# Signed Share Links

## Objective

Share one private item with someone outside the app, without giving them an account.

Signed capability URLs scoped to a single record and a fixed set of actions, with expiry and revocation.

## 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 as unguessable signed tokens stored server-side, so a link can be revoked without rotating a global secret.
2. Scope each token to one record and an explicit action set — view, comment, download — and check that scope on every request the link serves.
3. Require an expiry at creation with a sane default, and give the owner a list of live links showing what each grants, when it was made, and when it was last opened.
4. Treat anyone holding the link as the intended recipient. That is the security model; state it in the sharing UI so the owner understands what forwarding means.
5. Do NOT put the token in a query string that leaks through referrers, server logs, or analytics, and do NOT let a link-holder discover other records by changing an ID in the path.

## 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

- An expired or revoked link must show the same neutral page whether or not the record ever existed — leaking that difference is an enumeration hole.
- Link previews from chat apps and mail clients will fetch the URL. Suppress metadata and thumbnails that expose contents to anyone who never opened it.
- Search engines must never index these pages; set noindex and exclude them from sitemaps.
- Deleting the underlying record must invalidate its links rather than serving a stale cached copy.
- Downgrading a link's scope has to take effect immediately for someone who already has the page open.
- Revoking the owner's own access, or deactivating their account, must revoke the links they issued.

## 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 unguessable, signed, stored server-side, and individually revocable.
- [ ] Each link is scoped to one record and one action set, enforced on every request.
- [ ] Every link has an expiry, and expired or revoked links show an identical neutral state.
- [ ] Owners can list, inspect, and revoke their live links.
- [ ] Tokens do not appear in referrers, logs, or analytics.
- [ ] Shared pages are excluded from search indexing and rich previews.
- [ ] 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.