feat(F-072): completed feature

work/artifacts/F-072/architect.md

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+# F-072 — Architect: Dynamic VAT tax rates in product edit prices tab
+
+## Current state
+
+`PricingSection.tsx` (admin) has **hardcoded** VAT logic:
+```ts
+const VAT_GENERAL = 1.21;   // hardcoded constant
+const VAT_REDUCED = 1.10;    // hardcoded constant
+
+// calcGross: gross = net * VAT_GENERAL/VAT_REDUCED
+```
+
+The dropdown has **two hardcoded options**:
+```tsx
+<option value="general">21% gen.</option>
+<option value="reduced">10% red.</option>
+```
+
+But the DB `tax_rates` table already has **3 active rates**:
+- IVA Superreducido: 4% (applies_to: `super-reduced`)
+- IVA Reducido: 10% (applies_to: `reduced`)
+- IVA General: 21% (applies_to: `general`)
+
+The 4% rate is **missing** from the dropdown and calculation.
+
+## Goal
+
+Replace hardcoded VAT constants and dropdown with **dynamic** fetch of active tax rates from `GET /admin/tax-rates`. Also add `super-reduced` support to the backend so the 4% rate can be used.
+
+## Scope IN
+
+- `project/src/modules/pricing/domain/price.ts` — add `super-reduced` to `VatRate` type and `VAT_BASIS_POINTS`
+- `project/src/modules/pricing/api/pricing.routes.ts` — accept 'super-reduced' in `vatRateSchema`
+- `project/migrations/031_vat_super_reduced.js` — update CHECK constraints on `pricing_variant_prices.vat_rate` and `pricing_price_history` columns to include 'super-reduced'
+- `project/apps/admin/src/features/products/components/sections/PricingSection.tsx` — fetch active tax rates from `GET /admin/tax-rates`, populate dropdown dynamically, use fetched rate percentages for calculations
+- `project/apps/admin/src/lib/api-client.ts` — extend `VariantPrice.vatRate` type to include `super-reduced`
+
+## Scope OUT
+
+- Tax rates admin page (`/tax-rates`) — no changes needed, already supports activate/deactivate
+- Backend pricing service — already generic, only needs domain type update
+- Storefront/frontend — no changes
+
+## Design
+
+### Backend: add super-reduced
+
+`price.ts`:
+```ts
+export type VatRate = 'general' | 'reduced' | 'super-reduced';
+export const VAT_BASIS_POINTS: Record<VatRate, number> = {
+  general: 2100,      // 21%
+  reduced: 1000,      // 10%
+  'super-reduced': 400, // 4%
+};
+```
+
+`pricing.routes.ts` — `vatRateSchema`:
+```ts
+const vatRateSchema = z.enum(['general', 'reduced', 'super-reduced']);
+```
+
+### Migration 031
+
+Update CHECK constraints to:
+```sql
+CHECK (vat_rate IN ('general', 'reduced', 'super-reduced'))
+```
+
+### PricingSection.tsx
+
+1. Add `TaxRate[]` state for active tax rates
+2. `useEffect` on mount: fetch `taxApi.list()`, filter `active === true`
+3. Replace `VAT_GENERAL/VAT_REDUCED` constants with dynamic lookup:
+   ```ts
+   const rate = activeRates.find(r => r.appliesTo === vatRate[variantId]);
+   const multiplier = 1 + (rate?.ratePercent ?? 21) / 100;
+   const grossCents = Math.round(netCents * multiplier);
+   ```
+4. Dropdown maps `appliesTo` → option value, displays `name + ratePercent%`:
+   ```tsx
+   {activeRates.map(r => (
+     <option key={r.appliesTo} value={r.appliesTo}>
+       {r.name} ({r.ratePercent}%)
+     </option>
+   ))}
+   ```
+5. `setVatRate` stores `appliesTo` key (e.g. `'super-reduced'`) as the vat rate value
+6. Default: use first active rate if none selected
+
+### Admin api-client
+
+Extend `VariantPrice.vatRate` type to include `'super-reduced'`:
+```ts
+vatRate: 'general' | 'reduced' | 'super-reduced';
+```
+
+## Risk
+
+- **Low risk**: adding a new allowed value to an existing enum + updating a CHECK constraint; no data migration needed (existing data already uses 'general' or 'reduced')
+- **Risk mitigation**: migration is additive (adds 'super-reduced' to allowed values, doesn't remove any); rollback simply reverts constraint
+
+## Verification
+
+- `npx tsc --noEmit` on all projects
+- `npx eslint` on changed files
+- Apply migration 031 to dev DB
+- Backend rebuilt and restarted
+- API test: `PATCH /pricing/variants/:id` with `vatRate: 'super-reduced'` → HTTP 200
+- Admin product edit → pricing tab → dropdown shows all 3 active rates
+- `./scripts/verify.sh` green