Problem with flash in Hanami

flash_test.rb

require 'bundler/inline'

gemfile do
  gem 'hanami',       '~> 1.3'
end

require 'hanami/action/session'

module Home
  class Index
    include Hanami::Action
    include Hanami::Action::Session

    def call(_params)
      flash[:errors] = 'WRONG!'
      puts "In index"
      p flash
      redirect_to '/redirected'
    end
  end

  class Redirected
    include Hanami::Action
    include Hanami::Action::Session

    def call(_params)
      puts "In redirected"
      p flash
      self.body = flash[:errors]
    end
  end
end

module FlashApp
  class Application
    attr_reader :routes
    def initialize
      @routes = Hanami::Router.new do
        get '/', to: 'home#index'
        get '/redirected', to: 'home#redirected'
      end
    end
  end
end

app = Rack::Builder.new do
  use Rack::Session::Cookie, secret: SecureRandom.hex(16)
  run FlashApp::Application.new.routes
end

Rack::Server.start app: app

run.sh

curl -L localhost:8080

Result:

[2019-01-25 09:41:14] INFO  WEBrick 1.4.2
[2019-01-25 09:41:14] INFO  ruby 2.5.1 (2018-03-29) [x86_64-linux]
[2019-01-25 09:41:14] INFO  WEBrick::HTTPServer#start: pid=15276 port=8080
In index
#<Hanami::Action::Flash:0x560d5caf45a0 {:data=>{:errors=>"WRONG!"}, :kept=>{}} >
::1 - - [25/Jan/2019:09:41:17 CET] "GET / HTTP/1.1" 302 5
- -> /
In redirected
#<Hanami::Action::Flash:0x560d5cad21a8 {:data=>{}, :kept=>{}} >
::1 - - [25/Jan/2019:09:41:17 CET] "GET /redirected HTTP/1.1" 200 0
- -> /redirected