ensure unique recipients

app/views/submissions/_error.html.erb

@@ -0,0 +1,7 @@
+<div id="submitters_error">
+  <% if local_assigns[:error] %>
+    <div class="text-center text-red-500">
+      <%= local_assigns[:error] %>
+    </div>
+  <% end %>
+</div>

app/views/submissions/new.html.erb

@@ -28,6 +28,7 @@
     <div id="list" class="hidden">
       <%= render 'list_form', template: @template %>
     </div>
+    <%= render 'submissions/error' %>
   </div>
   <%= content_for(:modal_extra) %>
 <% end %>

app/views/templates_preferences/show.html.erb

@@ -335,6 +335,18 @@
           </div>
         <% end %>
       <% end %>
+      <% if can?(:manage, :personalization_advanced) %>
+        <%= form_for @template, url: template_preferences_path(@template), method: :post, html: { autocomplete: 'off', class: 'mt-2' }, data: { close_on_submit: false } do |f| %>
+          <div class="flex items-center mt-4 justify-between w-full">
+            <span>
+              <%= t('ensure_unique_recipients') %>
+            </span>
+            <%= f.fields_for :preferences, Struct.new(:validate_unique_submitters).new(@template.preferences['validate_unique_submitters']) do |ff| %>
+              <%= ff.check_box :validate_unique_submitters, { class: 'toggle', onchange: 'this.form.requestSubmit()' }, 'true', '' %>
+            <% end %>
+          </div>
+        <% end %>
+      <% end %>
       <div class="form-control mt-5 pb-2">
         <%= button_tag button_title(title: t('save'), disabled_with: t('updating')), class: 'base-button', form: :submitters_form %>
       </div>