Add experimental basic quote post authoring (#35355)

app/serializers/activitypub/note_serializer.rb

@@ -3,7 +3,7 @@
 class ActivityPub::NoteSerializer < ActivityPub::Serializer
   include FormattingHelper
 
-  context_extensions :atom_uri, :conversation, :sensitive, :voters_count
+  context_extensions :atom_uri, :conversation, :sensitive, :voters_count, :quotes
 
   attributes :id, :type, :summary,
              :in_reply_to, :published, :url,
@@ -30,6 +30,11 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
 
   attribute :voters_count, if: :poll_and_voters_count?
 
+  attribute :quote, if: :quote?
+  attribute :quote, key: :_misskey_quote, if: :quote?
+  attribute :quote, key: :quote_uri, if: :quote?
+  attribute :quote_authorization, if: :quote_authorization?
+
   def id
     ActivityPub::TagManager.instance.uri_for(object)
   end
@@ -194,6 +199,24 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
     object.preloadable_poll&.voters_count
   end
 
+  def quote?
+    object.quote&.present?
+  end
+
+  def quote_authorization?
+    object.quote&.approval_uri.present?
+  end
+
+  def quote
+    # TODO: handle inlining self-quotes
+    ActivityPub::TagManager.instance.uri_for(object.quote.quoted_status)
+  end
+
+  def quote_authorization
+    # TODO: approval of local quotes may work differently, perhaps?
+    object.quote.approval_uri
+  end
+
   class MediaAttachmentSerializer < ActivityPub::Serializer
     context_extensions :blurhash, :focal_point