# Browser Push Notifications

## Objective

Reach users with timely updates when the app is not open.

Web push subscriptions per device, with permission handled carefully and dead subscriptions cleaned up.

## 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. Register a service worker and store each push subscription against the user, with the device it came from and when it was last used.
2. Ask for permission only after a user action that implies they want it — enabling push in settings, or opting in on a record. Never on page load.
3. Show your own explanation before triggering the browser prompt, and let the user decline yours without burning the browser permission, which they cannot easily undo.
4. Deep-link each notification to the relevant record and re-check authorization when it opens; the notification may be hours old.
5. Do NOT put private content in the notification body. It renders on a locked screen anyone can see.

## 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

- Denied, dismissed, revoked, and unsupported are four different states and need four different UI outcomes.
- A subscription rejected by the push provider is dead — delete it rather than retrying it forever.
- A user with three devices should get one notification per device, and opening it on one should not leave it unread on the others.
- If the app is already open and focused on the relevant record, suppress the push and update in place.
- Push preferences must live on the existing notification preference model as another channel, not as an isolated toggle.
- Signing out on a device must remove that device's subscription, or the next user of that machine receives someone else's notifications.

## 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

- [ ] Permission is requested only after an explicit user action, behind an in-app explanation.
- [ ] Subscriptions are stored per device and removed on sign-out.
- [ ] Denied, revoked, and unsupported states each have their own handling.
- [ ] Provider-rejected subscriptions are deleted automatically.
- [ ] Notifications deep-link and re-check authorization on open.
- [ ] Push is a channel on the existing preference model.
- [ ] 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.