Support migration output messages containing multibyte characters

lib/ruby_lsp/ruby_lsp_rails/runner_client.rb

@@ -281,7 +281,7 @@ def send_message(request, **params)
         json = message.to_json
 
         @mutex.synchronize do
-          @stdin.write("Content-Length: #{json.length}\r\n\r\n", json)
+          @stdin.write("Content-Length: #{json.bytesize}\r\n\r\n", json)
         end
       rescue Errno::EPIPE
         # The server connection died

lib/ruby_lsp/ruby_lsp_rails/server.rb

@@ -13,7 +13,7 @@ module Common
       # Write a message to the client. Can be used for sending notifications to the editor
       def send_message(message)
         json_message = message.to_json
-        @stdout.write("Content-Length: #{json_message.length}\r\n\r\n#{json_message}")
+        @stdout.write("Content-Length: #{json_message.bytesize}\r\n\r\n#{json_message}")
       end
 
       # Log a message to the editor's output panel

test/ruby_lsp_rails/server_test.rb

@@ -217,6 +217,18 @@ def resolve_route_info(requirements)
     )
   end
 
+  test "send_message uses bytesize for content length with ASCII characters" do
+    @server.send(:send_message, { test: "hello" })
+    assert_equal "Content-Length: 16\r\n\r\n{\"test\":\"hello\"}", @stdout.string
+  end
+
+  test "send_message uses bytesize for content length with multibyte characters" do
+    @server.send(:send_message, { test: "こんにちは" }) # Japanese "hello"
+    expected = "Content-Length: 26\r\n\r\n"
+    expected += { test: "こんにちは" }.to_json.force_encoding(Encoding::ASCII_8BIT)
+    assert_equal expected, @stdout.string
+  end
+
   private
 
   def response