feat(vat): add per-account declaration treatments (#1588)

Closes #1457

supabase/migrations/20260813124930_add_account_default_vat_treatment.sql

@@ -0,0 +1,19 @@
+ALTER TABLE public.chart_of_accounts
+  ADD COLUMN IF NOT EXISTS default_vat_treatment text;
+
+ALTER TABLE public.chart_of_accounts
+  DROP CONSTRAINT IF EXISTS chart_of_accounts_default_vat_treatment_check;
+
+ALTER TABLE public.chart_of_accounts
+  ADD CONSTRAINT chart_of_accounts_default_vat_treatment_check
+  CHECK (default_vat_treatment IS NULL OR default_vat_treatment IN (
+    'standard_25', 'reduced_12', 'reduced_6', 'exempt',
+    'reverse_charge_domestic', 'reverse_charge_eu_goods',
+    'reverse_charge_eu_services', 'export_goods', 'export_services',
+    'vmb', 'rental_voluntary'
+  ));
+
+COMMENT ON COLUMN public.chart_of_accounts.default_vat_treatment IS
+  'Per-account momsdeklaration treatment. Explicit values override the built-in BAS account mapping.';
+
+NOTIFY pgrst, 'reload schema';

supabase/migrations/__tests__/account-default-vat-treatment.pg.test.ts

@@ -0,0 +1,47 @@
+import { describe, expect, it } from 'vitest'
+import { seedCompany } from '@/tests/pg/fixtures'
+import { getPool } from '@/tests/pg/setup'
+
+async function setTreatment(companyId: string, treatment: string | null) {
+  return getPool().query(
+    `UPDATE public.chart_of_accounts
+     SET default_vat_treatment = $2
+     WHERE company_id = $1 AND account_number = '3013'`,
+    [companyId, treatment],
+  )
+}
+
+async function insertAccount(companyId: string, userId: string) {
+  return getPool().query(
+    `INSERT INTO public.chart_of_accounts
+       (user_id, company_id, account_number, account_name, account_class,
+        account_group, account_type, normal_balance, plan_type,
+        is_system_account)
+     VALUES ($1, $2, '3013', 'Test account', 3, '30', 'revenue', 'credit',
+       'full_bas', false)
+     RETURNING account_number`,
+    [userId, companyId],
+  )
+}
+
+describe('chart_of_accounts.default_vat_treatment', () => {
+  it('accepts every supported treatment and NULL', async () => {
+    const { companyId, userId } = await seedCompany()
+    expect((await insertAccount(companyId, userId)).rowCount).toBe(1)
+    const treatments = [
+      'standard_25', 'reduced_12', 'reduced_6', 'exempt',
+      'reverse_charge_domestic', 'reverse_charge_eu_goods',
+      'reverse_charge_eu_services', 'export_goods', 'export_services',
+      'vmb', 'rental_voluntary', null,
+    ]
+    for (const treatment of treatments) {
+      await expect(setTreatment(companyId, treatment)).resolves.toMatchObject({ rowCount: 1 })
+    }
+  })
+
+  it('rejects unknown treatments', async () => {
+    const { companyId, userId } = await seedCompany()
+    expect((await insertAccount(companyId, userId)).rowCount).toBe(1)
+    await expect(setTreatment(companyId, 'unknown')).rejects.toThrow()
+  })
+})