Phase 3: wire e-invoice generation into checkout email + download routes

invoiceData.ts's generateInvoicePdf()/generateCorrectionInvoicePdf() now
call renderInvoiceEInvoice()/renderCorrectionInvoiceEInvoice() instead of
the plain PDF renderers — both are the single wrapper every caller
already goes through (orderEmail.ts's checkout attachment, and the two
on-demand /invoice and /correction-invoice download routes), so this one
change switches all three. Buffer.from() wraps the library's Uint8Array
return value — every downstream consumer already expects a Buffer,
unchanged.

Imports from "@einfach-produktiv/invoicing/einvoice" (a new subpath, not
the package's main entry) — @e-invoice-eu/core pulls in Node-only
dependencies that broke the client bundle when reachable from the main
entry, which a Client Component also imports transitively (Live
Preview). See that package's own commit for the fix.

Existing failure-handling is unchanged and covers this: a PDF-generation
error still doesn't block the confirmation email, it just sends without
the attachment and alerts admin (see orderEmail.ts) — same safety net
that already existed for the plain-PDF path.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/lib/invoiceData.ts

@@ -1,11 +1,17 @@
 import { getCompanySettings, type CompanySettings } from "./payload";
+// "/einvoice" subpath, not the package's main entry — @e-invoice-eu/core
+// pulls in Node-only dependencies that break a client bundle if reachable
+// from a Client Component; see that package's own src/index.ts comment.
+// This file is server-only (Next.js Server Components/Route Handlers),
+// but importing from the main entry would still poison the bundle for
+// any Client Component that transitively imports this same package.
 import {
-  renderInvoicePdf,
-  renderCorrectionInvoicePdf,
+  renderInvoiceEInvoice,
+  renderCorrectionInvoiceEInvoice,
   type InvoiceOrder,
   type CorrectionInvoiceKind,
   type CorrectionInvoiceOrder,
-} from "@einfach-produktiv/invoicing";
+} from "@einfach-produktiv/invoicing/einvoice";
 
 export type { CompanySettings };
 
@@ -24,18 +30,26 @@ export async function getSellerForInvoice(): Promise<CompanySettings | null> {
 // later always matches what they were emailed. `seller` is passed in
 // rather than fetched here, so a caller that already has it (see above)
 // doesn't fetch it twice.
+//
+// As of 2026-07-23 (e-invoicing Phase 3), this produces a Factur-X-EN16931
+// hybrid PDF/A-3 (visual PDF + embedded EN16931 XML) via
+// @einfach-produktiv/invoicing's renderInvoiceEInvoice(), not a plain PDF —
+// same visual document, but now machine-readable too. `Buffer.from()`
+// wraps the library's `Uint8Array` return value — every downstream
+// consumer (nodemailer's attachment `content`, the two on-demand download
+// routes) already expects a `Buffer`, unchanged by this switch.
 export async function generateInvoicePdf(order: InvoiceOrder, seller: CompanySettings | null): Promise<Buffer | null> {
   if (!seller) {
     console.error("generateInvoicePdf: no company-settings row found for tenant");
     return null;
   }
-  return renderInvoicePdf(order, seller);
+  return Buffer.from(await renderInvoiceEInvoice(order, seller));
 }
 
 // Frontend-side regeneration for the "Stornorechnung/Gutschrift
 // herunterladen" download button — the real document was already
 // generated once (Payload's Orders.ts afterChange hook) and emailed; this
-// reproduces the identical PDF from the order's own stored
+// reproduces the identical PDF/A-3+XML from the order's own stored
 // correctionInvoiceNumber/correctionInvoiceIssuedAt, same "deterministic
 // regeneration, not file storage" approach as the original invoice.
 export async function generateCorrectionInvoicePdf(
@@ -47,5 +61,5 @@ export async function generateCorrectionInvoicePdf(
     console.error("generateCorrectionInvoicePdf: no company-settings row found for tenant");
     return null;
   }
-  return renderCorrectionInvoicePdf(kind, order, seller);
+  return Buffer.from(await renderCorrectionInvoiceEInvoice(kind, order, seller));
 }