# Stripe Payment Link Creation

## Objective

Generate Stripe payment links from records without letting anyone set their own price.

A server-side generator that turns an app record into a shareable Stripe payment link, with reuse rules, reconciliation metadata, and a defined expiry.

## Before You Begin

This feature is being added to an application that already exists and already
works. Do not scaffold a new project, and do not assume a blank slate.

Inspect the codebase first and establish:

- The existing application structure and where code of this kind already lives.
- The framework and version in use.
- The existing design system — colours, spacing, typography, and component conventions.
- Existing UI components you can reuse instead of writing new ones.
- The existing database structure, if this feature needs to persist anything.
- The existing authentication and authorization system, if this feature is user-scoped.
- Dependencies already installed, so you don't add a library that duplicates one.
- The existing test setup and conventions.

Only start writing code once you understand the above. If the application
already implements part of this feature, extend it rather than replacing it.

## Implementation Instructions

1. Generate links only on the server, from a record the requesting user is permitted to bill for. Price, currency, and quantity limits come from that record, never from the request.
2. Decide per link whether it is single-use or reusable, and enforce it in the app rather than assuming the shared URL will be treated politely. A link posted publicly will be opened by people you did not send it to.
3. Attach the app's own reference for the record so an incoming payment can be matched back without a human reading the description. Keep that reference opaque and free of names, emails, or anything else that should not travel with a public link.
4. Recognise payment through verified server-side confirmations. The browser returning from a link proves only that a browser returned.
5. Restrict who may create a link with a non-standard price, a discount, or a custom amount, and record who created each one. Without that, any user with access to the screen can quietly sell your product at whatever price they choose.

## UI and UX Requirements

Match the application's existing design system exactly. Reuse its components,
spacing, and typography. This feature should look like it was always there.

## Responsive Requirements

Works on mobile, tablet, and desktop. Touch targets are large enough to hit on a
phone, and nothing overflows horizontally at 320px.

## Accessibility Requirements

- Fully keyboard navigable.
- Correct semantic elements and ARIA roles.
- Visible focus states.
- Meets WCAG AA contrast.
- Dynamic changes are announced to screen readers.
- Respects prefers-reduced-motion.

## Edge Cases

- Reusable and single-use links behave very differently once shared. A single-use link opened a second time must show a clear expired state, and a reusable link must state whether quantity is fixed or chosen by the payer.
- Metadata travelling with a link is not private. Carry an internal identifier only, and resolve everything else server-side after payment.
- When the underlying offer changes price, is withdrawn, or its record is deleted, existing links must be deactivated rather than left selling something at the old terms.
- Payment confirmation must come from a verified server event, because payers frequently close the tab before being redirected back and the app would otherwise never learn they paid.
- Link creation must be permission-gated per price variation, and the creator recorded, so a discounted or custom-amount link can be traced to whoever issued it.
- The provider will resend confirmations. Match each one to the link and the payment it belongs to so a retry does not fulfil the same order twice.
- Give every link an expiry, even a long one, so an abandoned link does not stay live indefinitely after everyone has forgotten it.
- If the provider fails while a link is being created, do not leave a half-created record that shows a link the user cannot open.

## Testing

Exercise the feature end to end in the running application. Cover every edge case
above, then run the existing test suite and confirm nothing regressed.

## Acceptance Criteria

- [ ] Links are generated server-side with price and quantity taken only from the source record.
- [ ] Single-use links refuse a second payment and show an explicit expired state.
- [ ] Links carry an opaque internal reference and no personal or sensitive data.
- [ ] Changing or withdrawing the underlying offer deactivates its outstanding links.
- [ ] Fulfilment happens on a verified server confirmation and is idempotent across retries.
- [ ] Creating a discounted or custom-price link requires an explicit permission and is attributed to its creator.
- [ ] Every link has an expiry and the app shows its current status alongside the record.
- [ ] The feature matches the existing design system.
- [ ] No existing functionality is broken.

## Adaptation Rules

- Match the existing design system. Do not introduce a new colour palette,
  spacing scale, or component library.
- Reuse existing components and utilities wherever they fit.
- Follow the naming, file layout, and code style already present.
- Do not upgrade, replace, or remove existing dependencies to make this
  feature fit. Adapt the feature to the app, not the app to the feature.
- Do not break existing functionality. If a change is genuinely required in
  existing code, make the smallest one that works and say so.
- If something in these instructions conflicts with how the application is
  built, follow the application and explain the deviation.

## Final Verification

Before you report the work as done:

1. Re-read the acceptance criteria above and check each one against what you
   actually built.
2. Run the application and exercise the feature end to end.
3. Run the existing test suite and confirm you have broken nothing.
4. Check the feature on mobile, tablet, and desktop widths.
5. Check keyboard navigation and focus handling.
6. Summarize what changed: files added, files modified, and anything you
   deliberately did differently because of how this application is built.

If any acceptance criterion is unmet, fix it before reporting completion.