Build it: Sync vs Async
An interactive sandbox where you drag real components together, connect them, and run a live traffic simulation to see where the design breaks.
Challenge: The web app gets 60 requests per second. Each request also has to do something slow like sending an email or generating a PDF. Do not make the user wait. Drop the slow work into a <strong>queue</strong> and let <strong>workers</strong> handle it in the background.