# Address Autocomplete

## Objective

Help people enter an address fast without trapping them in a bad suggestion.

A suggestion-backed address field that fills structured components and always allows full manual entry.

## 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. Always keep manual entry available and obvious. Suggestion providers miss new builds, rural addresses, and much of the world; a form that only accepts a suggestion is a form some users cannot complete.
2. Store the structured components — line one, line two, locality, region, postal code, country — alongside the provider's formatted string and its place identifier. Storing only the formatted string makes the data unqueryable later.
3. Do not send keystrokes to the provider on the first character. Wait for meaningful input and debounce. Every request costs money and sends a user's partial address to a third party.
4. Let the user edit any field after a suggestion is applied, and keep their edits — do not overwrite corrections with provider data.
5. Adapt the field layout to the selected country. Fixed 'State' and 'ZIP' labels are wrong for most of the world, and required-postcode rules vary.
6. Never block submission on the provider. If it is slow, down, or over quota, the form must still accept a typed address.

## 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

- Apartment, unit, and suite numbers are frequently absent from suggestions — always provide a second line and preserve it.
- Selecting a suggestion by keyboard must work identically to clicking one.
- Addresses with no postal code, or postal codes with letters, must be accepted where valid.
- A user may change country after typing — reset provider bias and re-validate the fields rather than keeping stale ones.
- Provider terms often restrict storing or displaying their data; check before caching results.
- Announce the number of suggestions and the highlighted option to screen readers; a silent list is unusable.

## 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

- [ ] An address can be completed entirely by hand with no suggestion selected.
- [ ] Structured components and the original formatted string are both stored.
- [ ] No provider request is made before meaningful, debounced input.
- [ ] Manual corrections after selecting a suggestion are preserved.
- [ ] Field labels and required rules change with the selected country.
- [ ] A provider outage does not prevent form submission.
- [ ] The suggestion list is fully keyboard operable and announced.
- [ ] 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.