```ruby
module BlocklyInterpreter
  class Engine < ::Rails::Engine
    engine_name 'blockly_interpreter'
    isolate_namespace BlocklyInterpreter

    config.autoload_paths += Dir["#{config.root}/lib/**/"]
  end
end
```

Add lib directory to `config.eager_load_paths` as well as `config.autoload_paths`.
user
```ruby
module BlocklyInterpreter
  class Engine < ::Rails::Engine
    engine_name 'blockly_interpreter'
    isolate_namespace BlocklyInterpreter

    config.autoload_paths += Dir["#{config.root}/lib/**/"]
    config.eager_load_paths += Dir["#{config.root}/lib/**/"]
  end
end
```
assistant