# Session Timeout Warning

## Objective

Warn people before an idle session expires, instead of losing their work.

A countdown dialog that appears before an idle session ends, with an explicit way to stay signed in.

## 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. Track genuine user activity — clicks, keystrokes, navigation — and show a warning dialog a meaningful interval before the session would expire.
2. Show a live countdown and a button that extends the session by making a real request to the server, not by resetting a local timer.
3. Synchronise the timer and the eventual sign-out across every open tab, so extending in one tab clears the warning in all of them.
4. On expiry, preserve the state of any open form and offer to restore it after the user signs back in.
5. Do NOT count background polling, autosave, or websocket traffic as user activity. That is how a session stays alive on an unattended machine, which is the exact thing the timeout exists to prevent.

## 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

- The server can expire the session before the local countdown finishes — clock skew and restarts both cause it. Handle a 401 arriving early without showing a stale countdown.
- A user who returns after the laptop slept must see the expired state, not a countdown resumed from where it paused.
- If policy requires explicit reauthentication, extending must prompt for a password rather than silently renewing.
- The warning must not steal focus from an input mid-typing, and Escape must not be the thing that lets the session lapse.
- Announce the countdown to screen readers once, not on every tick.
- Sign-out must clear the restored-work buffer on a shared machine.

## 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

- [ ] A countdown warning appears before an idle session expires.
- [ ] Extending the session performs a real server round-trip.
- [ ] The warning and the sign-out are synchronised across tabs.
- [ ] Background requests do not extend the session.
- [ ] Unsaved form state is preserved and offered back after reauthentication.
- [ ] Early server-side expiry is handled without a stale countdown.
- [ ] 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.