# Reschedule and Cancel Links

## Objective

Give every booking confirmation a link the person can use to move or cancel it.

Tokenised self-service links in booking confirmations and reminders that let the attendee change or cancel without signing in.

## 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. Put the two links in the booking confirmation, in every reminder, and on the confirmation screen itself. A person looking for the link is usually looking in the last message they received.
2. Land the link on a page that restates the booking in plain terms before offering any action, so someone who opened it by accident can see what they are about to change and back out.
3. Reuse the app's existing Signed Share Links mechanism for token generation, expiry, and revocation rather than inventing a second token scheme. If the app has Magic Link Sign-In, note that this link grants access to one booking only and must never establish a full session.
4. Give the owner a configurable cutoff, expressed as a period before the start time, after which the links explain that changes must go through the host instead of failing with an error.
5. Do not build the link from the booking's own identifier or a sequential value. A guessable link lets anyone walk the range and cancel other people's bookings.

## 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

- Once the booking has started or passed, the link must stop working and say why. A link that still cancels a finished appointment corrupts the record and the reporting built on it.
- Inside the cutoff window the links must explain that self-service changes have closed and offer a way to contact the host, rather than presenting controls that then fail on submit.
- Tokens must be long, random, and unguessable, and stored so they cannot be read back from a database dump in usable form. Sequential or derived tokens let anyone enumerate and cancel other bookings.
- A slot chosen for a reschedule can be taken by someone else between the page loading and the confirmation. Re-check availability at the moment of commit and return the user to the picker with the slot marked gone rather than double-booking it.
- Both the attendee and the host are notified once per change. A retried delivery or a double submit must not send two cancellation notices for the same event.
- Cancelling must release the slot back to availability, and should trigger the Cancellation Waitlist if one exists, in the same transaction as the cancellation.
- A link that has already been used to cancel must show the cancelled state, not a fresh reschedule form.
- Reminders sent after a reschedule must carry the new time and a link that still works, not the payload frozen at booking time.

## 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

- [ ] Confirmations and reminders both carry working reschedule and cancel links.
- [ ] Links use unguessable tokens issued through the app's existing signed-link mechanism.
- [ ] The link grants access to one booking and never creates a signed-in session.
- [ ] Links expire after the booking passes and respect a configurable change cutoff with an explanatory message.
- [ ] A reschedule into a slot taken mid-flow fails safely and returns the user to the picker.
- [ ] Each change notifies both sides exactly once, and cancellation releases the slot.
- [ ] 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.