Why (iOS suspends the WebView mid-turn), the shape (API on lith, a Mongo queue, stateless workers, the thread socket and push as the return path), painting without a browser (graph.mjs in a worker-thread isolate, as the KidLisp conformance suite already does), the scale budget for 100 people at once, the container and where it runs, failure modes decided up front, what the phone keeps, and six slices with acceptance checks.