# Route Change Progress

## Objective

Show that a page change is underway when navigation isn't instant.

A single global indicator at the top of the app that appears while a client-side navigation is in flight.

## 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. Add one indicator, owned globally, tied to the app's navigation lifecycle rather than to any individual view.
2. Delay its appearance by roughly 200ms. Most navigations finish before that, and an indicator that flashes on every click reads as jank.
3. Complete or cancel it on every terminal outcome — success, redirect, error, and user-cancelled back navigation.
4. Do not use this to cover the arrival of data inside a view. Per-view content placeholders are owned by Skeleton Loading; extend that rather than building a second one. The two must never be visible at the same time — once the route has committed, this indicator is finished.
5. Announce only transitions that run long. A polite live-region message after a couple of seconds is enough; do not narrate every route change.

## 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 navigation that redirects must finish the indicator on the final destination, not the intermediate one.
- A failed navigation must clear the indicator and surface the error, never leave a bar stuck at 90%.
- Rapid successive navigations must reuse one indicator, not stack several.
- Browser back and forward are navigations too, and are often instant from cache — the delay threshold matters most here.
- The bar must sit above sticky headers and modals without covering a focused control.
- Respect prefers-reduced-motion: keep the state change, drop the animated crawl.

## 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

- [ ] Exactly one navigation indicator exists app-wide.
- [ ] Navigations faster than the delay threshold show nothing.
- [ ] Redirects, errors, and cancellations all clear the indicator.
- [ ] The indicator and any per-view skeleton are never on screen together.
- [ ] Long transitions are announced once to screen readers, short ones silently.
- [ ] The indicator never obscures content or a focused element.
- [ ] 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.