#287

backend/app/models/tag.rb

@@ -1,8 +1,12 @@
 class Tag < ApplicationRecord
+  include Discard::Model
+
   class NicoTagNormalisationError < ArgumentError
     ;
   end
 
+  default_scope -> { kept }
+
   has_many :post_tags, inverse_of: :tag
   has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :tag
   has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
@@ -160,7 +164,7 @@ class Tag < ApplicationRecord
         end
 
         tag_name = st.tag_name
-        st.destroy!
+        st.discard!
         tag_name.reload
         tag_name.update!(canonical: target_tag.tag_name)
       end