POC: clientLoader.unstable_batch - batch clientLoader with single fetch server call

[brophdawg11]

POC for a new unstable_batch flag on clientLoader that allows a route's client loader to participate in the normal single fetch server request, rather than forcing a separate out-of-band server call.

export async function clientLoader({ serverLoader }: Route.ClientLoaderArgs) {
  const data = await serverLoader({ batch: true });
  // ... client-side augmentation ...
  return { ...data, extra: "client-only stuff" };
}

clientLoader.unstable_batch = true

With unstable_batch = true:

• The server loader call is initiated eagerly before clientLoader runs, as part of the normal single fetch request alongside all other loaders
• When the clientLoader calls serverLoader(), it awaits the already-in-flight batched response rather than issuing a new request

Known limitation: <Link prefetch>

<Link prefetch> still excludes routes with hasClientLoader from the prefetch .data URL on the first prefetch, even when unstable_batch = true because we don't have the route module to know if unstable_batch is set.

plan:

• we already do an AST parse at route module extraction for splitting loader/action/etc.
• move that up to manifest creation time and cache
• short circuit on quick regex for unstable_batch
• add clientLoaderBatch boolean to manifest

[github-actions]

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