# Email Verification

## Objective

Confirm the user actually controls the address on the account.

A verification email with a single-use expiring link, a resend path, and defined behaviour for every way that link can be opened.

## 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. Issue single-use tokens with a stated expiry, stored hashed. A token you can read out of your own database is a token support can be tricked into using.
2. Decide what unverified accounts may do and enforce it on the server. Hiding features in the UI while the endpoints stay open verifies nothing.
3. When the user changes their email, verify the new address before it replaces the old one, and notify the old address that a change was requested.
4. Rate-limit resends per address and per account, but keep a path forward when delivery genuinely fails — a hard lockout after three bounces turns into a support ticket.
5. Never confirm or deny whether an address already belongs to an account in any response, including timing and error copy.

## 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

- Clicking an already-used link must show 'already verified', not an error.
- Clicking a link while signed out, or while signed in as a different user, must be handled explicitly rather than verifying the wrong account.
- Requesting a new link must invalidate the previous one, and the copy must say so — otherwise people click the older email.
- Email clients and security scanners pre-fetch links; a GET that consumes the token will be burned before the user sees it.
- An expired link must offer a one-click resend, not send the user back to the start.
- Changing the email again before the first change is confirmed must not leave two pending addresses.

## 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

- [ ] Verification tokens are single-use, expiring, and stored hashed.
- [ ] Restrictions on unverified accounts are enforced server-side.
- [ ] Already-verified, expired, and reused links each have their own clear state.
- [ ] Email changes verify the new address before it takes effect and notify the old one.
- [ ] Resends are rate-limited and always recoverable.
- [ ] No response reveals whether an address is registered.
- [ ] 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.