# Presence Indicators

## Objective

Show who else is on this screen right now.

Live avatars of the other users currently viewing or editing the same record.

## 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. Have each client heartbeat its presence on a short interval and treat presence as expiring state, not as a flag toggled on connect and off on disconnect.
2. Expire an entry after a couple of missed heartbeats. Crashed tabs, killed apps, and sleeping laptops never send a disconnect.
3. Collapse a user's multiple tabs and devices into one avatar. Three of the same face means the plumbing is leaking, not that three people are here.
4. Scope presence to the record and the workspace, and check the viewer's permission before revealing that someone is present.
5. Do NOT present presence as a lock. It tells the user someone else is here; it does not prevent a conflicting edit, and implying otherwise causes lost work.

## 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

- Tabs in the background should throttle or stop heartbeating, so an idle tab does not report an attentive user.
- Presence is a privacy surface. Some users and some plans must be able to browse without broadcasting it, and that setting must be honoured.
- When the realtime transport is down, hide the indicator entirely rather than showing a stale roster that says nobody is here.
- Cap the visible avatars and roll the rest into a count — a busy record can have dozens.
- Do not leak identity beyond what the viewer can already see; a name or avatar is still an information disclosure.
- Viewing and editing are different signals. If you show both, keep them visually distinct.

## 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

- [ ] Presence is heartbeat-driven and expires without an explicit disconnect.
- [ ] Ghost entries clear within seconds of a crashed or sleeping client.
- [ ] Multiple tabs and devices for one user render as a single avatar.
- [ ] Presence is scoped by record, workspace, and viewer permission.
- [ ] Users can opt out of broadcasting their presence.
- [ ] The indicator hides when realtime is unavailable rather than showing stale data.
- [ ] 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.