Cached frame, dynamic hole, resumed page

Cache serialization is an existing primitive, not the PPR mechanism. The dashed child slot is the cache component temporary-reference hole: non-serializable JSX children are passed through as references rather than becoming the cached layout value. PPR adds readiness tracking for cache fills and uses markDynamic to identify the request-time hole inside that slot.

const CachedLayout = createCachedComponent(Layout)
const CachedAsyncContent = createCachedComponent(AsyncContent)

async function DynamicContent({ url }) {
  await markDynamic() // hangs only while prerender context is active
  await delay(300)     // request-time work
  return <pre>Requested URL: {url.pathname}</pre>
}

The bridge: @vitejs/plugin-rsc/ssr createFromReadableStream() decodes either Flight stream into the React tree consumed by React DOM. RSC prerender() and React DOM prerender() share a name, but only the latter returns postponed state for resume().

The second pass is demo scaffolding, not a requirement. Because the readiness gate waits for every discovered cache fill to settle and gives React a retry turn before cutoff, the warmup already emits a valid partial Flight prelude that could feed React DOM directly, so the restart is not strictly necessary here. The demo still discards it and renders again so that cache discovery and shell capture read as separate stages, which mirrors production frameworks whose discovery pass genuinely lacks final-render semantics.

The choice of prerender() is incidental too. The warmup could instead drain a plain renderToReadableStream(), and a partial prelude can also come from a controlled renderToReadableStream() cutoff. Next.js and vinext even pick opposite arrangements, so Next.js produces its final RSC with renderToReadableStream() under staged cutoff, while vinext warms with renderToReadableStream() and captures its final Flight with prerender(). What is fundamental is the phased control (readiness, an intentional dynamic hole, and a cutoff), not the number of passes or the specific stream API.