According to the reply I received from SIN customer service, I have to go outside to check in - but that seems to be a "canned reply". In any case, staying airside in transit when arriving at T4 seems to be challenging.
I am now planning to be prepared either way (whether able to do an online checkin with Jetstar and stay airside, or not). Will report here after the trip in case anyone else has a similar question.
Last edited by tr3k; Jul 8, 2019 at 1:56 pm