# Stepper Component

## Objective

Show people where they are in a multi-step flow and what is still ahead of them.

A single stepper used by every staged flow in the app, showing step order, completion, and errors.

## 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 every staged flow the app already has — onboarding, checkout, import wizards, multi-page settings — and render them all through one stepper rather than the three variants that have grown up separately.
2. Keep completion and navigation as two distinct concepts. A step can be complete without being current, and a step the user is allowed to jump back to is not the same as a step they have finished.
3. Model optional and skippable steps explicitly, and show a skipped step as skipped rather than as complete or as untouched. A user who skipped payment details needs to see that it is still outstanding.
4. Surface validation failures on the step that owns them, so a user standing on step four can see that step two is broken and reach it in one click.
5. Do not make the stepper the source of truth for flow state. It reads from whatever already drives the flow; if it holds its own copy the two will disagree the first time a step is added.

## 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

- Marking a step as reachable is not the same as marking it done — a stepper that lets the user click ahead to step five must not therefore paint steps three and four as complete.
- Optional steps need their own treatment, and a step the user deliberately skipped must remain visibly outstanding rather than quietly counting toward the finish.
- A step holding a validation error must say so on the step indicator itself, with the error state distinguishable from the current-step state and not conveyed by colour alone.
- On narrow screens a horizontal row of seven steps becomes unreadable — collapse to a compact form such as step three of seven with the current step's label, and keep the full list reachable.
- Steps added or removed mid-flow, for example a billing step that only appears on a paid plan, must renumber without stranding the user on a step that no longer exists.
- The current step must be announced to screen readers when it changes, and completed steps must carry their state in the accessible name, not in an icon with no text alternative.
- Returning to a flow from a link or a reload must restore the stepper to the persisted position rather than resetting to step one.

## 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

- [ ] Every staged flow in the app renders through the same stepper.
- [ ] Completion, current position, skipped, and error are four visually and textually distinct states.
- [ ] A step carrying a validation error is identifiable from any other step and navigable in one action.
- [ ] Narrow viewports show a compact stepper with no horizontal overflow.
- [ ] Step changes and step states are announced to assistive technology.
- [ ] Adding or removing a conditional step renumbers the flow without breaking the user's position.
- [ ] 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.