# Countdown Timer

## Objective

A live countdown to a deadline that ends cleanly instead of running negative.

A countdown component driven by a server-provided deadline, with a defined finished state.

## 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. Send the deadline and the server's current time together, compute the offset between server and device once, and count against the corrected value. The device clock cannot be trusted to be right.
2. Recompute the remaining time from the corrected clock on every tick rather than decrementing a stored number, so a suspended tab does not resume showing a value minutes behind reality.
3. Define the finished state explicitly: what the component shows at zero, whether it reveals something, disables a control, or triggers a refetch. Reuse the app's existing Progress Indicator System styling rather than introducing new type and colour for the digits.
4. Reserve the widest layout the digits will ever occupy so the surrounding content does not shift as the count crosses from two digits to one, or drops the hours segment.
5. Do not treat the client countdown as enforcement. Whatever the deadline gates must be checked again on the server, because anyone can change their clock or edit the displayed value.

## 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 backgrounded or sleeping tab stops receiving ticks. On becoming visible again, recompute from the corrected clock and render the true remaining time rather than continuing from where the timer paused.
- The device clock may be wrong by hours or set deliberately. Anchor to a server timestamp delivered with the page and treat the device only as a source of elapsed time since that anchor.
- A countdown that reaches zero must switch to its finished state, not continue into negative numbers. Decide what happens at zero before building the counting.
- Announcing every second to a screen reader is unusable. Give the timer an accessible label with the remaining time and announce only at meaningful intervals, such as at the last few minutes and at zero.
- Stop the tick when the component is offscreen or the tab is hidden, and under prefers-reduced-motion render a static remaining time updated infrequently instead of a live ticking display.
- A deadline already in the past when the page loads must render finished immediately, with no flash of a large positive number.
- The unit labels and number formatting must follow the viewer's locale, and the largest unit should drop away as it empties rather than showing a leading zero for days.
- Multiple countdowns on one page should share a single tick rather than each running their own interval.

## 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

- [ ] The countdown is anchored to a server timestamp and is unaffected by a wrong device clock.
- [ ] Returning to a backgrounded tab shows the correct remaining time immediately.
- [ ] Reaching zero switches to a defined finished state and never displays negative time.
- [ ] A deadline already past renders finished on first paint with no flash.
- [ ] Ticking stops when the component is hidden and is suppressed under prefers-reduced-motion.
- [ ] Remaining time is available to screen readers without per-second announcements.
- [ ] The digits occupy reserved space and the layout does not shift as units change.
- [ ] 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.