Fix avatar and profile header descriptions not being serialized over ActivityPub (#39352)

app/serializers/activitypub/actor_serializer.rb

@@ -44,6 +44,16 @@ class ActivityPub::ActorSerializer < ActivityPub::Serializer
     end
   end
 
+  class ImageWithDescription < SimpleDelegator
+    attr_reader :description
+
+    def initialize(object, description)
+      super(object)
+
+      @description = description
+    end
+  end
+
   has_one :endpoints, serializer: EndpointsSerializer
 
   has_one :icon,  serializer: ActivityPub::ImageSerializer, if: :avatar_exists?
@@ -120,11 +130,11 @@ class ActivityPub::ActorSerializer < ActivityPub::Serializer
   end
 
   def icon
-    object.avatar
+    ImageWithDescription.new(object.avatar, object.avatar_description)
   end
 
   def image
-    object.header
+    ImageWithDescription.new(object.header, object.header_description)
   end
 
   def public_key

app/serializers/activitypub/image_serializer.rb

@@ -7,6 +7,7 @@ class ActivityPub::ImageSerializer < ActivityPub::Serializer
 
   attributes :type, :media_type, :url
   attribute :focal_point, if: :focal_point?
+  attribute :summary, if: :summary?
 
   def type
     'Image'
@@ -27,4 +28,12 @@ class ActivityPub::ImageSerializer < ActivityPub::Serializer
   def focal_point
     [object.meta['focus']['x'], object.meta['focus']['y']]
   end
+
+  def summary?
+    object.respond_to?(:description) && object.description.present?
+  end
+
+  def summary
+    object.description
+  end
 end