#125

backend/app/models/tag.rb

@@ -1,4 +1,8 @@
 class Tag < ApplicationRecord
+  class NicoTagNormalisationError < StandardError
+    ;
+  end
+
   has_many :post_tags, dependent: :delete_all, 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'
@@ -65,6 +69,8 @@ class Tag < ApplicationRecord
 
   def self.normalise_tags tag_names, with_tagme: true
     tags = tag_names.map do |name|
+      raise NicoTagNormalisationError if name.start_with?('nico:')
+
       pf, cat = CATEGORY_PREFIXES.find { |p, _| name.start_with?(p) } || ['', nil]
       name.delete_prefix!(pf)
       find_or_create_by_tag_name!(name, category: (cat || 'general')).tap do |tag|