# Shopify Customer Sync

## Objective

Keep Shopify customers current from app users without crossing stores or resetting consent.

A sync that creates or updates a customer record in the connected store whenever an app user's details or consent change.

## 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 the app events that should reach the store — account creation, profile edit, address change, consent change — and sync from those events rather than sweeping every user on a timer.
2. Scope every request, every lookup, and every stored identifier to one connected shop. Treat the shop as part of the customer's identity, not as ambient configuration.
3. Store the provider's customer identifier against the app user per shop and match on it first, falling back to a normalized email address only when no identifier has been recorded yet.
4. Treat marketing consent as something the app records, not something it decides. Carry the consent the app actually captured, with its timestamp and source, and never mark a customer subscribed because they created an account.
5. Orders, line items, and fulfilment state are owned by Shopify Order Import; this brief owns the user-to-customer record only. Do not create or modify orders here, and do not write consent from an order payload.

## 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 workspace connected to more than one store must never resolve a customer by searching across all of them. A lookup scoped to the wrong shop returns another merchant's customer and writes app data into their store.
- Email marketing consent and SMS marketing consent are separate states with separate legal basis. Granting one because the user accepted the other is a compliance failure, not a convenience.
- The store merges duplicate customers and staff delete them. A stored identifier that now points at a merged or removed record must be re-resolved rather than retried forever as a failure.
- Guest checkout produces customers with no account behind them. Do not assume every customer in the store has a matching app user, and do not create app accounts to close the gap.
- If the store also sends customer updates back into the app, each side must ignore the changes it caused itself. Stamp the origin of every write and drop the echo, or one edit will bounce between the two systems indefinitely.
- A user changing their email address must update the existing customer rather than create a second one under the new address.
- The app must not push a blank value over a field a merchant filled in by hand. Send only the fields the app genuinely owns.
- When a store is disconnected or its credentials are revoked, queued syncs must be discarded rather than retried against an account the workspace no longer controls.

## 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 request and stored identifier is scoped to a single shop, and a multi-store workspace cannot read across them.
- [ ] Email and SMS marketing consent are stored and transmitted independently, each with its captured timestamp and source.
- [ ] A user with a stored customer identifier updates that customer; a user without one is matched by normalized email before any record is created.
- [ ] Merged, deleted, and guest customers each resolve to a defined outcome rather than a repeating failure.
- [ ] Bidirectional updates settle after one pass, with no echo loop between the app and the store.
- [ ] Disconnecting a store stops all pending and future syncs for it.
- [ ] 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.