# 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.

## 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). 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` | Customer login |
| `/konto/bestellungen`, `/konto/bestellungen/[orderNumber]` | Order history + order detail (own orders only) |
| `/konto/profil` | Profile/address editing + password change |
| `/challenge` | "Mini-Challenge" tool |
| `/todo-cards` | "Todo-Karten" tool |
| `/newsletter` | Newsletter signup |
| `/versand` | Shipping policy (timeframes, costs) |
| `/impressum`, `/datenschutz`, `/agb`, `/widerruf` | Legal pages (from Payload, see `legal-pages` below) |

## 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), `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) |
| `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`, `category` (relation to `categories`), `excerpt`, `thumbnail`, `content` (richText), `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`) |
| `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) |
| `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 numbers — one row per tenant | `customerPrefix`/`customerNext`/`customerPadding`, `orderPrefix`/`orderNext`/`orderPadding`, `invoicePrefix`/`invoiceNext`/`invoicePadding`. **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 6 transactional emails this shop sends (see "Email templates & Live Preview" and "Status-change emails" below) | `type` (`order-confirmation`/`password-reset`/`order-shipped`/`order-cancelled`/`order-return-requested`/`order-returned`), `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), `bankDetails`. **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 6 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.

- **No manual input field anymore** — the Rabattcode section on `/cart`
  (`CartContent.tsx`) only renders at all when a code is actually applied;
  there's no open "enter a code" box for every visitor (Nutzer-Entscheidung:
  less visual noise, and codes are meant to be shared as marketing links,
  not guessed/typed in). Instead, `?code=SAVE10` on the `/cart` URL
  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). A code that
  arrives via the URL but turns out invalid/expired still shows an inline
  error, just without an input box to attach it to.
- **`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.
- **`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`. `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()` — 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.
- Still not built: real payment processing — the checkout button is
  labelled "zahlungspflichtig" but nothing actually captures a payment
  yet. See `project_backend_checkout_plan` in the assistant's own memory.

### 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`.

- **`app/lib/invoicePdf.tsx`** — a `@react-pdf/renderer` `Document`
  (`InvoiceDocument`), 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 with alternating row shading, 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.
- **"Bereits beglichen" badge**: shown next to the meta boxes 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 `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).
- **Bank details**: `company-settings.bankDetails`, when set, prints in
  the footer as "Bankverbindung (für Überweisung): …" — for the case a
  customer paid (or still needs to pay) by bank transfer and needs the
  account details to do so. Currently seeded with a placeholder IBAN/BIC,
  same caveat as the rest of `company-settings`' seller data below.
- **Per-tax-rate summary**: line items are grouped by their own
  snapshotted `taxRatePercent` (see the Payload README's "Per-product tax
  rates" section) and the summary prints one "Netto (X%)" / "zzgl. X%
  MwSt." pair per distinct rate actually present in that order — a plain
  single pair in the common case (one rate for the whole order), a real
  multi-rate breakdown the moment a product with a different rate is
  involved. The order-level discount/shipping are distributed
  proportionally across each rate group before computing net/tax, so the
  grouped totals still reconcile exactly to `order.total`.
- **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).
- **`app/lib/invoiceData.ts`** — `generateInvoicePdf(order, seller)` /
  `generateCorrectionInvoicePdf(kind, order, seller)`, the render
  entrypoints every caller below goes through. `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. `app/lib/correctionInvoicePdf.tsx` is a **frontend
  port** of that same renderer (visually identical, ported not shared —
  two separate deployments, same relationship as `emailShell.ts`) used
  purely so `/konto/bestellungen/[orderNumber]` can offer a "Stornorechnung/
  Gutschrift herunterladen" download button
  (`app/api/account/orders/[orderNumber]/correction-invoice/route.ts`)
  without storing the PDF as a file anywhere: `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. Deliberately not persisted to
  disk/S3/Media — 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.
- **`company-settings`** (Payload collection, structured seller data —
  name/address/`vatId`/`taxRatePercent`/`bankDetails`) 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.

### 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`/
`bankDetails`, 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 6 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 `app/lib/invoicePdf.tsx`
  specifically for this — everywhere else only the async
  `renderInvoicePdf()` buffer-generator is used) against a fixed
  `SAMPLE_INVOICE_ORDER` — 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.

## 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). There's no persistent
"already a customer? log in" prompt — that was gendered ("Schon Kundin?")
and shown to every logged-out visitor regardless of relevance. Instead,
the 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 password field
out for an inline login form, gender-neutral copy, pre-filled with the
email just typed. `handleSubmit`'s own `emailExists` handling (see
"Checkout registration collisions" below) is the fallback for the case
this check was skipped or raced.

- **`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).
- **`/konto/bestellungen`** lists a customer's own orders (status shown as
  a colored `OrderStatusBadge.tsx`, plus an "Abmelden" link —
  `LogoutButton.tsx`); **`/konto/bestellungen/[orderNumber]`** shows one
  order's full detail (items, address, totals, `status`). `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.
- **`Navbar.tsx`'s `AccountLink`** (account icon, desktop; "Anmelden"/"Mein
  Konto" text link, mobile drawer) 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. 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.
- **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
  straight to the login toggle with that email pre-filled and
  scroll-into-view, instead of leaving the customer stuck with an error
  and no obvious next step.
- **`/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.
- **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 6 transactional emails (order confirmation, password reset, and the 4
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`).

- **`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, the only one of the 6 actually sent
  from this repo (password-reset and all 4 status-change 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` in `emailTemplates.ts`) — unlike the other three Live
  Preview targets, there's no "current" real order/reset-link to preview
  against generically.
- 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.
- `npx payload run src/seed-email-templates.ts` (Payload repo) seeds
  defaults for all 6 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 4 status-change 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

Four `orders.status` transitions trigger a customer email — `shipped`,
`cancelled`, `return_requested`, `returned` (deliberately not `delivered`,
redundant with the carrier's own notification; not `processing`/`received`,
not 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
`order-shipped`/`order-cancelled`/`order-return-requested`/`order-returned`
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).

## 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__/invoicePdf.test.ts`** — `isPaidImmediately()` and
  the original invoice's per-rate `groupByTaxRate()` (both exported via an
  `__testables` object specifically for this, same pattern the Payload
  backend uses for its own correction-invoice tests).
- **`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 Gutschrift/Stornorechnung money math itself (`resolveLineItems()`,
`groupByTaxRate()` in `correctionInvoicePdf.tsx`) and the Payload-side
`orders.ts` field-lock security logic are tested in the **Payload
backend's** own `test:unit` instead — see that repo's README's own
"Tests" section — since that's where those functions actually live (this
repo's `correctionInvoicePdf.tsx` is only a port for the download button,
not the source of truth).

## 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
