Wire up real Live Preview for block-driven PDPs

Products.ts's admin.livePreview (added earlier this session) only made
the admin UI show a preview iframe — the actual page had no mechanism
to receive postMessage updates and re-render with unsaved draft data,
unlike Pages/Posts which already have this (LivePageContent.tsx/
LivePostContent.tsx). Edits in the backend were invisible in the
preview until an actual save (reported 2026-08-30).

New LiveProductContent.tsx mirrors LivePageContent.tsx's pattern
exactly: useLivePreview<PayloadProduct> + mapPayloadProduct, rendering
via ProductBlocks.tsx's now-exported renderProductBlock (sync) instead
of the full async ProductBlocks wrapper. testimonialsRef/crossSell
skipped in the live subset (need an async fetch a client component
can't perform inline) — same "editable subset only" scope Pages/Posts
already accept. shipping/tax/Kleinunternehmer context is fetched once
via the newly-exported getProductBlockContext() and passed in rather
than re-fetched per keystroke.

/der-eine and /tasse-die-pause now check draftMode() and swap in
LiveProductContent instead of the normal async ProductBlocks when
Payload's Live Preview iframe has it enabled.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013Eg6h91yngXmSnM51wxXM8

app/components/LiveProductContent.tsx

@@ -0,0 +1,36 @@
+"use client";
+
+import { useLivePreview } from "@payloadcms/live-preview-react";
+import { renderProductBlock, type ProductBlockContext } from "./ProductBlocks";
+import { mapPayloadProduct, type PayloadProduct, type Product } from "../lib/payload";
+
+const PAYLOAD_URL = process.env.NEXT_PUBLIC_PAYLOAD_URL || "https://payload.mk360.de";
+
+// Live-previewable subset of a Products document's `layout` — same
+// "editable subset only" scope as LivePageContent.tsx/LivePostContent.tsx:
+// `testimonialsRef` and `crossSell` are skipped here (both need an async
+// fetch a client component can't perform inline — testimonialsRef isn't
+// even registered on Products.layout anymore, kept out of the switch for
+// the same reason; crossSell's related-product card just doesn't update
+// live, shows correctly once saved and reloaded outside the iframe).
+// shipping/tax/Kleinunternehmer are passed in once from the server page
+// component instead of re-fetched on every keystroke — see
+// getProductBlockContext's own comment.
+export function LiveProductContent({
+  initialProduct,
+  shipping,
+  taxRate,
+  kleinunternehmer,
+}: {
+  initialProduct: Product;
+} & Omit<ProductBlockContext, "product">) {
+  const { data } = useLivePreview<PayloadProduct>({
+    initialData: initialProduct as unknown as PayloadProduct,
+    serverURL: PAYLOAD_URL,
+    depth: 2,
+  });
+  const product = data?.slug ? mapPayloadProduct(data) : initialProduct;
+  const ctx: ProductBlockContext = { product, shipping, taxRate, kleinunternehmer };
+
+  return <>{product.layout.map((block) => <div key={block.id}>{renderProductBlock(block, ctx)}</div>)}</>;
+}

app/components/ProductBlocks.tsx

@@ -30,12 +30,7 @@ import { TestimonialsGrid } from "./TestimonialsGrid";
 // need the live product/shipping/tax context that a generic content page
 // doesn't have.
 export async function ProductBlocks({ product }: { product: Product }) {
-  const [shipping, defaultTaxRate, kleinunternehmer] = await Promise.all([
-    getShippingSettings(),
-    getDefaultTaxRatePercent(),
-    getKleinunternehmer(),
-  ]);
-  const ctx: ProductBlockContext = { product, shipping, taxRate: effectiveTaxRate(product, defaultTaxRate), kleinunternehmer };
+  const ctx = await getProductBlockContext(product);
 
   const rendered = await Promise.all(
     product.layout.map(async (block) => {
@@ -114,14 +109,28 @@ export async function ProductBlocks({ product }: { product: Product }) {
   return <>{rendered}</>;
 }
 
-type ProductBlockContext = {
+export type ProductBlockContext = {
   product: Product;
   shipping: Awaited<ReturnType<typeof getShippingSettings>>;
   taxRate: number;
   kleinunternehmer: boolean;
 };
 
-function renderProductBlock(block: ProductBlock, ctx: ProductBlockContext): React.ReactNode {
+// Split out so LiveProductContent.tsx (the "use client" live-preview
+// counterpart, same pattern as LivePageContent.tsx/renderPageBlockSync)
+// can fetch this once itself instead of duplicating the three calls —
+// shipping/tax/Kleinunternehmer status essentially never change between
+// keystrokes in a preview session, unlike the product doc itself.
+export async function getProductBlockContext(product: Product): Promise<ProductBlockContext> {
+  const [shipping, defaultTaxRate, kleinunternehmer] = await Promise.all([
+    getShippingSettings(),
+    getDefaultTaxRatePercent(),
+    getKleinunternehmer(),
+  ]);
+  return { product, shipping, taxRate: effectiveTaxRate(product, defaultTaxRate), kleinunternehmer };
+}
+
+export function renderProductBlock(block: ProductBlock, ctx: ProductBlockContext): React.ReactNode {
   switch (block.blockType) {
     case "productHero":
       return <ProductHero {...ctx} body={block.body} />;