+
       def start
         @running = true
+        start_message_worker
 
         while @running
           begin
             line = $stdin.gets
 
             break if line.nil?
 
-            @on_message.call(line.strip)
+            @queue << [ :incoming, line.strip ]
           rescue StandardError => e
             RubyMCP.logger.error("Exception: #{e}")
           end
@@ -19,15 +24,33 @@ def start
         @on_close.call
       end
 
-      def send(message)
-        $stdout.puts(JSON.generate(message))
-        $stdout.flush
+      def enqueue(message)
+        @queue << [ :outgoing, JSON.generate(message) ]
       end
 
 
       def on_close(&block)
         @on_close = block
       end
+
+      private
+
+      def start_message_worker
+        sleep 0.2
+        RubyMCP.logger.info("Starting worker thread")
+        @worker = Thread.new do
+          while @running
+            type, message = @queue.pop
+
+            if type == :incoming
+              @on_message.call(message)
+            else
+              $stdout.puts(message)
+              $stdout.flush
+            end
+          end
+        end
+      end
     end
   end
 end

lib/ruby_mcp/transport/test.rb

@@ -11,7 +11,7 @@ def start
     @running = true
   end
 
-  def send(message)
+  def enqueue(message)
     @responses << JSON.generate(message)
   end
 

test/capabilities/test_prompts_capability.rb

@@ -329,4 +329,43 @@ def test_prompt_get_missing_required_argument_with_multiple_required_args
       }
     )
   end
+
+  def test_adding_prompt_sends_prompts_list_changed
+    @server.add_prompt(
+      name: "refactor",
+      description: "Review this code",
+      arguments: [
+        {
+          name: "code",
+          description: "code to review",
+          required: true,
+          completions: ->(*) { [ "some", "completion", "value" ] }
+        },
+        {
+          name: "language",
+          description: "Programming language",
+          required: true,
+          completions: ->(*) { [ "some", "completion", "value" ] }
+        }
+      ],
+      result: ->() {
+        {
+          description: "demo",
+          messages: [
+            {
+              role: "user",
+              content: {
+                type: "text",
+                text: "demo"
+              }
+            }
+          ]
+        }
+      },
+    )
+
+    assert_last_response(
+      jsonrpc: "2.0", method: "notifications/prompts/list_changed"
+    )
+  end
 end