Fixes #3984 - Mention history does not show properly who got added.

app/assets/javascripts/app/controllers/_application_controller/_modal_generic_history.coffee

@@ -100,7 +100,7 @@ class App.GenericHistory extends App.ControllerModal
           content += " '#{ @translateItemValue(item, item.value_from) }'"
 
         if item.value_to
-          if item.value_from
+          if item.value_from || item.object is 'Mention'
             content += ' →'
           content += " '#{ @translateItemValue(item, item.value_to) }'"
         else if item.value_from
@@ -114,6 +114,14 @@ class App.GenericHistory extends App.ControllerModal
     newItems
 
   translateItemValue: ({object, attribute}, value) ->
+    if object is 'Mention'
+      result = '-'
+      if value
+        user = App.User.find(value)
+        if user
+          result = user.displayName()
+      return result
+
     localAttribute = @objectAttribute(object, attribute)
     if localAttribute && localAttribute.tag is 'datetime'
       return App.i18n.translateTimestamp(value)

app/models/mention.rb

@@ -30,6 +30,7 @@ class Mention < ApplicationModel
     {
       related_o_id:           mentionable_id,
       related_history_object: mentionable_type,
+      value_to:               user.id,
     }
   end
 

spec/system/ticket/zoom_spec.rb

@@ -1381,6 +1381,7 @@ RSpec.describe 'Ticket zoom', type: :system do
     context 'when logged in as agent' do
       let(:ticket) { create(:ticket, group: Group.find_by(name: 'Users')) }
       let!(:other_agent) { create(:agent, groups: [Group.find_by(name: 'Users')]) }
+      let!(:admin) { User.find_by(email: 'admin@example.com') }
 
       it 'can subscribe and unsubscribe' do
         ensure_websocket do
@@ -1400,8 +1401,9 @@ RSpec.describe 'Ticket zoom', type: :system do
           # check history for mention entries
           click 'h2.sidebar-header-headline.js-headline'
           click 'li[data-type=ticket-history] a'
-          expect(page).to have_text('created Mention')
+          expect(page).to have_text("created Mention → '#{admin.firstname} #{admin.lastname}'")
-          expect(page).to have_text('removed Mention')
+          expect(page).to have_text("removed Mention → '#{admin.firstname} #{admin.lastname}'")
+          expect(page).to have_text("created Mention → '#{other_agent.firstname} #{other_agent.lastname}'")
         end
       end
     end