If a handler starts a sleep/human approval/RPC call, or so, then this timer/promise is persisted in Restate's journal. Restate does the waiting. The handler process itself can suspend (e.g. on a serverless function), and the bidirectional connection is closed. Once the timer fires/approval comes in, Restate re-invokes the service with the journal of previously completed steps, and the service can replay to the exact point in the code where it suspended and continue from there. Restate is like a DB for journals, so you can sleep for as long as needed, also months.

So you have fast persistence of events while a handler can make progress, and suspensions while waiting.