Use dossier_display_state helper

app/serializers/dossier_serializer.rb

@@ -1,4 +1,6 @@
 class DossierSerializer < ActiveModel::Serializer
+  include DossierHelper
+
   attributes :id,
     :created_at,
     :updated_at,
@@ -46,7 +48,7 @@ class DossierSerializer < ActiveModel::Serializer
   end
 
   def simplified_state
-    object.decorate.display_state
+    dossier_display_state(object)
   end
 
   def initiated_at

app/views/new_gestionnaire/dossiers/_header.html.haml

@@ -46,4 +46,4 @@
   .print-header
     = dossier.procedure.libelle.truncate_words(10)
     >
-    = "Dossier nº #{dossier.id} (#{dossier.statut})"
+    = "Dossier nº #{dossier.id} (#{dossier_display_state(dossier, lower: true)})"

app/views/new_gestionnaire/dossiers/_state_button.html.haml

@@ -1,7 +1,7 @@
 - if dossier.en_construction? || dossier.en_instruction?
   %span.dropdown
     %button.button.primary.dropdown-button
-      = dossier.decorate.display_state
+      = dossier_display_state dossier
     .dropdown-content.fade-in-down
       %ul.dropdown-items
         - if dossier.en_construction?
@@ -55,7 +55,7 @@
   - if dossier.motivation.present? || dossier.attestation.present?
     %span.dropdown
       %button.button.dropdown-button{ class: button_or_label_class(dossier) }
-        = dossier.statut
+        = dossier_display_state(dossier, lower: true)
       .dropdown-content.fade-in-down.terminated
         - if dossier.motivation.present?
           %h4 Motivation
@@ -67,4 +67,4 @@
           = link_to "Voir l'attestation", attestation_gestionnaire_dossier_path(dossier.procedure, dossier), target: '_blank', class: 'button'
   - else
     %span.label{ class: button_or_label_class(dossier) }
-      = dossier.statut
+      = dossier_display_state(dossier, lower: true)