# Unsaved Changes Guard

## Objective

Stop people navigating away from work they have not saved.

A warning on any attempt to leave a form with genuine unsaved changes, covering routing and browser navigation.

## 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. Compare the current form values against the values it loaded with. Track real changes, not merely whether a field was focused.
2. Cover all four exits: internal navigation, the back button, a page reload, and closing the tab.
3. Name what is at risk in the warning and offer to save rather than only to discard.
4. Clear the guard immediately on a successful save, an autosave, or an explicit reset.
5. Do not warn on a form the user never meaningfully touched. A guard that fires on an accidental keystroke gets dismissed on reflex, including the time it mattered.

## 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 field typed into and then changed back is not a change. Compare values, not events.
- A failed save must leave the guard in place and the data intact, not trap the user with no way out.
- A save still in flight should block navigation with a pending state, not a scary dialog.
- The browser's own beforeunload prompt cannot be styled or given custom text. Do not try; use it only for reload and tab close.
- Deliberate sign-out and session expiry must not fight the guard.
- Multi-step forms must guard the whole flow, not each step in isolation.

## 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

- [ ] Leaving a dirty form warns on internal navigation, back, reload, and tab close.
- [ ] An untouched form, or one edited back to its original values, never warns.
- [ ] A successful save or reset clears the guard immediately.
- [ ] The warning offers to save, not only to discard.
- [ ] A failed save leaves the user on the form with their 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.