# Stale Data Indicator

## Objective

Tell people when the screen is out of date, and give them a safe way to refresh.

A visible marker of data age on cached or background-refreshed screens, with a manual refresh.

## 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. Find the screens serving cached or polled data and record when each was last successfully fetched.
2. Show the age only once it matters. A freshness label on data that is two seconds old is noise.
3. Distinguish three states clearly: cached and ageing, refresh failed, and offline. They call for different copy and different actions.
4. Give the user a manual refresh that re-runs the fetch for that view rather than reloading the page.
5. Do not silently replace what is on screen while the user is reading or editing it. Fetch, then offer the update.
6. Do not auto-refresh a background tab on a timer; refresh when it becomes visible again.

## 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

- A refresh must never discard unsaved local edits. Hold the new data until the form is clean or the user chooses.
- Repeated clicks on refresh must not spawn parallel requests; disable the control while one is in flight.
- Timestamps must render in the user's locale and time zone, not the server's.
- A failed refresh must keep showing the old data with a warning, not blank the view.
- Do not mark data stale purely because a websocket dropped, if the underlying record has not changed.
- A device with a badly wrong clock must not produce ages in the future.

## 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

- [ ] Cached screens show when the data was last fetched.
- [ ] Stale, failed, and offline are visually and textually distinct.
- [ ] Manual refresh re-fetches the view without a full page reload.
- [ ] Unsaved edits survive a refresh.
- [ ] Concurrent refresh requests are prevented.
- [ ] Timestamps respect the user's locale and time zone.
- [ ] 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.