Two-way sync without maintaining state is indeed a complex problem. It is loosely a multi-master replication problem. Shameless plug : We built a multi-direct

Two-way sync without maintaining state is indeed a complex problem. It is loosely a multi-master replication problem. Shameless plug : We built a multi-directional sync engine and a company called Syncari around it to solve exactly this problem. And added data pipelines around it. Mostly meant for sales operations/marketing operations folks, self-service style.