Fix processing of compacted single-item JSON-LD collections (#28816)

spec/services/activitypub/fetch_replies_service_spec.rb

@@ -34,6 +34,18 @@ RSpec.describe ActivityPub::FetchRepliesService, type: :service do
 
   describe '#call' do
     context 'when the payload is a Collection with inlined replies' do
+      context 'when there is a single reply, with the array compacted away' do
+        let(:items) { 'http://example.com/self-reply-1' }
+
+        it 'queues the expected worker' do
+          allow(FetchReplyWorker).to receive(:push_bulk)
+
+          subject.call(status, payload)
+
+          expect(FetchReplyWorker).to have_received(:push_bulk).with(['http://example.com/self-reply-1'])
+        end
+      end
+
       context 'when passing the collection itself' do
         it 'spawns workers for up to 5 replies on the same server' do
           allow(FetchReplyWorker).to receive(:push_bulk)