Ruby on Rails, Angularjs: Session getting reset

I am changing the value in session in an api controller, but it doesn't reflect next time the value of that variable in session is fetched. Here is the api-controller...

module Api
    module V0
        class RecommendationsApiController < ApplicationController

           def x
              r1 = session[:last_id]
              r2 = some_function(r1)
              session[:last_id] = r2 
              #doesn't reflect in the session next time this same function is called, and the old value is shown
              #though checking the value of session at this point shows the right value been set in the @delegate part of the session

           end
        end
    end
end

this is the session_store.rb

Application.config.session_store :cookie_store, key: '_session_name'

application_controller.rb

  protect_from_forgery

  after_filter :set_csrf_cookie_for_ng

  def set_csrf_cookie_for_ng
    cookies['XSRF-TOKEN'] = form_authenticity_token if protect_against_forgery?
  end

  protected

  def verified_request?
    super || form_authenticity_token == request.headers['X-XSRF-TOKEN']
  end

this is websiteApp.run function.

var csrf_token = $cookies['XSRF-TOKEN'];
$http.defaults.headers.common['X-XSRF-TOKEN'] = csrf_token;

I tried to set the token inside config, but config block doesn't have $cookies. So tried to set headers inside run.

Please help out.