Reactions reset entropy

app/models/concerns/mentions.rb

@@ -37,7 +37,7 @@ module Mentions
     end
 
     def mentionable_content_changed?
-      rich_text_associations.any? { send(it.name).body_previously_changed? }
+      rich_text_associations.any? { send(it.name)&.body_previously_changed? }
     end
 
     def create_mentions_later

app/models/reaction.rb

@@ -4,7 +4,14 @@ class Reaction < ApplicationRecord
 
   scope :ordered, -> { order(:created_at) }
 
+  after_create :register_card_activity
+
   def all_emoji?
     content.match? /\A(\p{Emoji_Presentation}|\p{Extended_Pictographic}|\uFE0F)+\z/u
   end
+
+  private
+    def register_card_activity
+      comment.card.touch_last_active_at
+    end
 end

test/models/reaction_test.rb

@@ -0,0 +1,13 @@
+require "test_helper"
+
+class ReactionTest < ActiveSupport::TestCase
+  setup do
+    Current.session = sessions(:david)
+  end
+
+  test "creating a reaction touches the card activity" do
+    assert_changes -> { cards(:logo).reload.last_active_at } do
+      comments(:logo_1).reactions.create!(content: "Nice!")
+    end
+  end
+end