related tags: eliminate recent_tags cookie (#3955).

app/logical/related_tag_query.rb

@@ -26,6 +26,17 @@ class RelatedTagQuery
     end
   end
 
+  # Returns the top 20 most frequently added tags within the last 20 edits made by the user in the last hour.
+  def recent_tags(since: 1.hour.ago, max_edits: 20, max_tags: 20)
+    return [] unless user.present? && PostArchive.enabled?
+
+    versions = PostArchive.where(updater_id: user.id).where("updated_at > ?", since).order(id: :desc).limit(max_edits)
+    tags = versions.flat_map { |v| v.diff[:added_tags] }
+    tags = tags.reject { |tag| Tag.is_metatag?(tag) }
+    tags = tags.group_by(&:itself).transform_values(&:size).sort_by { |tag, count| [-count, tag] }.map(&:first)
+    tags.take(max_tags)
+  end
+
   def favorite_tags
     user&.favorite_tags.to_s.split
   end