Wayfinder: chart the Shopify headless commerce map

The route from "mozimo.in displays Shopify products" to "mozimo.in sells them",
as a plan with a phase spine and gates, plus the open decision tickets that
still shape it and the evidence they rest on.

- .scratch/shopify-headless-commerce/: plan.md (phases and gates), map.md (the
  wayfinder map), 10 open decision tickets
- CONTEXT.md: Storefront / Theme store / Cart / Parity vocabulary
- docs/adr/0001-0003: Checkout stays Shopify-hosted, one Variant per product,
  the checkout domain stays shop.mozimo.in
- docs/research/ and docs/shopify-catalog-inventory.md: verified store facts,
  the Cart API probe, and the catalogue inventory

Raw Shopify doc scrapes under .scratch/shopify-research/ are ignored: they are
working material, not record.

.scratch/shopify-headless-commerce/issues/10-confirm-customer-accounts-version.md

@@ -0,0 +1,23 @@
+# Confirm the customer accounts version
+
+`Type:` task
+`Status:` open
+
+Part of [the map](../map.md).
+
+## Question
+
+Is this store on new customer accounts or legacy (classic) customer accounts?
+
+Everything points to **new**: the admin panel exposes **Self-serve returns** and **Store credit** (✔ for new accounts, ✘ for legacy in Shopify's own comparison table), and the account URL is the `shopify.com/<id>/account` form that only the new system uses.
+
+But that URL is **not conclusive**. Shopify's upgrade guide populates the new URL *before* cutover, so a store mid-migration can show it while still serving legacy account pages. Legacy accounts were deprecated on 2026-02-26 and the **sunset date is still unannounced** as of October 2026 — so if this store is genuinely still on legacy, Phase 4 stops being a comfortable late phase and has to move ahead of the sunset.
+
+There are two clean discriminators, either of which settles it:
+
+- The **Upgrade banner** on Settings → Customer accounts.
+- Admin GraphQL `Shop.customerAccountsV2.customerAccountsVersion`, which returns `CLASSIC` or `NEW_CUSTOMER_ACCOUNTS`.
+
+## Answer
+
+<!-- filled on resolution -->