# einfach-produktiv — Frontend

Next.js frontend for [einfach-produktiv.mk360.de](https://einfach-produktiv.mk360.de),
Coolify-managed and deployed from this repo (`git.mk360.de/Marco/einfach-produktiv`).
For the VPS-wide infrastructure this app runs on (Caddy, Coolify, Gitea, the
shared Payload instance), see `~/dev/README.md` — this file only covers what's
specific to this project.

## Stack

- **Next.js 16.2.9** (App Router, `output: "standalone"` for a small Docker
  image — see `AGENTS.md` before touching anything version-specific, this
  Next.js release differs from older training-data conventions)
- **React 19.2.4**, **Tailwind CSS 4**, **Motion** for animation
- **`@react-pdf/renderer`** for invoice PDF generation (see "Invoice
  PDFs" below) — no headless-browser dependency
- No local database — all editable content (and now orders/customer
  accounts) lives in the shared Payload CMS at `payload.mk360.de` (see
  below). Customer auth is Payload's own (a second, separate `auth: true`
  collection there, `customers` — not this app's own user store), bridged
  via an httpOnly session cookie this app mints itself; see "Orders &
  customer accounts" below.

## Shared modules

`@einfach-produktiv/invoicing` (a separate repo, consumed as a git
dependency — see "Invoice PDFs" below) is where framework-agnostic logic
shared with the Payload backend lives, so it's written once instead of
maintained as two independently-drifting copies. Beyond invoice/e-invoice
PDF generation and tax-breakdown math, it also holds VIES VAT-ID checking,
VAT-ID format validation, PLZ digit-count validation, and shipping-carrier
tracking-label logic — all previously hand-duplicated `app/lib/*.ts` files
in this repo, now imported from the shared package instead. See that
package's own README for what's in it and why each piece was unified.

## Getting started

```bash
npm install
npm run dev
```

Open [http://localhost:3000](http://localhost:3000). `npm run build && npm run
start` reproduces the production build locally — do this before pushing,
since Coolify builds with `--no-cache` and a failed build only surfaces there
otherwise.

**Environment variables:** `PAYLOAD_URL` (defaults to `https://payload.mk360.de`
if unset, see `app/lib/payload.ts`). `PAYLOAD_PREVIEW_SECRET` (no safe
default — required for Live Preview, see below; must match the value set on
the Payload backend). `NEXT_PUBLIC_PAYLOAD_URL` (optional, defaults to the
same `https://payload.mk360.de` — only needed if the client-side Live
Preview components should ever point somewhere else). `DISCOUNT_SERVICE_SECRET`
(no safe default — required for discount codes to validate/redeem at all;
must match the value set on the Payload backend). `ORDER_SERVICE_SECRET`
(no safe default — required for `/api/checkout` to persist an order in
Payload at all, for `/api/account/verify-email` to look up a customer
by their verification token, and for `getCompanySettings()` to read the
`company-settings` collection (seller data for invoice PDFs); must match
the value set on the Payload backend — also used there for the same
header). `SMTP_USER`/`SMTP_PASSWORD`
(no safe default — required for `app/lib/alertAdmin.ts`'s critical-failure
alerts and resend-verification emails; **does not** need to match anything
on the Payload side — this app's SMTP connection is deliberately
independent, see the "Monitoring & alerting" section). `STRIPE_SECRET_KEY`,
`STRIPE_WEBHOOK_SECRET`, `NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY`,
`PAYMENT_WEBHOOK_SECRET`, `PAYMENT_TEST_MODE` — see "Payment processing
(Stripe)" below. `BREVO_API_KEY`, `BREVO_LIST_ID`,
`BREVO_DOUBLE_OPTIN_TEMPLATE_ID` (no safe default — required for
newsletter signups to trigger a confirmation email at all),
`BREVO_DOI_REDIRECT_URL` (optional, defaults to `/newsletter-confirmed`) — see
"Newsletter signup" below. Set in Coolify's app settings for production,
not in a committed `.env`.

## Pages

| Route | Purpose |
|---|---|
| `/` | Home — hero, product spotlight, tools grid, trust row |
| `/shop` | Product grid (all active products for this tenant) |
| `/blog`, `/blog/[slug]` | Blog overview + post detail |
| `/cart` | Cart (localStorage-backed, see below) |
| `/checkout` | Shipping + payment method selection, order summary |
| `/bestellbestaetigung` | Order confirmation — reads the one-time snapshot `/checkout` wrote |
| `/konto/login`, `/konto/registrieren` | Customer login / standalone registration |
| `/konto/bestellungen`, `/konto/bestellungen/[orderNumber]` | Order history + order detail (own orders only) |
| `/konto/profil` | Profile/address editing + password change |
| `/konto/merkliste` | Wishlist (when `wishlistEnabled`, see "Feature toggles" below) |
| `/challenge` | "Mini-Challenge" tool |
| `/todo-cards` | "Todo-Karten" tool |
| `/die-sieben` | "Die Sieben" — free monthly ritual (evergreen concept page only; the WordPress original's monthly-changing edition/archive/template has no content model in this codebase yet, see `app/die-sieben/page.tsx`'s own comment) |
| `/newsletter` | Newsletter signup |
| `/versand` | Shipping policy (timeframes, costs) |
| `/impressum`, `/datenschutz`, `/agb`, `/widerruf` | Legal pages (from Payload, see `legal-pages` below) |

### Responsive design

The site uses a fluid, `clamp()`-based responsive system (`app/lib/fluid.ts`,
tokens hand-authored into `app/globals.css`'s `@theme`/`:root` blocks) that
scales continuously between a 640px floor and a 1440px ceiling — most
components need no structural breakpoint at all. Where a genuine
structural reflow is needed (grid-to-stack, flex-direction switches), the
site uses a single `sm:` (640px) breakpoint, with a documented handful of
exceptions still gated on `lg:` (1024px) for real fixed-width content:
the Cart/Checkout two-column split, the legal-page table-of-contents
sidebar, the newsletter/todo-cards hero and benefits sections,
`Footer.tsx`'s legal-links row, and `TrustRow.tsx`.

Below `lg:` (1024px), the Navbar's hamburger opens a fullscreen nav panel
(circular reveal animation, a sibling of `<header>` rather than a child so
the header's own `backdrop-blur` doesn't break the panel's
fixed-to-viewport positioning) instead of an inline dropdown; the
wishlist/search icons are hidden below `sm:` (640px) so Account + Cart
stay the only always-visible icons on narrow phones (see "Feature
toggles" below). `Navbar.tsx` itself keeps its own separate `md:`/`lg:`
3-tier scheme for its nav links — horizontal nav-link overflow is a
different failure mode than the vertical grid/flex reflows the rest of
the site handles with `sm:`.

### SEO & structured data

Every page can carry real per-page metadata — `/blog/[slug]`'s
`generateMetadata()` reads a post's own `seoTitle`/`seoDescription`/`seoImage`
(see the `posts` collection below); `app/layout.tsx`'s `generateMetadata()`
reads `getSeoSettings()` (ISR-cached, backed by `company-settings`) for
the site-wide fallback.

JSON-LD structured data (`app/lib/structuredData.ts`, no headless
external validation step, just direct grepping of the rendered
`application/ld+json` script) is emitted for the pages Google gives rich
results for: an `Organization` schema site-wide in the root layout (from
`getCompanySettings()`, excluding sensitive fields like `iban`/`bic`,
with a stable `@id` that other schemas link back to rather than repeating
the full object), a `Product` schema on `/todo-cards` (the one page with
its own dedicated single-product URL — deliberately not on `/shop`'s
grid, since most products there have no individual detail page to point
a `Product`'s `url` at), and a `BlogPosting` schema on every
`/blog/[slug]` page.

## Content backend: Payload CMS

This app is one **tenant** in a shared, multi-tenant Payload instance also
used by other projects on the same VPS (see `docker/payload/` in the infra
repo). All content queries go through `app/lib/payload.ts`, which hardcodes
`TENANT_SLUG = "einfach-produktiv"` and filters every request with
`where[tenant.slug][equals]=einfach-produktiv` — the tenant field itself is
injected automatically into every collection below by Payload's
`multiTenantPlugin`, not defined in this app.

`/api/products` is this app's own same-origin proxy route (`app/api/products/route.ts`)
in front of `getProducts()` — used by client components (cart, related
products) that need the catalog reactively, so they don't talk to Payload's
API directly and reuse Next.js's fetch cache instead of an extra round trip.

### Collections used by this tenant

Most reads are public (`access.read: () => true`); writes are always
admin-gated in the Payload admin UI at `payload.mk360.de/admin`. A growing
subset below is **not** public-read at all (`discount-codes`, `orders`,
`customers`, `number-ranges`, `company-settings`) — each row says so and
explains what does have access instead.

| Collection (slug) | Used for | Key fields |
|---|---|---|
| `products` | `/shop` grid, homepage spotlight, cart, checkout | `name`, `slug` (cart item id — **not** Payload's numeric id, so existing localStorage carts survive catalog changes), `description`, `price`, `compareAtPrice` (optional strikethrough), `image`, `detailHref`, `sortOrder`, `active` (hides a product from the shop grid/spotlight/related-products only — cart/checkout/its own detail page still resolve it regardless, see Discount codes section below for the same opt-in-filtering principle), `categories` (optional, `hasMany` relation to the backend's `product-categories` collection — own collection, not shared with blog's `categories`, so a "Karten" product category and a same-named blog category never collide; not required, so an untagged product still shows everywhere, just matches every `/shop` category filter instead of being excluded — see `Product.categories`' own comment in `lib/payload.ts`), `spotlight` + `spotlightEyebrow`/`spotlightHeadline`/`spotlightText`/`spotlightImage` (homepage "Neu im Shop" section — falls back to `image` if no dedicated spotlight image is set; forced onto the sole active product when exactly 1 exists, see `getSpotlightProduct()`), `taxRatePercent` (optional per-product VAT override, see "Product bundles & per-product tax rates" below), `bundleItems` (optional — makes this product a bundle), `sku` (optional, even without variants — variants carry their own; snapshotted onto each order item at checkout and shown as "Art.-Nr." on the invoice PDF, the order-confirmation email, and `/konto/bestellungen/[orderNumber]`) |
| `discount-codes` | Cart discount input (`/cart`, display-only on `/checkout`) | `code`, `type` (`percent`/`fixed`), `value`, `validFrom`/`validUntil`, `minOrderValue`, `maxRedemptions`, `redemptionCount` (server-incremented only), `active`. **Not public-read** — see Discount codes section below |
| `posts` | `/blog`, `/blog/[slug]` | `title`, `slug`, `categories` (`hasMany` relation to `categories` — a post can have several, joined with `", "` wherever rendered), `excerpt`, `thumbnail`, `content` (richText, supports custom Lexical blocks — Bild/Bildergalerie/Video/Zitat — rendered via `app/components/RichText.tsx`'s `@payloadcms/richtext-lexical/react` renderer with custom `JSXConverters`), `readTime` (auto-calculated on save from word count), `featured` (shown as the `/blog` hero post; most-recently-published wins if several are marked), `publishedAt`, `quoteLabel` (label + icon + underline shown next to every blockquote in `content`, default `"Merke dir:"` — leave empty to hide that framing, the blockquote text itself still renders), `relatedProduct` (optional relation to `products`, powers the "Passend dazu" card at the end of the post — leave empty to hide that card, or empty if the linked product has no `detailHref`), `seoTitle`/`seoDescription`/`seoImage` (each falls back to `title`/`excerpt`/`thumbnail` when empty, consumed by `/blog/[slug]`'s `generateMetadata()`) |
| `categories` | Blog post categorization | `name`, `slug` (unique per tenant, not globally) |
| `legal-pages` | `/impressum`, `/datenschutz`, `/agb`, `/widerruf` | `type` (`impressum`/`datenschutz`/`agb`/`widerruf`, one doc per type per tenant), `title`, `content` (richText), `attachment` (optional file, e.g. the Muster-Widerrufsformular PDF). Each page's "Stand: …" line is derived from this doc's own `updatedAt` (`formatMonthYear()` in `app/lib/format.ts`), not a hand-typed string — it updates automatically the moment an admin edits the content, no separate field to remember |
| `trust-badges` | Horizontal "Schneller Versand / Versandkostenfrei / Mit Liebe verpackt" row — shown on `/shop`, `/cart`, `/checkout`, `/widerruf`, `/agb`, 404 | `title`, `description` (supports `{{lieferzeit}}`/`{{kostenfreiab}}` placeholders, resolved by the frontend from `shipping-settings`/`shipping-methods` at render time — not by Payload itself), `icon`, `sortOrder` |
| `cart-trust-badges` | Sidebar bullets on `/cart` (title only) and `/checkout` (title + description) — deliberately a separate collection from `trust-badges` so the two pages can't drift into showing different claims | `title`, `description`, `icon`, `sortOrder` |
| `shipping-methods` | `/checkout` shipping selection | `title` (no day-range in the title text — that lives in `shipping-settings` now, keeping both in one title used to drift), `description`, `price`, `freeShippingThreshold` (per-method, optional — leave empty for a method that should never be free, e.g. Express), `active` (inactive methods are hidden, not shown disabled), `sortOrder` |
| `shipping-settings` | Delivery-time disclosure shown on `/shop`, homepage spotlight, ToDo-Karten, `/cart`, `/checkout`, `/versand` (Art. 246a §1 Abs.1 Nr.8 EGBGB requires this visible before checkout) | `handlingDaysMin`/`handlingDaysMax` (processing time before it ships), `transitDaysMin`/`transitDaysMax` (carrier time) — the app derives the combined total itself. One row per tenant. |
| `payment-methods` | `/checkout` payment selection | `title`, `icons` (array — e.g. 3 logos for "Kreditkarte"), `active`, `sortOrder` |
| `werkzeuge-cards` | Homepage "Meine Werkzeuge" 3-card grid | `title`, `description`, `icon`, `ctaLabel`, `ctaHref`, `sortOrder` |
| `testimonials` | Customer testimonial grids on `/todo-cards`, `/newsletter`, `/challenge` | `quote`, `name`, `role`, `avatar`, `page` (`todo-cards`/`newsletter`/`challenge` — which page's grid this appears in), `sortOrder`. The single-quote "photo band" testimonials on `/not-found` and `/bestellbestaetigung` are a different shape (no avatar/role) and stay hardcoded, not part of this collection. |
| `media` | Shared upload collection backing every `image`/`icon`/`thumbnail`/`attachment` field above | `alt` (required for images), `title` (optional display name for download links) |
| `orders` | Persisted checkout orders, `/konto/bestellungen*` | `orderNumber`, `invoiceNumber`/`invoiceIssuedAt`, `correctionInvoiceNumber`/`correctionInvoiceIssuedAt` (see "Invoice PDFs" below), `status` (`received`/`processing`/`shipped`/`delivered`/`cancelled`/`return_requested`/`returned` — the first 4 maintained by hand in the admin, no carrier API; the rest see "Order cancellation & returns"), `returnReason` (captured from the customer on a return request), full address/items (each with a snapshotted `taxRatePercent`/`bundleContents`)/totals at order time. **Not public-read** — created only via `ORDER_SERVICE_SECRET`, read/updated by admin or the order's own customer |
| `customers` | Storefront accounts — register/login/order-history, a second `auth: true` collection separate from the Payload admin's own `users` login | `customerNumber`, `firstName`/`lastName`/`email`, one default address, `cart` (server-side mirror), `emailVerified` (non-blocking). **Not public-read** — see "Orders & customer accounts" below |
| `number-ranges` | Admin-configurable prefix + running counter for customer/order/invoice/correction-invoice numbers — one row per tenant | `customerPrefix`/`customerNext`/`customerPadding`, `orderPrefix`/`orderNext`/`orderPadding`, `invoicePrefix`/`invoiceNext`/`invoicePadding`, `correctionInvoicePrefix`/`correctionInvoiceNext`/`correctionInvoicePadding` (Stornorechnung/Gutschrift — its own gapless sequence, not the same counter as `invoice*`, see "Invoice PDFs" below). **Admin-only**, no frontend read at all — internal to the two `beforeChange` hooks that assign these numbers |
| `email-templates` | Editable subject/heading/body/footer for all 10 transactional emails this shop sends (see "Email templates & Live Preview" and "Status-change emails" below) | `type` (`order-confirmation`/`password-reset`/`payment-method-switched`/`order-shipped`/`order-cancelled`/`order-return-requested`/`order-returned`/`order-tracking-added`/`order-tracking-corrected`/`order-delivered`), `subject`, `heading`, `bodyText`, `footerText`. Public-read, has a Live Preview button |
| `company-settings` | Structured business data for invoice PDFs *and* every email's legal footer (Anbieterkennzeichnung, see "Invoice PDFs" below) — one row per tenant, own **Company** admin group (not Commerce — this is business identity, not a storefront concern) | `sellerName`/`sellerStreet`/`sellerZip`/`sellerCity`/`sellerCountry`/`sellerEmail`, `vatId`, `taxRatePercent` (admin-editable, not hardcoded), `bankName`/`iban`/`bic` (`iban`/`bic` format-validated + uppercase-normalized; `bankName` stays free text — replaced a single free-text `bankDetails` field). **Not public-read** — admin or `ORDER_SERVICE_SECRET`. Has a Live Preview button — see "Company Settings & Live Preview" below |

All of the above except `company-settings`, `media`, `users`, `tenants`
are grouped in the Payload admin sidebar under **Commerce** (`products`,
`discount-codes`, `orders`, `customers`, `number-ranges`,
`email-templates`, `shipping-methods`, `shipping-settings`,
`payment-methods`, `trust-badges`, `cart-trust-badges`) or **Content**
(`posts`, `categories`, `legal-pages`, `werkzeuge-cards`, `testimonials`).
`company-settings` sits in its own **Company** group; `media`/`users`/`tenants`
sit under **Platform** — `users` and `tenants` are hidden from
non-super-admins' nav entirely, and every tenant-scoped collection's own
"assigned tenant" field is hidden from non-super-admins in the edit view
(though not yet the list view's column — see the infra README's Payload
CMS section for why that one's a harder fix).

**What an admin can actually configure without a code deploy, at a
glance:** product/shipping/payment catalog data and `active` toggles
(incl. per-product tax-rate overrides and defining a product as a bundle),
discount codes, all page content (blog/legal/testimonials/trust badges),
delivery-time disclosure (`shipping-settings`), order/customer/invoice
numbering schemes (`number-ranges`), all 10 email wordings
(`email-templates`, with Live Preview), and invoice seller data,
bank details, and VAT rate (`company-settings` — also what every email's
legal footer is sourced from). What still requires a code change:
adding a new *field* to any collection (needs a migration), payment
processing itself (not built), and anything structural in
`orders`/`customers` beyond `status`/`returnReason` and the profile fields
already exposed on `/konto/profil`.

Adding a *new field* to any collection above requires editing the
collection file in `docker/payload/src/collections/` and a migration,
which does need a deploy of the Payload service.

### Live Preview

`posts`, `legal-pages`, and `testimonials` support Payload's Live Preview —
opening a document in the Payload admin shows this app's real rendered page
in an iframe, updating as you type, no save required. `email-templates`
also has Live Preview, but against a synthetic page + sample data rather
than one of these three's own real page — different enough to cover
separately, see "Email templates & Live Preview" further below.

- **`app/api/preview/route.ts`** — validates `PAYLOAD_PREVIEW_SECRET`
  (matching value required on the Payload side too, or this route 401s) and
  a `path`, enables Next.js Draft Mode, then redirects into the real page.
  This is the link Payload's `livePreview.url` resolvers point at (see
  `docker/payload/src/lib/previewUrl.ts` in the infra repo) — never the page
  directly.
- Each supported page checks `draftMode().isEnabled` and renders a
  `"use client"` Live-Preview-aware component instead of the plain static
  one only when it's `true` — ordinary visitors are never in Draft Mode, so
  they always get the plain version with zero extra client JS:
  - `app/components/LiveRichText.tsx` — the 4 legal pages' body content
    (their headings/sidebars are hardcoded per page, not CMS-sourced, so
    `content` is the only field worth live-previewing there)
  - `app/blog/[slug]/components/LivePostContent.tsx` — title/excerpt/
    thumbnail/body of a blog post (the author bio card, "Weiterlesen" card,
    and Footer stay static — they either aren't post-specific or are about
    a *different* post, not the one open in the admin)
  - `app/components/LiveTestimonialsGrid.tsx` — the one testimonial
    currently open in the admin, merged by `id` into the rest of that
    page's already-fetched grid (Live Preview is inherently single-document,
    but this page renders several at once)
- All three use `@payloadcms/live-preview-react`'s `useLivePreview` hook and
  reuse the same mapping functions (`mapPayloadPost`, `mapPayloadTestimonial`,
  exported from `app/lib/payload.ts`) the plain server-side fetchers use, so
  the two code paths can't silently drift apart.
- `app/lib/payload.ts` deliberately never imports `next/headers` itself —
  callers (the Server Component pages) call `draftMode()` themselves and
  pass the result in as a plain `{ draft: boolean }` option. Importing
  `next/headers` anywhere in that module breaks the production build the
  moment a `"use client"` component (which also needs this file's mapping
  functions/types) tries to bundle it — a real RSC-boundary regression hit
  once already when adding this feature.

## Discount codes

Applied in `/cart` only (`/checkout` displays the already-applied result,
no second input) — real server-side validation, not just a client-side
check against Payload's public API, unlike most content on this site.

- **Manual input field on `/cart`** (`CartContent.tsx`) — a text field +
  "Anwenden" button, shown whenever no code is currently applied *and*
  Payload actually has at least one active code right now
  (`hasActiveDiscountCode()` in `discountServer.ts`, `where[active][equals]=true`,
  ISR-cached 60s — no point offering an open field that could never
  validate against anything). Once applied, the field is replaced by a
  read-only result + "Entfernen" link, shown regardless of that check (an
  already-applied code, e.g. from an older session, still needs somewhere
  to display even if no *other* code happens to be active right now).
  `?code=SAVE10` on the `/cart` URL still auto-applies once on arrival (a
  `useEffect` reading `useSearchParams()` — requires `/cart`'s `page.tsx`
  to wrap `CartContent` in `<Suspense>`, a Next.js requirement for any
  `useSearchParams()` consumer) regardless of `hasActiveDiscountCode()`
  too, so a marketing link still works without the shopper typing
  anything; if that auto-apply fails, the error shows even without the
  manual field present.
- **`app/lib/discountServer.ts`** (server-only, imported exclusively by the
  two route handlers below — never by a `"use client"` component, same
  reasoning as Live Preview's `next/headers` lesson above) talks to
  Payload's `discount-codes` collection using an `x-discount-service-secret`
  header (`DISCOUNT_SERVICE_SECRET`), since that collection isn't
  public-read.
- **`app/api/discount/validate/route.ts`** — read-only check (active /
  validity window / minimum order value / remaining redemptions), called
  when a shopper clicks "Anwenden" in the cart.
- **`app/api/discount/redeem/route.ts`** — re-validates, then increments
  the collection's `redemptionCount`. Called exactly once, from
  `CheckoutContent.tsx`'s `handlePurchase()`, right before the
  `OrderSnapshot` is written — a code that expired or hit its redemption
  cap between being applied in the cart and the actual purchase click
  fails the purchase with an inline error instead of silently completing.
- **`app/lib/discount.ts`** mirrors `lib/cart.ts`'s exact `localStorage` +
  `useSyncExternalStore` pattern, so the applied code survives the
  `/cart` → `/checkout` navigation the same way the cart itself does.
- **`app/lib/cartTotals.ts`** — `computeSubtotal()`/`computeCartTotals()`,
  factored out of what used to be independently-duplicated subtotal/
  savings/total math in `CartContent.tsx`, `CheckoutContent.tsx`, and
  `BestellbestaetigungContent.tsx`; now also folds in the discount amount
  (clamped so a total can never go negative). `OrderSnapshot` persists the
  applied `discountCode`/`discountAmount` so the confirmation page shows
  what actually happened, not a fresh re-derivation.
- Known, accepted limitation: the redeem route's read-then-increment isn't
  atomic against a true concurrent race on a capped code's very last
  redemption — not worth custom atomic SQL at this shop's traffic level.

## Cart & checkout

- **Cart** (`app/lib/cart.ts`) is entirely client-side, stored in
  `localStorage` under `ep_cart`, keyed by each product's `slug`. Still the
  source of truth while browsing — the server-side mirror (see below) only
  exists to carry a logged-in customer's cart across devices/browsers.
- **Add-to-cart is capped at actual remaining stock.**
  `Product`/its variants carry a real `maxQty` (`app/lib/payload.ts`'s
  `mapPayloadProduct()` — `null` when unlimited, i.e. backorder allowed or
  inventory untracked; a deliberate, narrow exception to that function's
  own "the public API has no reason to leak exact stock counts" comment,
  since the add-to-cart controls genuinely need it). `AddToCartButton`/
  `AddToCartInlineButton` disable (and show "Maximale Menge im Warenkorb")
  once the cart already holds that many; `/cart`'s quantity `<select>`
  caps its option range the same way instead of always offering a flat 1–9.
  `api/checkout/route.ts`'s own stock re-check stays as the authoritative
  server-side guard regardless.
- **`app/cart/components/RelatedProducts.tsx`** only ever suggests products
  not already in the cart — it stopped falling back to re-suggesting an
  already-in-cart product just to pad the grid out to 3 cards, so with a
  small catalog it can render fewer cards (down to 1, centered in the
  12-column grid) rather than recommending something already added.
- **`/checkout`'s "Jetzt kaufen" always goes through
  `POST /api/checkout`.** That route re-prices the entire cart server-side
  from Payload's live product data (never trusts client-submitted prices),
  re-validates+redeems a discount code exactly once, registers a new
  account inline if nobody's logged in yet ("Konto Pflicht" — see below),
  and only then creates the order in Payload's `orders` collection via
  `app/lib/orderServer.ts`. `subtotal`/`discountAmount`/`total` are each
  rounded to 2 decimals (`roundMoney()`) right before being persisted —
  plain float arithmetic on a summed/percent-discounted cart drifts into
  values like `84.30000000000001`, invisible wherever a display already
  ran the number through `formatPrice()`'s `toFixed(2)`, but stored as-is
  otherwise and visible raw in the Payload admin's plain number field for
  `total`. `app/lib/order.ts`'s `OrderSnapshot` is still
  written to `sessionStorage` for `/bestellbestaetigung` to read once, but
  its `orderNumber`/`orderDateIso` now come back from that Payload create
  call, not generated client-side.
- **Order confirmation email** is sent from `/api/checkout/route.ts`
  right after a successful `createOrder()` for Überweisung orders only —
  fire-and-forget
  (`app/lib/orderEmail.ts`'s `sendOrderConfirmationEmail()`), never blocks
  or fails the checkout response itself; a send failure alerts admin
  instead (`sendCriticalAlert`, lower severity than the "order not
  persisted" alert, since the order itself is safe either way). Content
  comes from the **published** `order-confirmation` row in Payload's
  `email-templates` collection — see "Email templates & Live Preview"
  below for how that's edited/previewed. As of the invoice PDF feature
  (see below), this same send also carries the order's invoice PDF as an
  attachment. Kreditkarte/PayPal orders defer this until payment is
  confirmed — see "Payment processing (Stripe)" below.

### Payment processing (Stripe)

Real payment capture for Kreditkarte/PayPal, via Stripe's Payment Element
(one integration covers both — see the approved plan this was built from,
`spicy-leaping-pizza.md`, for the full design rationale). Überweisung stays
exactly as before: no gateway involved, order goes straight to `received`.

- **`payment-methods`'s `provider` field** (Payload, admin-only) drives the
  branch — `'manual'` (Überweisung) or `'stripe'` (Kreditkarte/PayPal).
  `app/lib/payload.ts`'s `getPaymentMethods()` exposes it; the checkout
  route re-resolves it server-side, never trusts a client-submitted value.
- **Checkout UI collapses Kreditkarte + PayPal into one "Online-Zahlung"
  option** (`groupPaymentMethodsForCheckout()` in `app/lib/payload.ts`,
  used by `CheckoutContent.tsx`). Both admin rows still exist and both
  still need `provider: 'stripe'` — this is a display-layer grouping, not
  a data change. Reasoning: the PaymentIntent is created with
  `automatic_payment_methods: { enabled: true }` (Stripe's own recommended
  Payment Element pattern — Stripe itself decides which eligible method to
  show), so pre-selecting "Kreditkarte" vs. "PayPal" before that never
  actually restricted anything; it was redundant friction, not a real
  choice. The combined option shows a hint text ("die genaue Zahlungsart
  wählst du im nächsten Schritt") so the consolidation reads as intentional,
  not a missing option. Überweisung stays a separate, real option.
- **`paymentMethodTitle` is snapshotted as a neutral `"Online-Zahlung"`**
  at order-creation time for the `stripe` branch (the customer hasn't
  picked an instrument yet at that point) and **refined to the real one**
  (`"Kreditkarte"`/`"PayPal"`) once Stripe reports it —
  `resolveStripePaymentMethodLabel()` in `stripeProvider.ts` reads the
  confirmed PaymentIntent's `payment_method.type` in the webhook route and
  passes it to `confirm-payment` as an optional field. Best-effort: an
  unresolved label just leaves the neutral title in place. The
  `/checkout/verarbeitung` polling page also patches this into the
  provisional `sessionStorage` snapshot before promoting it, so
  `/bestellbestaetigung` shows the real instrument too, not the neutral
  placeholder.
- **`app/api/checkout/route.ts`, `provider === 'stripe'` branch**: creates
  a Stripe PaymentIntent *before* the order (`app/lib/payments/
  stripeProvider.ts`) — its id is known immediately and gets persisted as
  the order's own `providerReference` field at creation time, so the
  backend's abandonment-cleanup job can reconcile with Stripe later even
  if nothing else about this flow ever completes. The order is created
  with `status: 'pending_payment'`, `paymentStatus: 'pending'` — no
  invoice number yet, no confirmation email yet (both deferred to the
  webhook-driven confirm-payment step, on the backend). Right after, a
  best-effort (awaited, non-fatal) call attaches `{orderId, orderNumber}`
  as PaymentIntent metadata (`attachOrderMetadata`) — this is what lets
  the webhook resolve an incoming Stripe event back to a specific Payload
  order.
- **`app/checkout/components/PaymentStep.tsx`** renders in place of the
  address form once `/api/checkout` returns `requiresPayment: true` —
  Stripe's `PaymentElement` (real mode) or a "Testzahlung erfolgreich /
  fehlgeschlagen" button pair (test mode, see below). A card confirms
  in-place; PayPal (and 3-D-Secure challenges) redirect out and back via
  `return_url=/checkout/verarbeitung?orderNumber=...`.
- **`app/api/webhooks/stripe/route.ts`** — the real inbound webhook.
  Verifies `stripe-signature` against `STRIPE_WEBHOOK_SECRET`, reads the
  **raw** body (never `.json()` — the signature is computed over the exact
  bytes), handles `payment_intent.succeeded`/`.payment_failed`, and calls
  the backend's `POST /api/orders/:id/confirm-payment` (guarded by
  `PAYMENT_WEBHOOK_SECRET`, a secret distinct from `ORDER_SERVICE_SECRET`
  on purpose — least privilege, it can only hit this one action) with
  `{paymentStatus, providerReference, paidAt}`. Returns a non-2xx status on
  any internal failure so Stripe's own retry schedule (~3 days) provides
  resilience for free, rather than this app building its own retry queue.
  That backend endpoint flips the order to `received`, assigns the
  (until-then-deferred) invoice number, and queues the internal admin
  new-order notification — see the backend repo's own README for that
  half. It has no SMTP sender of its own, though: it returns a full order
  snapshot in its response instead, and **this webhook route is what
  actually sends the confirmation email + invoice PDF**
  (`app/lib/payments/confirmPaymentEmail.ts`, only when the response isn't
  `alreadyProcessed: true` — a repeat webhook delivery must never resend
  it), mirroring exactly what the checkout route already does inline for
  a manual/Überweisung order. Product photos in that snapshot's
  `items[].imageUrl` need no frontend change to work —
  `ConfirmPaymentOrderSnapshot`/`OrderConfirmationItem` already typed the
  field; the backend just wasn't populating it (fixed there, see its own
  README — needed `depth: 2` so `item.product.image` resolves to a real
  `Media` doc).
- **`/checkout/verarbeitung`** (`VerarbeitungContent.tsx`) is the
  `return_url` target. Neither a client-side `confirmPayment()` success nor
  landing back from a PayPal redirect is trusted as proof of payment on its
  own (a closed tab mid-redirect looks identical to success from here) —
  this page polls `/api/checkout/status?orderNumber=...` (session-scoped,
  so a guessed order number can't be used to probe someone else's payment
  status) until `paymentStatus` flips to `paid`, then promotes the
  provisional `sessionStorage` snapshot (`PENDING_ORDER_KEY`, written right
  before handing off to Stripe) to the real one (`ORDER_KEY`), clears the
  cart, and redirects to `/bestellbestaetigung` — exactly the same
  sessionStorage mechanism Überweisung orders already used, just populated
  a step later. On `failed`/`cancelled` it shows a retry message with the
  cart left intact (never cleared until payment actually succeeds); on a
  slow-to-arrive webhook it times out after ~15s with a "we'll email you"
  message rather than polling forever.

**Local testing without a real Stripe account** — `PAYMENT_TEST_MODE`
(defaults on whenever `STRIPE_SECRET_KEY` is unset, so a fresh `npm run dev`
never accidentally calls the real Stripe API): `app/lib/payments/index.ts`
swaps in `mockProvider.ts` instead of `stripeProvider.ts` — same interface,
so the checkout route and everything downstream of it runs unmodified.
`PaymentStep.tsx` shows "Testzahlung erfolgreich"/"Testzahlung
fehlgeschlagen" buttons instead of the real Payment Element; clicking one
calls `app/api/webhooks/stripe/test-confirm/route.ts`, which skips
signature verification (there's no real Stripe event to verify) and calls
the exact same backend `confirm-payment` endpoint the real webhook does —
so clicking "erfolgreich" exercises the *entire* real pipeline (deferred
invoice numbering, gated email, idempotency) end to end, it's only the
Stripe API call itself that's faked. That test-confirm route hard-404s
whenever `PAYMENT_TEST_MODE` isn't explicitly true, so it can never become
a reachable "mark any order paid" endpoint in production.

**Stripe is live in production for Kreditkarte.** `payment-methods` rows:
Kreditkarte → `provider: 'stripe'`, active; PayPal → `provider: 'stripe'`,
prepared but not yet activated on the Stripe account itself;
"Überweisung (Vorkasse)" → `provider: 'manual'`; "Sofortüberweisung"
prepared as `provider: 'stripe'` but `active: false` pending a logo (see
the backend's own README). `STRIPE_SECRET_KEY`, `STRIPE_WEBHOOK_SECRET`,
`NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY`, and `PAYMENT_WEBHOOK_SECRET` are set
in both Coolify and the backend's `docker/.env` (the backend's own copy of
`STRIPE_SECRET_KEY` is used only for `stripeRefund.ts`, Storno/Gutschrift
refunds). Going from test-mode keys (`sk_test_...`) to live-mode keys
(`sk_live_...`) is a straight swap of the same three Coolify variables
plus a new live-mode webhook endpoint (new `whsec_...`) — no code change.

### VAT display

Every price shown storefront-wide says "inkl. X% MwSt." with the *actual*
resolved rate (`app/lib/cartTotals.ts`'s `effectiveTaxRate(product,
defaultRate)` — a product's own `taxRatePercent` override if set,
otherwise the tenant default from `company-settings`), not a generic
"inkl. MwSt." disclosure — `getDefaultTaxRatePercent()` in
`app/lib/payload.ts` is a separate, ISR-cached (60s) fetch of just that one
number, deliberately not `getCompanySettings()` itself (that one is
`cache: "no-store"` for its invoice-generation callers, where always-fresh
bank details matter; the display rate only needs the same freshness every
other public catalog fetch already has).

A cart/checkout/order-confirmation *total* additionally shows the actual
€ amount of VAT included, not just a percentage — `computeTaxBreakdown()`,
imported from `@einfach-produktiv/invoicing` (a shared package consumed
by both this repo and the Payload backend as a git dependency — see
"Invoice PDFs" below; it used to be an independently-duplicated
`groupByTaxRate()` inside `invoicePdf.tsx`/`correctionInvoicePdf.tsx`,
both of which have since moved into that package too)
groups line items by their effective rate and reports each group's actual
tax amount; `app/components/VatBreakdown.tsx` renders a single "enthält
X% MwSt.: Y €" line when the cart/order has one rate, or one line per rate
when it spans more than one. Used on `/cart`, `/checkout`, `/bestellbestaetigung`,
the order-confirmation email (`emailTemplates.ts`'s `renderOrderConfirmationHtml`,
which already carried per-item `taxRatePercent` but didn't render it
before), and both account order pages (see "Orders & customer accounts"
below) — the account order list additionally shows up to 4 product
thumbnails per order row (`getProductImagesByIds()` in `app/lib/payload.ts`,
a plain product-id → image-url lookup separate from the slug-keyed
catalog, since an order only ever snapshots a numeric product id).

**None of this renders at all for a Kleinunternehmer tenant** — see
"Kleinunternehmerregelung" below for the full list of touched spots and
why some read a live setting and others a persisted per-order snapshot.

**Vorkasse instruction in the confirmation email.** The invoice PDF
already shows this (see `@einfach-produktiv/invoicing`'s own
`unpaidNoticeText`), but a customer often only glances at the email body
itself, not the attached PDF. `OrderConfirmationData`'s required
`isManualPayment: boolean` field is **explicitly set by each caller**
(checkout route's manual branch: `true`; the Stripe webhook path:
always `false`, since only a *paid* Stripe order ever reaches that send at
all), deliberately **not** derived from `paymentMethodTitle` inside
`emailTemplates.ts` itself — that string ("Online-Zahlung", "Kreditkarte",
"Überweisung (Vorkasse)", ...) is exactly the kind of thing a
payment-methods rename could silently break (see `isPaidImmediately()` in
the invoicing package). When `isManualPayment` is true, `vorkasseNotice()`
renders a full-width block (own row, `margin-top: 20px` — not squeezed
into the Gesamtsumme table) naming the bank details
(`CompanySettings.bankName`/`iban`/`bic`) and the "processed within 1–2
business days after payment received" note.

### Checkout state persistence

`app/lib/checkoutDraft.ts` — `localStorage` under `ep_checkout_draft`,
plain read/write functions (not `useSyncExternalStore` like `cart.ts`/
`discount.ts`: `CheckoutContent` is this draft's only reader, no
cross-component subscription to keep in sync). Every address-card field
(name, email, delivery method, street/Packstation, PLZ/Ort/Land, the
shipping-address-override fields below, newsletter opt-in) plus the
selected shipping/payment method is now a controlled input backed by this
draft, restored on mount (a `useEffect`-deferred read, same SSR/hydration-
mismatch avoidance as `BestellbestaetigungContent`'s own sessionStorage
read) and cleared on a completed purchase. `password` is deliberately
excluded — stays a plain uncontrolled, unpersisted input.

### Optional deviating shipping address

"1. Rechnungsadresse" always collects a plain street address now — no
Lieferart (Lieferadresse/Packstation) toggle there anymore, since a
Packstation isn't a valid billing address for an invoice. A separate
checkbox ("Abweichende Lieferadresse verwenden") reveals a second address
section with its *own* delivery-method toggle (own name + delivery method +
street/Packstation/PLZ/Ort/Land, plus optional Firma and
Kontakt-E-Mail/Telefon handed to the shipping carrier only, never used for
customer communication — that stays the account email) — that's the only
place Packstation delivery is offered at all. When used, the order's
original address fields stay the **billing** address (used for the
invoice's "An" block regardless), and the `shipping*`-prefixed fields
(`hasDifferentShippingAddress`,
`shippingFirstName`/`shippingLastName`/`shippingDeliveryMethod`/
`shippingStreet`/`shippingPackstationNumber`/`shippingPostNumber`/
`shippingZip`/`shippingCity`/`shippingCountry`/`shippingCompany`/
`shippingContactEmail`/`shippingContactPhone` — mirrored 1:1 on the
Payload `orders` collection, see the Payload README; there's no
`shippingVatId` — VAT ID is a billing-only concept, deliberately not
mirrored) determine where the order actually ships. `/api/checkout/route.ts`
validates the override the same way it already validated the primary
address (required fields, street-xor-Packstation depending on the chosen
delivery method). The invoice PDF shows a third "Lieferadresse" address
block alongside Von/An when set (see "Invoice PDFs" below);
`/konto/bestellungen/[orderNumber]` shows both addresses too, relabeling
the first one "Rechnungsadresse" instead of "Lieferadresse" only once
there's an actual second address to distinguish it from. `/konto/profil`
can store this same deviating-shipping-address shape (same checkbox
pattern, same fields) as a saved default, prefilling checkout's own
section for a returning customer instead of always starting blank.

### DHL checkout integrations

Three checkout-facing pieces, each backed by the Payload backend's
tenant-configurable `dhl-settings` and gracefully absent (the underlying
calls 404) whenever a tenant hasn't activated the matching DHL
sub-integration — see `docker/payload`'s `src/lib/shipping/README.md` for
the backend side.

- **`app/lib/shippingDhl.ts`** — a thin client for the backend's two
  public DHL endpoints (Postnummer validation, DataFactory address
  autocomplete); its own small copy, not part of the shared invoicing
  package.
- **`app/api/checkout/validate-dhl-postnumber/route.ts`** and
  **`app/api/checkout/autocomplete-address/route.ts`** — Next.js API
  routes proxying to the backend, since `CheckoutContent.tsx` is a Client
  Component and DHL credentials are tenant-specific (live in Payload) —
  the browser never talks to Payload's DHL endpoints directly.
- **`app/checkout/components/AddressAutocomplete.tsx`** wraps the billing
  and shipping street inputs with a debounced DHL DataFactory suggestion
  dropdown; selecting a suggestion also fills zip/city.
- **Postnummer live validation** — `CheckoutContent.tsx`'s
  `handlePostNumberBlur` (same shape/status-state pattern as the VAT-ID
  blur check) checks the Packstation Postnummer against DHL on blur, once
  the existing format check (6–10 digits) already passes.
- **Return-label download** — `/konto/bestellungen/[orderNumber]` shows a
  "Retourenschein herunterladen" link once the backend has generated a DHL
  return label for that order (`order.dhlReturnLabelMedia`, resolved via
  `getMediaUrlById()` in `app/lib/payload.ts`).

### Destination countries (Payload-configurable)

Both country `<select>`s (billing, and the shipping-address override)
are fed by `getShippingCountries()` (`app/lib/payload.ts`) reading
Payload's `shipping-countries` collection (`name`, `plzDigits`,
`active`, `sortOrder`) — not a hardcoded array anymore. `plzDigits` also
drives PLZ's own `maxLength`/pattern validation (`validateZip()` in
`CheckoutContent.tsx` builds a `country → digit count` map from this
list), so an admin adding a country in Payload doesn't need a frontend
deploy to make it selectable, and the PLZ format check automatically
matches whatever digit count that country's row specifies. Seeded with
Deutschland (5 digits) and Österreich (4) — matching what this checkout
already offered before this became configurable. Adding a country here
(e.g. Schweiz) makes it immediately selectable at checkout; it does
**not** by itself add any customs/export-invoice handling or affect VAT
exemption eligibility (see "VAT exemption" below — that's still a
separate, deliberately-not-Payload-configurable legal decision).

### Product variants

A cart line's identity is `(id, variant)` together, not `id` alone —
`app/lib/cart.ts`'s `CartItem` gained an optional `variant?: string` field
(the selected `products.variants[].name`), and every function that used to
match a line by `id` (`addToCart`/`removeFromCart`/`setQuantity`) now
matches by both via a shared `sameLine()` helper, so two lines for the
same product with different variants stay genuinely separate entries
instead of merging or clobbering each other. `variant` undefined on both
sides (the common no-variants case) still matches by simple equality —
every pre-existing call site that never passes a variant keeps working
unchanged.

**Where a variant gets picked**: both `AddToCartInlineButton`
(`/shop`, `/cart`'s related-products grid) and `AddToCartButton` (the
marketing-page-specific one on `/todo-cards`' Hero + Pricing panel and the
homepage spotlight) render a `<select>` above the button when their
`variants` prop is non-empty, defaulting to the first *in-stock* variant.
All five call sites already fetch the full product server-side
(`getProducts()`/`getProductBySlug()`/`getSpotlightProduct()`), so
`product.variants` and `product.outOfStock` are simply passed straight
through — no separate data-fetch needed for `AddToCartButton`'s two pages.

**Out-of-stock UI**: `app/lib/payload.ts`'s `isOutOfStock()` derives
`Product.outOfStock` (and each `variants[].outOfStock`) from
`trackInventory`/`stock`/`allowBackorder` — true only when inventory is
tracked, backorders aren't allowed, and `stock <= 0`. Both add-to-cart
buttons disable themselves and show "Ausverkauft" for whichever variant is
currently selected (or the plain product, when there are no variants);
`ProductGrid.tsx` additionally shows an "Ausverkauft" badge (replacing any
discount/low-stock badge — a sold-out product has nothing else useful to
show) once *every* variant of a product is out — one sold-out variant
among several just reads as such in the picker itself, not as a
misleading blanket badge.

**Low-stock warning**: `app/lib/payload.ts`'s `isLowStock()` derives
`Product.lowStock` (and each `variants[].lowStock`) from `trackInventory`/
`stock`/`lowStockThreshold` the same way `outOfStock` is derived — true
only when inventory is tracked, stock is above zero (out-of-stock has its
own distinct badge, the two never combine), and at/below the product's own
`lowStockThreshold`. Neither raw `stock` nor `lowStockThreshold` is
exposed in the public `Product` type, only this derived boolean — the
public API has no reason to leak exact counts. Shown as a "Nur noch wenige
verfügbar" **text line** (`text-warning`, the same `--color-warning` token
in `globals.css`, distinct from the brand-colored discount badge) next to
the price on `ProductGrid.tsx`/`ProductSpotlight.tsx`/`RelatedProducts.tsx`/
todo-cards' `TodoKartenHero.tsx` and `Pricing.tsx` (both — the page has two
independent purchase CTAs, hero and pricing panel, each with their own
price/delivery block) and — variant-specific, not
"any variant low" — under the product name in `CartContent.tsx`'s own
cart line items, plus the existing `"(nur noch wenige)"` variant-select
suffix in `AddToCartButton`/`AddToCartInlineButton`. The image-overlaid
top-left pill (`position: absolute`, outside layout flow) now shows only
Ausverkauft/discount — low-stock moved off the image into text on request,
since a shopper scanning product photos for "-20%" style badges reads a
long low-stock sentence pinned to the image as clutter, and a customer
already in the cart with that product had no low-stock signal there at
all before this. The earlier version of this text line (removed once,
see git history) broke equal-height card alignment in `ProductGrid.tsx`/
`RelatedProducts.tsx` by only rendering when `lowStock` was true, so
cards with/without the line ended up different heights; this version
always renders the line's slot (`min-h-[1.05rem]`, empty when not
low-stock) so every card in a row reserves the same space regardless of
state — `ProductGrid.tsx` additionally still has its `flex-1` spacer
pinning the add-to-cart button to the same Y as before, so the reserved
height is belt-and-suspenders there, but load-bearing in
`RelatedProducts.tsx`, which has no such spacer. Only "Ausverkauft" still
wins outright over the discount pill, since it replaces it.

**Pricing**: `app/lib/cartTotals.ts`'s `effectivePrice(entry, product)` —
a selected variant's `priceOverride` wins over the base `product.price`
(falling back to it when unset or no variant selected). Every cart/
checkout/order-confirmation total (`computeSubtotal`, `computeCartTotals`,
and each page's own per-line price display in `CartContent.tsx`,
`CheckoutContent.tsx`, `BestellbestaetigungContent.tsx`) goes through this
instead of reading `product.price` directly. The checkout route
(`/api/checkout/route.ts`) re-validates the requested variant server-side
too — same "never trust the client" reasoning as price re-derivation
generally: a `line.variant` naming something that doesn't exist on that
product (removed, or a tampered request) fails the whole checkout rather
than silently falling back to the base price. It also re-checks stock at
that same point — depth-in-defense, not just the disabled button UI above
— rejecting the order when the resolved product/variant has
`trackInventory` on, `allowBackorder` off, and less `stock` than the
requested quantity.

**Snapshotting**: `orders.items[].variantName` captures which variant was
picked at order time (same "snapshot, not a live relationship" reasoning
as `bundleContents`) — shown as a parenthetical next to the product name
on the order-confirmation email, both invoice PDF types, and the
order-detail page. The server-side cart mirror
(`Customers.cart[].variantName`, synced via `/api/account/cart`) carries
the same field so a variant selection survives a login/logout cycle, not
just the current session.

See the Payload README's "Inventory & product variants" section for the
backend data model (`products.variants`, stock bookkeeping) this all
builds on.

### Tracking numbers

`orders.carrier`/`trackingNumber` (admin-entered in Payload, no carrier
API) show as a clickable link on `/konto/bestellungen/[orderNumber]` when
set — `@einfach-produktiv/invoicing`'s `buildTrackingUrl(carrier, trackingNumber)`/
`CARRIER_LABELS` (imported from the package's main barrel) are shared with
the Payload backend, so the link an admin sees generated in the
`order-shipped` email matches exactly what a customer sees here. Falls
back to plain (non-linked) text for `carrier: 'other'`, which has no known
URL pattern.

### Product bundles & per-product tax rates

Both resolved server-side in `/api/checkout/route.ts`, at the same point
prices are already being re-derived from live Payload data (never trusted
from the client):

- **Tax rate**: `product.taxRatePercent ?? companySettings.taxRatePercent`
  — a product's own override if set, otherwise the tenant-wide default
  from `company-settings` (fetched alongside the product catalog,
  `Promise.all([fetchProductsBySlug(), getCompanySettings()])`). Snapshotted
  onto `orders.items[].taxRatePercent` at order creation — see the Payload
  README's "Per-product tax rates" section for why this has to be a
  snapshot, not a live lookup.
- **Bundles**: `describeBundleContents()` resolves a product's
  `bundleItems` (Payload relationship, populated via `fetchProductsBySlug()`'s
  `depth: 2` fetch — one level deeper than the `depth: 1` `image` alone
  needs, since `bundleItems.product` is a relationship nested inside an
  array field) into a plain string like `"2× ToDo-Karten, 1× Wochenplaner"`,
  snapshotted onto `orders.items[].bundleContents`. A bundle is otherwise
  just a regular product everywhere else in this app — same cart/checkout/
  pricing code path, no special-casing needed, since it's just a product
  with an extra field (see the Payload README's "Product bundles" section
  for why it's modeled that way instead of a separate collection).

## Invoice PDFs

Generated **synchronously at checkout** and attached to the order
confirmation email — not just an on-demand download — per an explicit
product decision that a customer should always have the invoice in their
inbox, not only in `/konto/bestellungen`.

- **`@einfach-produktiv/invoicing`** — a small standalone package
  (`git.mk360.de/Marco/einfach-produktiv-invoicing`, public repo, no
  secrets in it) holding every invoice/correction-invoice renderer plus
  `computeTaxBreakdown()` (see "VAT display" above) and shared
  formatters, consumed here **and** by the Payload backend as a git
  dependency (`"@einfach-produktiv/invoicing":
  "git+https://git.mk360.de/Marco/einfach-produktiv-invoicing.git#main"`
  in `package.json`). Ships raw TS/TSX source, no build step of its own —
  this app's `next.config.ts` lists it under `transpilePackages` so this
  app's own bundler compiles it, same as first-party code, the same
  pattern a monorepo tool like Turborepo uses for internal packages
  without actually needing a monorepo — see that package's own README
  for the full renderer/formatter surface.
- **`InvoiceDocument`** — a `@react-pdf/renderer` `Document`, not
  HTML-to-PDF or a headless browser (Puppeteer/Chromium would be a
  heavier footprint on a VPS already running several other containers).
  Built-in Helvetica rather than a registered web font — this renders
  inside a fire-and-forget checkout step, and a font-fetch failure there
  would be one more way to silently lose the attachment for no real
  design benefit; brand color/spacing still carries the visual identity
  via `StyleSheet`.
- **Layout**: a header separated by a bold brand-colored rule (not a
  filled color band — a plain line reads cleaner than a solid block of
  color across the top) with the wordmark + "RECHNUNG" label, seller/buyer
  addresses, invoice number/date/order-reference/USt-IdNr. shown as small
  bordered "meta boxes" rather than a plain text row, a rounded/bordered
  item table, and a shaded summary card for the totals — deliberately
  closer to the site's own card-based UI language than a generic invoice
  template. The footer is pinned to the bottom of the page
  (`position: absolute` + react-pdf's `fixed` prop), not just wherever the
  content flow happens to end. Item rows share one uniform tinted
  background, no alternating white/tinted zebra striping.
- **"Bereits beglichen" confirmation**: shown next to the summary card
  whenever `order.paymentMethodTitle` is anything other than
  `"Überweisung"` (bank transfer) — Kreditkarte and PayPal both settle at
  checkout, so the invoice says so explicitly (`isPaidImmediately()`, in
  the shared package's `invoicePdf.tsx` — "Überweisung" is the one method
  named explicitly as the exception, rather than hardcoding a list of
  "immediate" titles that would need updating every time a new payment
  method is added in Payload). Rendered as plain green text, not a tinted
  pill/badge box. This one is genuinely conditional on the order's own
  payment method — unlike the bank-details line below, which prints
  unconditionally.
- **Bank details**: `company-settings.bankName`/`.iban`/`.bic` — `iban`/
  `bic` structured and independently format-validated (uppercased/trimmed
  on save too, so "de123..." doesn't fail validation just for being
  lowercase — same normalization `discount-codes.code` already used),
  `bankName` stays free text since there's no fixed format to validate a
  bank's display name against — structured, discrete PaymentMeans data
  rather than a single free-text field, per EN16931. When `iban` or `bic`
  is set, the footer prints "Bankverbindung: [Bankname ·] IBAN … · BIC …"
  **always**, regardless of the order's payment method — a card/PayPal
  customer might still want the seller's bank details for other reasons
  (e.g. a refund).
- **Summary layout is a genuinely additive chain.** The summary card
  reads Zwischensumme → Rabatt (if any) → Versand → a divider → Gesamt,
  using the order's own raw `subtotal`/`discountAmount`/`shippingCost`/
  `total` fields directly — every row above the divider actually sums to
  the number below it. The per-rate tax breakdown (from
  `computeTaxBreakdown()`, which distributes discount/shipping
  proportionally across each tax-rate group before computing net/tax, per
  how ancillary costs are legally apportioned across rates) sits **below**
  Gesamt as an "enthält X% MwSt.: Y €" annotation (one line per distinct
  rate, informational — not part of the additive stack above it), the
  same "contained within, not an extra deduction" framing
  `VatBreakdown.tsx` uses on `/cart`/`/checkout` (see "VAT display"
  above). Applies to both the original invoice and its Storno/Gutschrift,
  which has its own equivalent chain (Zwischensumme → the discount
  reversal, "Rabatt (entfällt)", a positive add-back since the original
  discount no longer applies once everything's undone → Versand →
  Gesamt; a Gutschrift shows Gesamt alone, since it never reverses
  shipping/discount in the first place — see the Payload README's "How a
  Stornorechnung/Gutschrift relates to the original invoice"). When the
  order is VAT-exempt (see "VAT exemption" below), this annotation reads
  "Steuerfreie innergemeinschaftliche Lieferung (§4 Nr. 1b UStG)" instead.
- **Netto row**: a dedicated "Netto" row sits between Gesamt and the
  "enthält X% MwSt." annotation on every invoice this shop issues
  (original, Storno, Gutschrift alike) — businesses read this directly
  for their own input-tax deduction instead of computing Gesamt minus
  MwSt by hand. Shown unconditionally, including on VAT-exempt orders
  (net and Gesamt happen to be the same figure there).
- **Product thumbnails**: each item row shows a small product image —
  resolved from the order-confirmation data's already-available
  `imageUrl` for the checkout-time attachment, or via
  `getProductImagesByIds()` (see "VAT display" above) for the on-demand
  re-download route, since a stored order item only snapshots a numeric
  product id, not an image URL.
- **Bundle contents**: an item row for a bundle product also shows the
  small muted `bundleContents` sub-line snapshotted at order time (see
  the Payload README's "Product bundles" section).
- **Shipping address**: when `order.hasDifferentShippingAddress` is set
  (see "Optional deviating shipping address" above), a third
  "Lieferadresse" address block joins Von/An (three ~30%-width columns
  instead of two ~45%-width ones) — otherwise unchanged, two columns as
  before. `USt-IdNr.` no longer repeats in a header meta box — it already
  lives in the footer, printing it twice was redundant.
- **Buyer B2B fields**: when the order has a `companyName`/`vatId` (see
  "B2B checkout fields" below), the "An" block shows `companyName` as its
  own line above the contact person's name, and `vatId` as its own line
  below the address (labelled "USt-IdNr. …") — the buyer-side counterpart
  to the seller's own VAT ID already shown in the footer.
- **`app/lib/invoiceData.ts`** (still local to this repo — a thin
  server-only wrapper, not part of the shared package) — `generateInvoicePdf(order, seller)` /
  `generateCorrectionInvoicePdf(kind, order, seller)`, the render
  entrypoints every caller below goes through; both just call straight
  into `@einfach-produktiv/invoicing`'s `renderInvoicePdf()`/
  `renderCorrectionInvoicePdf()`. `seller` (`company-settings`
  data) is passed in rather than fetched inside these functions, so a
  caller that also needs it for something else in the same request (e.g.
  `orderEmail.ts`'s legal email footer, see "Legal footer (Anbieterkennzeichnung) on every email" below)
  fetches it once via `getSellerForInvoice()`, not twice.
- **Original invoice — called from two places, same render function:**
  `app/lib/orderEmail.ts` (checkout attachment — a PDF-generation failure
  here does **not** sink the confirmation email itself, it just sends
  without the attachment and alerts admin) and
  `app/api/account/orders/[orderNumber]/invoice/route.ts` (GET, customer's
  own order only, "Rechnung herunterladen" on
  `/konto/bestellungen/[orderNumber]`) — a re-download always matches what
  was originally emailed, since `invoiceNumber`/`invoiceIssuedAt` are
  assigned exactly once, server-side, at order creation (Payload's
  `orders.ts` `beforeChange` hook — see the Payload README) and never
  regenerated.
- **Correction invoice (Stornorechnung/Gutschrift) — same "no file
  storage" approach.** The *real* document is generated once, Payload-side,
  the moment an order reaches `cancelled`/`returned` (see the Payload
  README's "How a Stornorechnung/Gutschrift relates to the original
  invoice" section for the full legal/mechanical reasoning) and attached
  to that status email. This repo's own `/konto/bestellungen/[orderNumber]`
  "Stornorechnung/Gutschrift herunterladen" button
  (`app/api/account/orders/[orderNumber]/correction-invoice/route.ts`)
  calls the exact same `renderCorrectionInvoicePdf()` from
  `@einfach-produktiv/invoicing` the backend used to generate the
  original — not a ported approximation anymore (that used to be a
  separate, hand-duplicated copy; see the shared package's README) — so a
  re-download is now structurally guaranteed to match what was emailed,
  not just guaranteed by careful manual syncing. No PDF is ever persisted
  to disk/S3/Media: `correctionInvoiceNumber`/`correctionInvoiceIssuedAt`
  are immutable once set (Payload's `beforeChange` hook), so re-rendering
  from the order's own stored data always reproduces the identical
  document — the underlying data is already durable in Postgres, and
  deterministic regeneration needs no cleanup or storage cost, same
  reasoning already applied to the original invoice. Also has product
  thumbnails (same resolution approach as the original invoice) and, for a
  Stornorechnung specifically, an explicit "Versand" summary line — it was
  previously only folded silently into the tax-rate groups' scaled gross
  amounts, with no line stating how much of the reversed total was
  shipping. A Gutschrift never shows this line, since it never reverses
  shipping in the first place (see the reasoning below).
- **Numbering**: `invoiceNumber` and `correctionInvoiceNumber` each come
  from their own gapless counter on Payload's `number-ranges` collection
  (`invoicePrefix`/`Next`/`Padding` vs. `correctionInvoicePrefix`/`Next`/
  `Padding` — a Stornorechnung/Gutschrift has its own sequence, distinct
  from ordinary invoices). Both are assigned via a single atomic `UPDATE ...
  RETURNING` against Postgres (Payload's backend `numberRange.ts`), not a
  read-then-write across two separate calls — see the Payload README's
  "Number ranges" section for why that distinction actually matters for
  §14 UStG.
- **`company-settings`** (Payload collection, structured seller data —
  name/address/`vatId`/`taxRatePercent`/`bankName`/`iban`/`bic`) is fetched via
  `getCompanySettings()`/`getSellerForInvoice()`, authenticated the same
  way as order creation (`x-order-service-secret` header,
  `ORDER_SERVICE_SECRET`) since it's not public-read (holds bank details)
  but does need to be reachable from this app's own server-side code, not
  just from inside Payload's admin. **Currently seeded with placeholder
  data** ("Björn Wendt", "Musterstraße 12", USt-IdNr. "DE123456789", a
  placeholder IBAN/BIC) mirroring the Impressum's own placeholder content
  — real business details need to be entered in the Payload admin before
  an invoice generated from this is legally valid. `taxRatePercent` is
  deliberately a configurable admin field, not a hardcoded `19` in the
  renderer, per an explicit decision to keep the VAT rate editable without
  a code change.
- §14 UStG line items: seller/buyer address, invoice number + date, order
  reference, per-item quantity/price, net subtotal per rate, tax rate +
  amount per rate, gross total — all on the PDF, not just the summary the
  confirmation email's HTML already shows.
- **E-invoicing (ZUGFeRD/EN16931).** Every invoice generated above is
  actually a Factur-X-EN16931 hybrid PDF/A-3 (the same visual PDF, plus an embedded
  machine-readable `factur-x.xml`), for every order, not just B2B — see the
  shared package's own README for the full phased build (`@e-invoice-eu/core`,
  atomic invoice numbering, a self-hosted Mustang-CLI CI pipeline that
  validates every push to that package against real EN16931/PDF-A-3
  conformance rules).

### B2B checkout fields

Optional "Firma"/"USt-IdNr." fields sit right under Vorname/
Nachname in `/checkout`'s Card 1 — neither is required just because the
other is filled in (a sole proprietor might give a VAT ID with no separate
company name, and vice versa). Format-validated client- and server-side
(`@einfach-produktiv/invoicing`'s `isValidVatId()`/`normalizeVatId()`, same EU-format
regex as `company-settings.vatId` on the backend), persisted through
`checkoutDraft.ts` like every other Card 1 field, and saved as a
`Customers` profile default (`/konto/profil`) that prefills future
checkouts — `Orders` keeps its own independent snapshot regardless, same
"a later profile edit must never rewrite what an order actually said"
reasoning as every other snapshot field. Shown on the invoice PDF's "An"
block (see "Invoice PDFs" above) and threaded through both invoice
download routes and the correction-invoice email.

### VAT exemption (innergemeinschaftliche Lieferung)

A cross-border EU B2B sale — Österreich is the
eligible destination (`isExemptionEligibleCountry()` in
`app/lib/vatExemption.ts`, hardcoded, deliberately **not** read from the
Payload-configurable `shipping-countries` list above — eligibility is a
legal decision, not a shipping-logistics one, so an admin adding a new
destination country can't accidentally also grant it a VAT exemption) —
to a buyer whose VAT ID a live lookup against the EU's public VIES
service actually confirms is registered gets zero-rated per §4 Nr. 1b
UStG. Deliberately *not* based on format-validity alone: an unverified
VAT ID zero-rating an invoice is a real compliance risk (if it later
turns out unregistered, the seller retroactively owes the VAT itself).

- **`@einfach-produktiv/invoicing/vies`** (server-only entrypoint) —
  `checkVatIdViaVies()` calls the European Commission's public VIES REST
  API (`POST .../check-vat-number`) directly, server-side only.
- **`app/lib/vatExemption.ts`** — `destinationCountry()` picks the actual
  place the goods ship to (the shipping-address override's country when
  set, billing country otherwise — the exemption depends on where the
  goods physically move, not necessarily the invoice address);
  `computeExemptTotals()` de-grosses every item's price and the shipping
  cost from their normal VAT-inclusive catalog figures to net, since the
  whole point of the exemption is that the buyer pays less, not that this
  shop quietly keeps the VAT portion as extra margin.
- **VAT-ID *validity* and the exemption *decision* are two separate
  questions.** `app/api/checkout/validate-vat/route.ts`/`app/api/checkout/route.ts`
  check any format-valid VAT ID against VIES regardless of destination
  (data quality — worth knowing whether it's real at all, same reasoning
  as `company-settings.vatId`'s own check below) — the exemption itself
  still only applies when the destination is *also* Österreich. A
  validated German VAT ID never zero-rates a domestic sale, no matter how
  real it is.
- **Checkout UX**: the USt-IdNr. field's blur gives instant feedback for
  any country — "✓ USt-IdNr. bestätigt" (plus "— Lieferung wird steuerfrei
  berechnet." only when the destination actually qualifies) flips the
  sidebar total to the exempt (de-grossed) figures live, as a preview.
  `app/api/checkout/route.ts` re-runs the exact same VIES check server-side
  at submit time regardless, as the actual source of truth — the
  client-side result is never trusted. **VIES being unreachable fails
  closed on the exemption**: normal VAT applies, never a guessed exemption
  (contrast the Payload backend's own `company-settings.vatId` VIES check,
  which fails open, since that one only needs to catch an admin's
  data-entry typo, not decide a tax rate). On an unconfirmed VAT ID, the
  field re-focuses so the customer's attention returns there without
  also selecting the whole existing value — a stray keystroke while just
  glancing at the error shouldn't wipe out what was already typed. This
  same "re-focus the failing field" behavior applies generically to *any*
  checkout field that fails its own blur validation, not just this one —
  see the bullet below.
- **Every other checkout field is blur-validated too** — inline red
  error text appears the moment a field loses focus (required fields, email format, PLZ digit
  count per country, Packstation/Postnummer digit count), not only when
  the browser's native `pattern`/`required` validation kicks in at submit.
  The native attributes stay in place as a fallback for any field somehow
  never blurred (e.g. autofill). `setFieldError(name, message, refocusEl?)`
  (`CheckoutContent.tsx`) takes an optional element to refocus whenever the
  message is non-empty — every field's own `onBlur` passes `e.target`, so
  a field that fails validation gets focus put right back on it
  generically, not just the USt-IdNr. special case above.
- **Persistence**: `Orders.vatExempt`/`vatIdValidatedAt` (Payload backend)
  record the outcome, decided once server-side, never editable in the
  admin. `vatIdValidatedAt` is set for *any* VIES-confirmed VAT ID
  (data-quality audit trail), independently of whether `vatExempt` is also
  true — see the Payload README's "B2B checkout & VAT exemption" section
  for the full field/audit-trail reasoning and the invoice PDF/EN16931 XML
  side of this feature.
- **Every fixed-length numeric field also hard-caps input length** — PLZ
  (`maxLength` = the selected country's own digit count), USt-IdNr.
  (`14`), Packstationnummer (`3`)/Postnummer (`10`, on the backend), on
  top of their own `pattern`/`validate` format checks.
- **`/bestellbestaetigung`** mirrors the same exempt-totals branch from the
  persisted `OrderSnapshot.vatExempt` flag (it otherwise re-derives totals
  live from the current catalog, which would show the wrong, VAT-inclusive
  figures for an exempt order).

### Kleinunternehmerregelung (§19 UStG)

`company-settings.kleinunternehmer` — a standing per-tenant setting
(Payload backend), not a per-order decision like the VAT exemption above
— when on, this tenant never charges VAT on anything, domestic or
cross-border. See the Payload README's own "Kleinunternehmerregelung"
section for the field/collection side; this one covers the frontend.

- **`api/checkout/route.ts`** forces every item's `taxRatePercent` to `0`
  when `getCompanySettings().kleinunternehmer` is on — deliberately
  **without** de-grossing `unitPrice` the way `vatExempt` above does
  (that exemption zero-rates what would otherwise be a positive-rate
  charge, so de-grossing means the buyer pays less; a Kleinunternehmer
  never charged VAT on the sale to begin with, so the catalog gross price
  already *is* the actual net charge — confirmed with the user as the
  intended business decision, not an engineering default). The VIES
  lookup/`isExemptionEligibleCountry()` check is skipped entirely in this
  branch too — there's no VAT for the intra-community rule to exempt
  either. Snapshotted onto the new order as `Orders.kleinunternehmer`
  (mirrors `vatExempt`'s own snapshot reasoning — see the Payload README).
- **Storefront "inkl. X% MwSt." hints** — four spots read the *live*
  setting (`getKleinunternehmer()` in `app/lib/payload.ts`, same ISR-cached
  60s freshness as `getDefaultTaxRatePercent()`) and drop the MwSt. clause
  entirely when it's on, since there's no order yet at that point to
  snapshot from: `ProductGrid.tsx` (shop grid), `RelatedProducts.tsx`
  (cart's upsell row), `Pricing.tsx`/`TodoKartenHero.tsx` (ToDo-Karten
  landing page), `ProductSpotlight.tsx` (homepage). `Pricing.tsx`/
  `ProductSpotlight.tsx` keep "zzgl. Versand" on its own when the MwSt.
  clause drops; the other two had no such trailing clause to preserve.
- **Every already-placed-order display reads the persisted snapshot
  instead** — `OrderSnapshot.kleinunternehmer` (`app/lib/order.ts`,
  written into `sessionStorage` at checkout, read by
  `BestellbestaetigungContent.tsx`) and `CustomerOrderDetail.
  kleinunternehmer` (`app/lib/customerAuth.ts`, read by
  `/konto/bestellungen/[orderNumber]`) — never the live company-settings
  value, for the identical "don't retroactively rewrite an already-issued
  invoice's tax treatment" reason `vatExempt` already established. Both
  pages replace the per-item "inkl. X% MwSt." hint and the `VatBreakdown`
  summary with "Gemäß § 19 UStG wird keine Umsatzsteuer berechnet." —
  taking precedence over the `vatExempt` note wherever both would
  otherwise apply. `CheckoutContent.tsx`'s live VIES-exemption *preview*
  is also gated off (`!kleinunternehmer && ...`) so a Kleinunternehmer
  tenant never shows a misleading "wird steuerfrei berechnet" preview for
  VAT that was never going to be charged either way.
- **On-demand invoice/Stornorechnung/Gutschrift downloads**
  (`api/account/orders/[orderNumber]/invoice/route.ts` and its
  `correction-invoice` sibling) thread `order.kleinunternehmer` through to
  `@einfach-produktiv/invoicing`'s renderers the same way they already
  thread `vatExempt`.
- **`app/company-settings-preview`'s Live Preview** merges the live-edited
  `kleinunternehmer` checkbox onto the fixed `SAMPLE_INVOICE_ORDER` before
  rendering (`kleinunternehmer` lives on `InvoiceOrder`, not
  `InvoiceSeller` — see the invoicing package's own README on why), so an
  admin sees the §19 UStG notice appear/disappear live as they toggle the
  field, without this preview needing its own separate mechanism.

### Company Settings & Live Preview

`company-settings` has a Live Preview button too, like `email-templates`
— but instead of an HTML page, it's a **live, in-browser rendered PDF**:
opening the document in the Payload admin shows the actual invoice layout
updating as the admin edits `sellerName`/address/`taxRatePercent`/
`bankName`/`iban`/`bic`, no save required.

- **`app/company-settings-preview/page.tsx`** + **`components/LiveCompanySettingsPreviewClient.tsx`**
  — same entrypoint pattern as `/email-preview/[type]` (Draft Mode via
  `app/api/preview/route.ts`), but no `[type]` segment — there's only one
  kind of document here, unlike the 10 email types. **Actually gated on
  `draftMode().isEnabled`** (calls `notFound()` otherwise), unlike
  `/email-preview` — this data includes a real bank IBAN/address once
  filled in, not just marketing email copy, so it must not render for an
  unauthenticated visitor who happens to find the URL.
- **`@react-pdf/renderer`'s `<PDFViewer>`** (not `renderToBuffer()`) is
  what makes this a *live* preview rather than a static download — it's a
  browser-only component that renders a `Document` straight into an
  embedded PDF viewer `<iframe>`, re-rendering whenever its props change.
  Paired with `useLivePreview()`'s live `data` (same postMessage mechanism
  as the email templates preview), editing a field in the admin re-renders
  the actual PDF in real time — no server round-trip per keystroke.
  Dynamically imported with `{ ssr: false }` (`next/dynamic`) since it
  touches the DOM directly; the HTML-string email previews elsewhere don't
  need that since they're just `dangerouslySetInnerHTML`.
- Renders `InvoiceDocument` (exported from `@einfach-produktiv/invoicing`
  specifically for this — everywhere else only the async
  `renderInvoicePdf()` buffer-generator is used) against a fixed
  `SAMPLE_INVOICE_ORDER` (also exported from that same package) — same "no
  real document to preview against generically" reasoning as
  `email-templates`' own `SAMPLE_ORDER`.
- No draft/published distinction here, unlike `email-templates`:
  `company-settings` has no content-versioning concept, it's just the
  current row — the page's initial (pre-postMessage) fetch is the same
  live data `getCompanySettings()` always returns.

## Newsletter signup & Brevo sync

Four separate signup entry points across the site — the shared
`Newsletter` panel (`app/components/Newsletter.tsx`, reused on Home and
`/newsletter`), `NewsletterModal.tsx` (the Navbar's "Newsletter" CTA),
`/newsletter`'s own inline hero form
(`app/newsletter/components/WeeklyImpulsesHero.tsx`), and `/challenge`'s
`EmailCapture` (`app/challenge/components/EmailCapture.tsx`) — plus
checkout's `newsletterOptIn` checkbox — all sync to Brevo's contact list.

- **`app/lib/brevo.ts`** — the only thing that talks to Brevo.
  `upsertNewsletterContact(email, source)` calls Brevo's
  **double opt-in** endpoint, `POST /contacts/doubleOptinConfirmation` —
  this only ever *requests* a subscription; Brevo sends a confirmation
  email (the template at
  `BREVO_DOUBLE_OPTIN_TEMPLATE_ID`, configured as the list's Double Opt-in
  template in Brevo's own UI) and only actually adds the contact to
  `BREVO_LIST_ID` once they click through. `source` (`"checkout"` |
  `"newsletter-page"` | `"newsletter-modal"` | `"newsletter-hero"` |
  `"challenge"`) is stored as the contact's `OPT_IN_SOURCE` attribute for
  segmentation — that attribute has to already exist on the Brevo account
  (`POST /v3/contacts/attributes/normal/OPT_IN_SOURCE`) or Brevo silently
  drops it on every request (no error at all, just never stored) rather
  than rejecting the request. `redirectionUrl` (where Brevo sends the
  contact after they click confirm) defaults to `/newsletter-confirmed`
  via `BREVO_DOI_REDIRECT_URL` — a static confirmation page
  (`app/newsletter-confirmed/page.tsx`), same visual language as
  `/bestellbestaetigung` (brand-tinted circular checkmark, serif display
  heading, thin brand divider). No query params to read — Brevo's
  redirect carries nothing this page needs, unlike `/checkout/verarbeitung`
  which polls actual payment status.
- **Already-subscribed detection** — `doubleOptinConfirmation`
  itself gives no way to tell a brand-new signup apart from an
  already-confirmed contact re-submitting the form (verified directly:
  calling it twice for the same confirmed contact returns the identical
  `201` both times, just silently resends the confirmation mail). So
  `upsertNewsletterContact()` checks first via `GET /v3/contacts/{email}`
  — a contact's `listIds` on Brevo is only populated once double opt-in
  actually confirms, never for a merely-requested one, so its presence is
  a reliable signal. If already subscribed: skips the resend entirely and
  returns `{ ok: true, alreadySubscribed: true }` instead. The check fails
  open (any error → proceed to the normal signup flow) — it's a UX
  nicety, never a reason to block a real signup. **Routed through the
  existing error state, not a success variant** — the form stays visible
  with a small red note below it, exactly like every other inline
  validation error (`useNewsletterSignup.ts` sets `status: "error"`,
  `error: "Diese E-Mail-Adresse ist schon für unseren Newsletter
  angemeldet."`). This error clears on the next interaction
  (`handleEmailChange`/`handleConsentChange` both call a shared
  `clearSubmitError()`), matching standard form-validation behavior
  instead of sitting there until the next submit.
- **`app/lib/useNewsletterSignup.ts`** — the shared email/consent/submit
  state + on-blur validation + refocus-on-invalid-submit behind all four
  forms. Each form keeps its own markup/visual style (`Newsletter`'s
  panel layout, `/challenge`'s hardcoded-hex-color palette, etc.) — only
  the logic is shared, not a one-size-fits-all component; the
  real-success message text (`successMessage`) also lives here rather
  than hardcoded per form.
- `/api/newsletter/subscribe/route.ts` logs `upsertNewsletterContact()`'s
  real failure `reason` server-side (`console.error`) while keeping the
  customer-facing error generic ("Anmeldung ist fehlgeschlagen...") —
  never leaks Brevo's internal error text, but stays diagnosable from the
  server logs (e.g. a misconfigured `BREVO_LIST_ID`).
- **`app/lib/email.ts`** — `isValidEmail()`/`validateEmailFormat()`,
  the single plain-email-format check shared by every newsletter form
  *and* checkout's own email field.
- **`app/api/newsletter/subscribe/route.ts`** — validates
  email-format + consent server-side too (never trusts the client alone),
  then calls `upsertNewsletterContact()`.
- Checkout's sync (`app/api/checkout/route.ts`) is fire-and-forget
  alongside the order-confirmation email — a failed marketing sync must
  never fail checkout, and isn't worth a critical alert either (nothing
  customer-facing depends on it).
- **This app never sends marketing/campaign mail itself** — only
  transactional (order confirmation, password reset, status updates).
  Whatever automation Brevo has configured on the list (a "Welcome Flow"
  etc.) runs entirely on Brevo's own side once a contact lands there;
  Brevo's Automation workflows aren't exposed via their public REST API
  at all, so that piece can only be built/inspected in Brevo's own UI, not
  from this codebase.
- Needs `BREVO_API_KEY`/`BREVO_LIST_ID` set in the deployment environment,
  plus `BREVO_DOUBLE_OPTIN_TEMPLATE_ID` (no safe default — every signup
  silently no-ops without it) and optionally `BREVO_DOI_REDIRECT_URL`.
- **`NewsletterModal.tsx`'s left photo** stretches (`items-stretch`,
  `md:aspect-auto`) to match the right column's height — the
  emailError/already-subscribed messages are always rendered with a
  reserved `min-h-[1.05rem]` (never conditionally mounted), so toggling
  them never changes the column's height, and the photo never resizes
  along with it.

## Orders & customer accounts

An account is required to buy — there is no guest checkout. Registration
happens inline in `/checkout`'s "1. Rechnungsadresse" card (a password
field appears there when nobody's logged in), or standalone via
`/konto/registrieren` (`RegisterForm.tsx`, reusing the same
`/api/account/register` route) for a visitor who wants an account
independent of a purchase (e.g. to use the wishlist, see below). There's
no persistent "already a customer? log in" prompt shown to every
logged-out visitor regardless of relevance — instead, the checkout email
field's `onBlur` calls `/api/account/check-email`
(`checkEmailExists()` in `customerAuth.ts`, service-secret authenticated —
Customers isn't public-read) and only *then* swaps Card 1's own
"Passwort (für dein neues Konto)" field out for an inline login prompt
(password field + "Einloggen" button), rendered right under the same
email field the shopper just typed into rather than asking for it a
second time in a separate field — a `useEffect` scrolls it into view if
needed. `handleSubmit`'s own `emailExists` handling (see "Checkout
registration collisions" below) is the fallback for the case this check
was skipped or raced. `LoginForm.tsx` honors an optional `?redirect=`
param (used by the wishlist's login-gate, see below), landing back on
whatever page sent the visitor to log in instead of always
`/konto/bestellungen`.

- **`app/lib/customerAuth.ts`** (server-only) is the single place that
  talks to Payload's `customers` collection — a second, fully separate
  `auth: true` collection from any admin login, existing purely for this
  storefront's own accounts. Payload issues a JWT on register/login; this
  app never relies on Payload's own auth cookie (different origin —
  `einfach-produktiv.mk360.de` vs `payload.mk360.de`) and instead mints its
  **own** httpOnly `ep_customer_token` cookie holding that JWT, forwarded
  as an `Authorization: JWT <token>` header on every subsequent Payload
  call.
- **`app/api/account/*`** — thin route handlers around `customerAuth.ts`:
  `register`, `login`, `logout`, `me`, `orders` (list), `profile`
  (GET/PATCH incl. the one saved default address), `password` (verifies
  the current password via a real login attempt before changing it,
  doesn't just trust the caller), `cart` (GET/POST, see below),
  `verify-email`, `resend-verification`, `delete`, `export` (see "Email
  verification" and "GDPR self-service" below), `forgot-password`,
  `reset-password` (see "Password reset" below),
  `orders/[orderNumber]` (PATCH — cancel/return-request, see "Order
  cancellation & returns" below), and `orders/[orderNumber]/invoice`
  (GET — invoice PDF download, see "Invoice PDFs" below).
- **`app/konto/components/KontoShell.tsx`** is the shared shell for every
  logged-in `/konto/*` page (bestellungen, merkliste, profil) —
  `AccountNav.tsx` (persistent sidebar on `sm:`+, a horizontal tab bar
  below it) plus the `<main>`/`<Footer>` wrapping used to be duplicated
  per page, with the equivalent of the nav buried as plain links at the
  bottom of the orders list (unreachable once that list got long). Each
  page still owns its own auth-check/redirect/data-fetching and renders
  its own heading; right under that heading it renders
  `AccountIdentity.tsx` ("Eingeloggt als …, Kundennummer …") so that line
  looks identical on every page without `KontoShell` itself needing to
  know each page's title. `AccountNav` also renders the "Abmelden"
  button (logout, folded into the nav rather than living at the bottom of
  a specific page).
- **`/konto/bestellungen`** lists a customer's own orders — a per-card CSS
  Grid (`grid grid-cols-2 min-[500px]:grid-cols-4`, so every card's
  Bestellnummer/Datum/Artikel/Status/Zahlungsstatus/Gesamtbetrag fields
  line up at identical x-positions regardless of label width, dropping to
  2 columns below 500px), status shown as a colored `OrderStatusBadge.tsx`
  plus a `PaymentStatusBadge.tsx` (Offen/Bezahlt/…, in the same
  red/subtle-background style as a failed fulfillment status when unpaid);
  optional status/paymentStatus/year filters (`OrderFilters.tsx`, 3
  `CustomSelect` dropdowns, URL-search-param-driven, collapsed behind a
  "Filter" toggle below `sm:`) when the tenant's `orderFilterEnabled`
  toggle is on (see "Feature toggles" below). **`/konto/bestellungen/[orderNumber]`**
  shows one order's full detail (items, address, totals, `status`, plus
  companyName/VAT-ID and a VAT-exemption note when the order has them). A
  "Zahlungsart ändern" button appears when an order is still unpaid
  Überweisung and an active Stripe payment method exists — reuses the same
  Stripe `PaymentStep`/`/checkout/verarbeitung` polling flow checkout
  itself uses (via a `returnContext`/`context` prop so confirmation lands
  back on the order page instead of `/bestellbestaetigung`), and sends
  `sendPaymentSwitchedEmail()` (`lib/orderEmail.ts`) instead of the usual
  order-confirmation mail once payment confirms — same shape as the
  status-change emails, but re-attaches a freshly generated invoice PDF
  (same `invoiceNumber`, never re-issued) now marked "Bereits beglichen"
  instead of showing the Vorkasse notice. `status`
  (`received` → `processing` → `shipped` → `delivered`, plus
  `cancelled`/`return_requested`/`returned`) is maintained by hand in the
  Payload admin for the shipping states — no shipping-carrier API
  integration.
- **A `cancelled` Stripe order with no `invoiceNumber` never shows up
  here** — that's a `pending_payment` order whose payment failed or timed
  out (see the backend's `expirePendingPayments`/`confirmPayment.ts`), not
  a real Storno (which is always of an already-`received`, already-
  invoiced order, so it always has an `invoiceNumber`). From the
  customer's point of view a payment that never went through was never
  really an order, so `getCustomerOrders`/`getCustomerOrderDetail`
  (`app/lib/customerAuth.ts`) filter these out by default — the row still
  exists in Payload for admin/audit purposes (shown there as "Zahlung
  fehlgeschlagen", see the backend's own README), just not surfaced to
  the customer. `getCustomerOrderDetail` takes this as an **optional**
  4th param, defaulting `false` — `/api/checkout/status/route.ts`'s
  post-payment polling deliberately calls it unfiltered, since that flow
  needs to keep seeing exactly this order (to show "Zahlung
  fehlgeschlagen, bitte erneut versuchen") for the one case this filter
  would otherwise hide. `/api/account/export/route.ts`'s GDPR export also
  opts out (`false`) — a legal completeness export can't silently drop
  rows.
- **`Navbar.tsx`'s `AccountLink`** (account icon, always visible in the
  header itself — not duplicated inside the mobile fullscreen menu, see
  "Mobile navigation" below) is the only *always*-reachable way into
  `/konto/*` — added after discovering there previously wasn't one:
  `/checkout`'s own login toggle only renders once the cart already has
  items (its empty-cart state is an early return with no such toggle), and
  `/bestellbestaetigung`'s "Meine Bestellungen ansehen" link only exists
  after a completed order. A returning customer with an empty cart and no
  recent order had no way to reach the login page at all before this.
  Fetches auth state client-side via `/api/account/me` (not through the
  server-rendered root layout) specifically so `app/layout.tsx` — otherwise
  static/ISR-cacheable — doesn't get forced into per-request dynamic
  rendering just to know one icon's href; briefly shows the logged-out
  state on first paint until that fetch resolves. Re-fetches on an
  `ep-auth-changed` `window` event (`app/lib/auth.ts`'s `dispatchAuthChanged()`,
  called by every login/logout/checkout-registration call site) — the icon
  otherwise never noticed a login/logout until a hard reload, since
  `router.refresh()` only re-runs Server Components, not an
  already-mounted Client Component's effects, and this Navbar lives in the
  root layout and never unmounts across navigations. The icon itself also
  gets a small brand-colored underline while logged in — same visual
  language as the desktop nav links' active-state indicator — since the
  icon alone doesn't otherwise signal session state at a glance.

### Feature toggles

A handful of features are gated behind `CompanySettings` booleans
(Payload admin → Company Settings → **Features** tab): `wishlistEnabled`,
`searchEnabled`, `shopFilterEnabled`, `blogFilterEnabled`,
`orderFilterEnabled`. Each stays entirely invisible in the frontend —
no icon, no filter UI, no route reachable — until its toggle is switched
on; if a feature "isn't showing," check that setting first.

### Wishlist

Backend `wishlist-items` collection (customer + product + optional
variant, unique per combination, customer-scoped access — see the
Payload backend's own README). Frontend: `useWishlist.ts` (a fetch-based
hook with an optimistic toggle + a `window` event so every
`WishlistButton`/the Navbar badge stay in sync — not `localStorage`-backed
like the cart, since a wishlist needs a logged-in customer to mean
anything), `WishlistButton.tsx` (heart icon, redirects to login with
`?redirect=` if logged out), the Navbar's heart icon + count badge
(hidden below `sm:` — Account+Cart are the only always-visible icons on
true mobile, to avoid crowding the nav), and `/konto/merkliste`
(`MerklisteGrid.tsx`, a Client Component grid so removing an item
disappears immediately). `Product` carries a `numericId` field (the raw
Payload id) alongside its slug-based `id`, since `wishlist-items.product`
is a real numeric relationship, unlike the cart/checkout's slug-keyed
"commerce id".

Buying a wishlisted item never auto-removes it — a customer often
wishlists something specifically to buy it again (gifts, repurchases).
Instead `/konto/merkliste` marks it: dimmed image + a "Gekauft am [date]"
badge (replacing the "Ausverkauft" badge when both would apply). Removal
stays entirely manual via the same `WishlistButton`.
`WishlistItem.purchasedAt` (`app/lib/customerAuth.ts`) is never persisted
on the backend collection — it's derived fresh on every `getWishlist()`
call by cross-referencing the customer's own orders
(`getPurchasedVariantMap()`), matched on the exact `(product, variant)`
pair, excluding `cancelled`/`returned` orders.

### Search & filters

**Instant search** — `/api/search` runs plain Payload
`where[...][contains]` queries (Postgres `ILIKE`) against Products +
Posts, not a dedicated search index; `SearchOverlay.tsx` (debounced
250ms, grouped results) plus a Navbar search icon (same `hidden sm:`
treatment as the wishlist icon).

**Filters** are URL-search-param-driven everywhere (shareable/bookmarkable,
no client-side-only state): `/konto/bestellungen`'s status/paymentStatus/year
dropdowns (`OrderFilters.tsx`, `CustomSelect.tsx`); `/blog`'s category
toggle chips (`BlogCategoryFilter.tsx` — a Client Component using
`useRouter()` + `useTransition()`, chips disabled while a navigation is
pending so rapid clicks can't fire overlapping RSC navigations that
commit out of order); `/shop`'s left sidebar (`lg:+`) / filter bar
(`<lg`, both rendered by `ProductGrid.tsx`) — a dual-handle price range
slider (`PriceRangeFilter.tsx`, drag-to-filter, commits on release not
per drag-frame), category checkboxes (`CategoryFilter.tsx`, union match
— a product with no category tagged still matches every filter rather
than disappearing, see `Product.categories`' own comment in
`lib/payload.ts`), and a "Nur verfügbare Produkte" availability toggle
(same component). Sidebar styled to match `AccountNav.tsx`'s label/
spacing treatment. Both `/blog` and `/shop`'s grids key their
`RevealGroup` on the actually-rendered item set — `whileInView` only
fires once per component instance, and a filter change re-renders the
same page in place rather than remounting it, so without the key a
freshly filtered list could mount into an already-settled `RevealGroup`
and stay stuck at `opacity: 0` (reported as the grid "going blank"
after filtering).
**`CustomSelect.tsx`** (`app/components/`) is a fully custom-styled
dropdown (own trigger + `role="listbox"` panel, keyboard nav,
click-outside-to-close) used wherever a native `<select>`'s un-stylable
options popup would look off-brand — also used for checkout's two
country pickers.

### Mobile navigation

Below `lg` (1024px), the hamburger opens a **fullscreen** panel
(`Navbar.tsx`, `motion.div` from the `motion/react` package already used
elsewhere in this app for `NewsletterModal`/`VersandModal`) — not an
in-flow accordion pushed under the header like before. A circular
`clip-path` reveal (`circle(0vmax at 100% 0%)` → `circle(150vmax at 100%
0%)`, `vmax` rather than `%` so full coverage holds regardless of aspect
ratio) expands from the hamburger's own top-right corner, sweeping toward
the opposite corner last. Nav links fade/rise in with a per-item stagger
once the reveal has visibly opened up. The panel is a **sibling** of
`<header>`, not a child — `mobileOpen` gives the header its own
`backdrop-blur`, which would make it a new CSS containing block for any
`position: fixed` descendant and break the panel's fixed-to-viewport
positioning (same class of bug documented on `NewsletterModal`). No
login/account CTA inside the panel — that's reachable via the account icon
in the header itself, which stays visible above the panel throughout.
- **Checkout registration collisions**: if the email typed into Card 1
  during inline registration already belongs to an existing account,
  Payload's create call fails — `registerCustomer()` in `customerAuth.ts`
  detects this specifically (`emailExists: true` on the returned
  `AuthResult`, inferred from the field flagged in Payload's validation
  error, since Payload's own message text doesn't distinguish "duplicate"
  from other email-field failures) rather than just surfacing a generic
  error. `CheckoutContent.tsx`'s `handleSubmit` reacts by switching
  `showLogin` on (same inline prompt described above — reuses Card 1's
  own email field, nothing to pre-fill) and scrolling it into view via a
  `useEffect`, instead of leaving the customer stuck with an error and no
  obvious next step. `handleLogin()` itself posts the live `email` field
  value, not a separate `loginEmail` state — there's only ever one email
  input on this form now.
- **`/konto/profil`** edits name + the one saved default address (deliberately
  a single address, not a full address book — see the assistant's memory
  note on optionally expanding this later), changes the password, shows
  the email-verification banner, and has the GDPR export/delete section.
  Its "Land" `<select>` shares the same Payload-configurable country list
  `/checkout` reads (`ProfileForm.tsx` takes a `shippingCountries` prop,
  `page.tsx` fetches `getShippingCountries()`), so a country added/removed
  in the admin reaches both places.
- **Cart sync**: `app/components/CartSync.tsx` (mounted once in
  `app/layout.tsx`) watches the local cart via `useCart()` and
  debounce-POSTs it to `/api/account/cart` on every change; the route
  401s (silently, by design) when nobody's logged in. On login
  (`LoginForm.tsx`, and `CheckoutContent.tsx`'s inline toggle),
  `mergeServerCartIntoLocal()` (`app/lib/cart.ts`) folds whatever was
  saved server-side into the local cart by quantity — CartSync's own
  effect then pushes the merged result back up on its own, so there's no
  separate explicit "save after merge" call.
- Still out of scope: a full address book (single default address only —
  see the assistant's memory note), single-currency.

### Rate limiting

`app/lib/rateLimit.ts` — an in-memory, per-IP sliding-window limiter
(`checkRateLimit(key, {limit, windowMs})`), deliberately no Redis: this
app runs as a single Coolify container, so a plain `Map` is enough and
needs no new infra. Resets on redeploy/restart — acceptable at this
shop's traffic level; revisit with a shared store if this ever scales to
multiple instances. Applied (keyed by `X-Forwarded-For`, which Caddy
already sets) to `/api/account/register`, `/api/account/login`,
`/api/account/password`, and `/api/account/resend-verification`.

This complements, not replaces, Payload's own **per-account** login
lockout (`customers.auth`, `maxLoginAttempts: 5` / `lockTime: 10min`,
Payload defaults — see the Payload README's "Login rate limiting"
section) — that stops brute-forcing one known email, this stops an IP
spraying attempts across many, or hammering registration.

### Session refresh

`proxy.ts` (project root — Next.js 16 renamed `middleware.ts` to
`proxy.ts`; see `node_modules/next/dist/docs/01-app/03-api-reference/03-file-conventions/proxy.md`
if this ever looks wrong against older docs/training data). Runs on
`/checkout`, `/konto/*`, `/api/account/*`. Decodes (not verifies — Payload
verifies for real on every actual API call) the `ep_customer_token`
cookie's JWT `exp` claim; if less than 15 minutes remain, silently calls
Payload's built-in `POST /api/customers/refresh-token` and swaps in the
refreshed token. Net effect: an actively-browsing customer never gets
logged out mid-session, but someone who walks away is logged out within
~2h of their last request (Payload's `tokenExpiration` default, unchanged
on the Payload side).

### Email verification

Non-blocking by design — see the Payload README's `customers.emailVerified`
section for why this is a custom flag rather than Payload's built-in
`auth.verify: true` (short version: that would hard-block login for a
brand-new customer trying to finish the purchase they just registered
mid-checkout for). The initial email is sent by Payload itself (an
`afterChange` hook on `customers`, fires on create). `/konto/profil`'s
`VerificationBanner.tsx` shows a non-blocking "bitte bestätigen" hint with
a resend link when `!profile.emailVerified`; resending
(`/api/account/resend-verification`) is sent directly from this app
instead (`app/lib/alertAdmin.ts`'s `sendVerificationEmail()` — same
Hostinger SMTP, no Payload hook to piggyback on for a plain field update).

### Password reset

Unlike email verification, this needed no custom flag — `forgotPassword`
doesn't block login, so it's Payload's built-in flow as-is (see the
Payload README's `customers.auth.forgotPassword` section), just with the
email content/destination swapped so the link points here instead of the
Payload admin. `/konto/passwort-vergessen` (`ForgotPasswordForm.tsx`) →
`POST /api/account/forgot-password` → always responds `{ok:true}`
regardless of whether the email exists (same anti-enumeration reasoning as
Payload's own operation — the route must not leak a different response
shape for "no such account", see its own comment). `/konto/passwort-zuruecksetzen?token=...`
(`ResetPasswordForm.tsx`, token read server-side from `searchParams` —
avoids needing a `<Suspense>` boundary, unlike the `?code=` cart case
above which genuinely needs client-side `useSearchParams()`) →
`POST /api/account/reset-password` → Payload logs the customer in on a
successful reset (returns the same `{token, user}` shape as login), so the
session cookie is set immediately, no separate login step. `LoginForm.tsx`
links to `/konto/passwort-vergessen`.

### Email templates & Live Preview

All 10 transactional emails (order confirmation, password reset, the
payment-method-switched email, and the 7 order-status-change types below)
read their subject/heading/body/footer wording from Payload's `email-templates`
collection — editable in the admin without a deploy, with a Live Preview
button using the exact same mechanism as Posts/LegalPages/Testimonials
(`useLivePreview()` from `@payloadcms/live-preview-react`, already a
dependency here for `LivePostContent.tsx`).

**Live Preview only reliably updates when popped out into its own
browser tab/window, not in the embedded admin panel.** Root cause: the
preview goes through `buildPreviewUrl()` on the Payload side, which hits
`/api/preview` on this frontend's own origin to enable Next.js Draft
Mode via a cookie — but admin (`payload.mk360.de`) and frontend
(`einfach-produktiv.mk360.de`) are different origins, so from inside the
admin's embedded `<iframe>` that's a cross-site/third-party context.
Modern browsers (Safari by default, Chrome/Firefox increasingly)
block or partition cookies set inside a cross-site iframe regardless of
which domain actually issued them, so the Draft Mode cookie doesn't
reliably persist there. Once popped into its own window it's a top-level
navigation, not a third-party context, so the cookie sets normally and
everything works. Affects every Live-Preview-enabled collection in this
system (Posts/LegalPages/Testimonials too), not just email templates —
a structural consequence of running admin and frontend on separate
domains, not something fixable at the collection-config level. A real
fix would mean serving both under one domain (reverse proxy path) rather
than two subdomains.

- **`app/lib/emailTemplates.ts`** — pure string-building functions
  (`renderOrderConfirmationHtml()`, `renderPasswordResetHtml()`,
  `renderOrderStatusHtml()`), no server-only or client-only imports. Used
  **both** server-side for the real send (`orderEmail.ts`) **and**
  client-side for the Live Preview page — same function, same inputs, so a
  Live Preview edit and the real sent email are guaranteed to render
  identically for order-confirmation and payment-method-switched, the
  only two of the 10 actually sent from this repo (password-reset and all
  7 order-lifecycle types are sent by Payload itself, using its own
  inline templates — see that repo's README for why — so their Live
  Previews approximate rather than pixel-match).
  Inline-styled HTML (`<table>` layout, `style` attributes, no
  Tailwind/`<style>` block) — most email clients strip external/embedded
  CSS.
- **`/email-preview/[type]/page.tsx`** — entered exclusively from Payload's
  admin iframe (`EmailTemplates.ts`'s `admin.livePreview.url`), never a
  real visitor destination (`noindex`). Always reads with `draft: true` so
  an unsaved admin edit shows immediately. Renders against **sample data**
  (`SAMPLE_ORDER`/`SAMPLE_ORDER_MANUAL` in `emailTemplates.ts`, toggleable —
  the two fixtures cover both the paid and the Vorkasse/Überweisung
  branches) — unlike the other three Live Preview targets, there's no
  "current" real order/reset-link to preview against generically. Renders
  the email HTML inside an `<iframe srcDoc>` rather than
  `dangerouslySetInnerHTML` directly into the page, so the email's own
  `<body>...</body>` fragment gets its own real document context instead
  of nesting invalid HTML inside this page's `<body>`.
- The *real* send always reads the **published** template
  (`getEmailTemplate()` in `app/lib/payload.ts`, `draft` unset) — a Live
  Preview edit never affects a live customer email until actually saved.
- **`active` toggle** — each row has an `active`
  checkbox (backend `EmailTemplates.ts`); off suppresses the send
  entirely, checked here for `order-confirmation`
  (`orderEmail.ts`'s `sendOrderConfirmationEmail()`) before the hardcoded
  default-wording fallback ever applies. See the backend repo's own
  README ("Email templates: active/inactive toggle") for the full
  picture, including the `password-reset` exception (Payload's core
  `forgotPassword` operation has no hook to actually cancel that send).
- `npx payload run src/seed-email-templates.ts` (Payload repo) seeds
  defaults for all 10 rows — deliberately on-brand and a little playful
  ("Bestellt!" / "Kein Drama." / "Unterwegs!" / "Storniert." / "Alles
  klar." / "Alles erledigt.", not generic transactional-email
  boilerplate), matching this site's voice elsewhere (see e.g. the
  testimonial copy). Two intentional exceptions to that voice: the
  email-verification mail (Payload-side, plain functional copy — see that
  README) and the Stornorechnung/Gutschrift PDFs (formal legal documents,
  no brand voice by design). Editable in the admin afterward regardless.
  `sendOrderConfirmationEmail()` also has a hardcoded fallback for the
  rare case a fresh install's order arrives before that seed has run.
- **`emailShell()`'s visual design deliberately echoes `/bestellbestaetigung`**
  (the on-screen order confirmation page) rather than reading as a generic
  transactional email: same warm cream background/brand color as
  `globals.css`'s `--color-*` tokens (hardcoded here as literal hex — email
  clients don't resolve `var()` either), a circular brand-tinted icon
  (✓ for order-confirmation, ✉ for password-reset) echoing that page's own
  success-icon treatment, a thin brand-colored divider under the heading,
  and a Georgia/serif heading font as the closest reliably-available
  approximation of the site's Playfair Display (most email clients strip
  `@font-face`/external font requests, so an actual web font isn't an
  option here). Not shared code with the React page — this is plain
  inline-styled HTML built for email-client compatibility (nested
  `<table>`s, no flexbox) — just matched by eye.
- **Footer carries a full legal Anbieterkennzeichnung, not just a brand
  line.** `emailShell()` takes a `footerLines: string[]` array built by
  `buildLegalFooterLines(seller)` — `sellerName`, `sellerStreet`,
  `sellerZip`/`sellerCity` (+ `sellerCountry` if not Germany), `E-Mail:
  sellerEmail`, and `USt-IdNr.: vatId` when set — the same admin-editable
  `company-settings` fields the invoice PDFs already use, rather than a
  literal `"einfach produktiv · admin@mk360.de"` string. `orderEmail.ts`
  and `alertAdmin.ts` (both the resend-verification mail and the plain-text
  critical-alert mail) all fetch `company-settings` once
  (`getSellerForInvoice()`) and pass the `seller` object straight into the
  render functions, which call `buildLegalFooterLines()` themselves — one
  place composes the footer, not each call site. The Payload-side sends
  (password-reset, the 7 order-lifecycle emails, the *initial*
  verification email) get the equivalent treatment via that repo's own
  `src/lib/sellerInfo.ts`'s `buildLegalFooterLines()`/`getSellerFooterLines()`
  — see that repo's README for its own copy of this section. Live Preview
  passes `seller: null`, which falls back to `DEFAULT_LEGAL_FOOTER_LINES` (a
  placeholder Anbieterkennzeichnung) since there's no real order/tenant
  context there to fetch against. Note `company-settings` currently has no
  Handelsregister court/number or Geschäftsführer field — fine for a sole
  proprietorship, but would need adding if the business becomes a
  registered legal form (GmbH etc.), see that collection's own field list
  above.
- **`From` display name is dynamic (`seller.sellerName`), the address
  itself stays `admin@mk360.de`.** `Reply-To` is set to `seller.sellerEmail`
  so a customer's reply actually reaches the seller regardless of the From
  address. The address isn't also switched to `sellerEmail` because that
  domain isn't confirmed SPF-authorized on the Hostinger account backing
  `admin@mk360.de` yet — doing so without that confirmation risks
  order-confirmation/verification mail landing in spam or bouncing outright.
  Both `orderEmail.ts` and `alertAdmin.ts`'s `sendVerificationEmail` set
  this the same way; `sendCriticalAlert` (internal, admin@mk360.de to
  itself) doesn't need it.

### GDPR self-service

`/konto/profil`'s "Konto & Daten" section:
- **Export** (`/api/account/export`, GET) — profile + every order's full
  detail as one downloadable JSON (`Content-Disposition: attachment`).
  Genuinely complete, not a summary — Art. 20 data portability.
- **Delete** (`/api/account/delete`, POST, password re-verified via a real
  login attempt first) — deletes the `customers` document. Past orders
  are **not** touched: `orders.customer` is `ON DELETE SET NULL` in
  Payload, so an order keeps its own name/address/items snapshot (already
  stored independently for exactly this kind of reason) for tax-retention
  purposes (§147 AO / GDPR Art. 17(3)(b) explicitly permits this) — only
  the account/login itself disappears. The UI says this explicitly before
  deleting, not as a surprise afterward.

### Order cancellation & returns

`/konto/bestellungen/[orderNumber]` shows one self-service button when
applicable: "Bestellung stornieren" while `status === 'received'`, or
"Rücksendung anfragen" while `status` is `'shipped'` or `'delivered'`
(`customerOrderAction()` in `customerAuth.ts` decides which, if any).
Posts to `/api/account/orders/[orderNumber]` (PATCH), which re-checks the
transition is still valid (friendlier error than a bare 403 if it's gone
stale — two tabs open, order shipped in the meantime) before calling
`requestOrderStatusChange()`.

Requesting a return opens an inline form (`OrderActionButton.tsx`), not
just a confirm dialog — **partial returns are supported**: a quantity
input per order line (0 up to that line's ordered quantity) plus a
required reason textarea. At least one line must have a nonzero quantity
to submit. Cancel stays a plain `window.confirm()` — it's a lower-stakes,
whole-order-only action (before shipping, often just a change of mind),
no quantity picker or reason needed there.

The route (`/api/account/orders/[orderNumber]` PATCH) reconstructs the
order's *full* `items` array before sending it to Payload — only the
requested lines' `returnQuantity` differs from what's already stored,
every other field (product/price/tax rate/etc.) is passed through
unchanged. This isn't optional: Payload's array field expects every
required sub-field present on each row, and the field-lock hook (see
below) specifically checks that only `returnQuantity` changed — a sparse
`{ returnQuantity: 2 }`-only patch would fail both.

**The real security boundary is in Payload**, not here: `orders.access.update`
already scoped a customer's JWT to their own order, but with no
field-level restriction — before this stage, a logged-in customer could in
principle PATCH *any* field of their own order (`total`, `items`,
anything), just because nothing in the frontend had ever exercised that
path yet. `Orders.ts`'s `beforeChange` hook rejects a customer-authenticated
update unless the change is limited to `status` (plus `returnReason` and
each item's `returnQuantity`, bounded 0..quantity, alongside a
`return_requested` transition), via an allowed transition. See the
Payload README's own writeup for the full detail — including
`orderUpdateValidation.ts`, where this logic now lives as a unit-tested
pure function.

No hard 14-day return-window check in code (no separately tracked delivery
date exists yet) — relies on the existing `/widerruf` legal text plus
manual admin review. No automatic refund (no payment provider exists yet)
— a return/cancellation request is just captured structurally instead of
arriving by email/phone; the admin still processes it by hand in the
Payload admin.

Reaching `status: 'cancelled'` or `status: 'returned'` also auto-generates
a **Stornorechnung**/**Gutschrift** correction-invoice PDF, attached to
that status's customer email (Payload-side, see the Payload README's "How
a Stornorechnung/Gutschrift relates to the original invoice" section —
this is not frontend code). Stornorechnung is always a full reversal
(cancellation is always pre-shipping, whole order, shipping included).
Gutschrift reflects only the returned quantities — full or partial —
**excludes shipping** (already delivered by the time a return is
possible) and **never reprorates the original discount** (confirmed
policy, not a default: the discount stays with whatever's kept). Either
way, this is a document only, not a money movement: an actual refund
still has to happen manually, since no payment provider exists yet to
capture or reverse a real charge.

### Status-change emails

Several `orders` lifecycle events trigger a customer email — the
`status` transitions `shipped`/`cancelled`/`return_requested`/`returned`/
`delivered`, plus a tracking number being added or corrected
(`order-tracking-added`/`order-tracking-corrected`) — not
`processing`/`received`, which aren't customer-actionable. **Sent
entirely from Payload**, not this repo —
`orders.ts`'s `afterChange` hook there compares `doc.status` to
`previousDoc.status` and fires regardless of who made the change (an admin
setting `shipped`/`returned` in the Payload admin, or the customer's own
self-service cancel/return-request above land on the exact same hook). See
the Payload README's `orders.ts` section for the actual send logic,
including the Stornorechnung/Gutschrift attachment on cancelled/returned.

This repo's only involvement is the **Live Preview approximation** — same
established gap as password-reset (see below): `renderOrderStatusHtml()`
in `app/lib/emailTemplates.ts` and the corresponding entries in
`/email-preview/[type]`'s `VALID_TYPES` exist purely so an admin editing
any of these order-lifecycle rows in the `email-templates` collection
sees a reasonable preview — the actual sent HTML is Payload's own
`src/lib/emailShell.ts` render, not this file's.

### Monitoring & alerting

Base uptime (is the site/Payload reachable at all) is already covered by
existing Uptime Kuma HTTP monitors with email alerting (`monitor.mk360.de`
— see `~/dev/README.md`'s Kuma section) and isn't part of this app. What's
new here is the one failure mode Kuma structurally can't see: the site is
up, a customer completes checkout, and the order still doesn't get
persisted (`createOrder()` returns `null` in `/api/checkout/route.ts`).
That path calls `app/lib/alertAdmin.ts`'s `sendCriticalAlert()` — its own,
independent SMTP connection (same Hostinger account, but **not** routed
through Payload, since Payload being the actual problem is one of the
scenarios this needs to still report on). Fire-and-forget, its own
try/catch, never blocks or fails the actual error response the customer
sees.

`/api/health` (GET) — checks Payload's public API is actually reachable
(3s timeout), not just that this page rendered; added as a Kuma HTTP
monitor in the existing "Content & API" group (`~/dev/README.md`'s
documented `sqlite3`-insert method, Kuma 1.x has no REST API for this).

`/shop` itself also has its own Kuma HTTP monitor ("einfach-produktiv Shop
(Produkte, Varianten, Lagerbestand)", same "Content & API" group) — added
once the shop grid started doing real work at render time (`fullyOutOfStock`
across a product's variants, `effectivePrice()`), not just listing static
content; `/api/health` alone only proves Payload is reachable, not that this
specific page still renders. The Payload jobs queue's own failure monitor
(`/api/health/jobs`, `hasError: true` in the last 24h) already covers all
five scheduled jobs generically by task-agnostic query — the four added this
session (low-stock digest, stale-unverified-accounts report, weekly revenue
report, expired-discount-code cleanup) needed no monitor changes of their
own; see the Payload README's "Jobs Queue" section.

## Tests

`npm run test:unit` (Vitest, `node` environment, no jsdom/Next.js runtime
needed) — no test infrastructure existed in this repo before; started with
the pure logic most likely to silently produce wrong numbers on a live
order, not attempted exhaustive coverage:

- **`app/lib/__tests__/cartTotals.test.ts`** — subtotal/discount/shipping
  math (`computeSubtotal`, `computeCartTotals`), incl. the fixed-discount
  clamp and `compareAtPrice`-based savings display being independent of
  the discount-code math.
- **`app/lib/__tests__/bundleContents.test.ts`** — `describeBundleContents()`,
  extracted out of `app/api/checkout/route.ts` into its own module
  (`app/lib/bundleContents.ts`) specifically so it's importable from a
  test — Next.js `route.ts` files only allow HTTP-method (+ a few config)
  exports, not arbitrary named ones.

The original invoice's `isPaidImmediately()`/`groupByTaxRate()` and the
Gutschrift/Stornorechnung money math (`resolveLineItems()`,
`groupByTaxRate()`) both live in `@einfach-produktiv/invoicing` now (see
"Invoice PDFs" above), not in this repo — their tests moved with them
into that package's own `src/__tests__/`, run via that package's own
`vitest`, not this repo's `test:unit`. The Payload-side `orders.ts`
field-lock security logic is still tested in the **Payload backend's**
own `test:unit` — see that repo's README's own "Tests" section, since
that's where that logic actually lives.

## Deployment

- **Dockerfile**: 3-stage build (`deps` → `builder` → `runner`) with
  BuildKit cache mounts, producing a ~100 MB standalone image. This is the
  reference `Dockerfile` copied when scaffolding new projects on this VPS
  (see the infra repo's new-project workflow).
- Deploys via `git push` → Gitea webhook → Caddy `/deploy/einfach-produktiv`
  bridge → Coolify API → rebuild + restart. Full mechanics in
  `~/dev/README.md`.

## Related design source

- `~/dev/einfach-produktiv/mockups/` — Figma-stage mockup PNGs
- `~/dev/einfach-produktiv/styleguide.md` — design tokens (colors, type, spacing)
- `~/dev/einfach-produktiv/einfachproduktiv_figma_prompt_guide_v3.md` — Figma rebuild prompt guide
