fix(supplier-invoices): reverse credit notes on paid kontantmetoden invoices (#1430)

Under kontantmetoden the credit flow skipped the reversing verifikat
entirely, gated on accounting_method === 'accrual' in all three surfaces
(dashboard route, v1 route, pending-operations commit).

That is right only while the original is still UNPAID: nothing reached the
ledger, so there is no entry to reverse and recognition waits for cash. But
a PAID original was already booked by its payment verifikat (expense +
2641 ingaende moms). Crediting it marked the invoice 'credited' with zero
accounting trace, leaving both the cost and the moms deduction overstated
and nothing to link a later refund back to.

Adds supplierCreditNoteNeedsJournalEntry(), the mirror of the customer
side's creditNoteNeedsJournalEntry(): reverse whenever the original
actually reached the ledger, whatever the configured method.
createSupplierCreditNoteEntry's existing shape already suits the cash case,
the 2440 debit leaves a claim on the supplier that the refund clears, just
as the customer side leaves a 1510 credit for a refund owed.

The v1 route's GDPR-minimised projection dropped exactly the booked-ness
columns this needs; they are restored with a comment explaining why, since
status alone misses a part-paid-but-booked original (rows predating #1413).

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

lib/bookkeeping/__tests__/booking-mode.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest'
-import { booksInvoicesOnIssue, cashPartialBlockReason } from '../booking-mode'
+import { booksInvoicesOnIssue, cashPartialBlockReason, supplierCreditNoteNeedsJournalEntry } from '../booking-mode'
 
 describe('booksInvoicesOnIssue (#967)', () => {
   it('books at issue for accrual companies by default', () => {
@@ -66,3 +66,69 @@ describe('cashPartialBlockReason', () => {
     expect(cashPartialBlockReason({ ...base, priorPaidAmount: undefined })).toBeNull()
   })
 })
+
+describe('supplierCreditNoteNeedsJournalEntry', () => {
+  const unpaid = {
+    registration_journal_entry_id: null,
+    payment_journal_entry_id: null,
+    status: 'registered',
+    paid_at: null,
+    paid_amount: 0,
+  }
+
+  it('always reverses under faktureringsmetoden, even for an unpaid original', () => {
+    expect(supplierCreditNoteNeedsJournalEntry('accrual', unpaid)).toBe(true)
+    // Empty/absent accounting_method falls back to accrual, matching the rest
+    // of the module.
+    expect(supplierCreditNoteNeedsJournalEntry('', unpaid)).toBe(true)
+  })
+
+  it('skips under kontantmetoden while the original is still unpaid', () => {
+    // Nothing reached the ledger: there is no entry to reverse and
+    // recognition correctly waits for the refund.
+    expect(supplierCreditNoteNeedsJournalEntry('cash', unpaid)).toBe(false)
+  })
+
+  it('reverses under kontantmetoden once the payment booked the expense', () => {
+    // The payment verifikat already booked expense + 2641 ingående moms;
+    // skipping the reversal would overstate both.
+    expect(
+      supplierCreditNoteNeedsJournalEntry('cash', {
+        ...unpaid,
+        status: 'paid',
+        paid_at: '2026-03-12',
+        paid_amount: 781,
+        payment_journal_entry_id: 'je-1',
+      }),
+    ).toBe(true)
+  })
+
+  it('reverses on any single booked-ness signal in isolation', () => {
+    // Each signal must stand alone: rows written by different payment paths
+    // set different subsets of these fields.
+    expect(supplierCreditNoteNeedsJournalEntry('cash', { ...unpaid, payment_journal_entry_id: 'je-1' })).toBe(true)
+    expect(supplierCreditNoteNeedsJournalEntry('cash', { ...unpaid, registration_journal_entry_id: 'je-2' })).toBe(true)
+    expect(supplierCreditNoteNeedsJournalEntry('cash', { ...unpaid, status: 'paid' })).toBe(true)
+    expect(supplierCreditNoteNeedsJournalEntry('cash', { ...unpaid, paid_at: '2026-03-12' })).toBe(true)
+  })
+
+  it('catches a part-paid original that predates the #1413 guard', () => {
+    // status is still 'partially_paid', but a payment entry exists, so the
+    // expense IS on the ledger. status alone would miss this.
+    expect(
+      supplierCreditNoteNeedsJournalEntry('cash', {
+        ...unpaid,
+        status: 'partially_paid',
+        paid_amount: 781,
+        payment_journal_entry_id: 'je-3',
+      }),
+    ).toBe(true)
+  })
+
+  it('ignores sub-öre noise and missing rows', () => {
+    expect(supplierCreditNoteNeedsJournalEntry('cash', { ...unpaid, paid_amount: 0.004 })).toBe(false)
+    expect(supplierCreditNoteNeedsJournalEntry('cash', { ...unpaid, paid_amount: null })).toBe(false)
+    expect(supplierCreditNoteNeedsJournalEntry('cash', null)).toBe(false)
+    expect(supplierCreditNoteNeedsJournalEntry('cash', undefined)).toBe(false)
+  })
+})

lib/bookkeeping/booking-mode.ts

@@ -55,3 +55,50 @@ export function cashPartialBlockReason(opts: {
   if (Math.round((opts.priorPaidAmount ?? 0) * 100) !== 0) return 'previously_partially_paid'
   return null
 }
+
+/** The booked-ness signals on a supplier invoice being credited. */
+export interface SupplierCreditNoteOriginal {
+  /** Set when the invoice was booked at registration (faktureringsmetoden). */
+  registration_journal_entry_id?: string | null
+  /** Set when the invoice was booked at payment (kontantmetoden). */
+  payment_journal_entry_id?: string | null
+  status?: string | null
+  paid_at?: string | null
+  paid_amount?: number | null
+}
+
+/**
+ * Whether a supplier credit note must post a reversing verifikat.
+ *
+ * The mirror of creditNoteNeedsJournalEntry() on the customer side: a credit
+ * note reverses whatever actually reached the ledger, so the test is "did the
+ * original get booked", not "which accounting method is configured".
+ *
+ * Under faktureringsmetoden the original was booked at registration, so the
+ * reversal always applies. Under kontantmetoden nothing is booked at
+ * registration, and skipping the credit note is correct while the invoice is
+ * still unpaid: there is no entry to reverse and recognition waits for cash.
+ * But once the invoice has been PAID, the payment verifikat has already booked
+ * the expense and claimed the ingående moms (2641, ruta 48). Leaving that
+ * un-reversed overstates both the cost and the VAT deduction for as long as
+ * the credit stands, and the invoice is marked 'credited' with no accounting
+ * trace at all, so nothing links a later refund back to it.
+ *
+ * createSupplierCreditNoteEntry's shape works for both cases: the 2440 debit
+ * leaves a claim on the supplier that the refund payment clears, exactly as
+ * the customer side leaves a 1510 credit for a refund owed to the customer.
+ */
+export function supplierCreditNoteNeedsJournalEntry(
+  accountingMethod: string,
+  original: SupplierCreditNoteOriginal | null | undefined,
+): boolean {
+  if ((accountingMethod || 'accrual') === 'accrual') return true
+  if (!original) return false
+  return (
+    !!original.registration_journal_entry_id ||
+    !!original.payment_journal_entry_id ||
+    original.status === 'paid' ||
+    !!original.paid_at ||
+    Math.round(Math.abs(original.paid_amount ?? 0) * 100) !== 0
+  )
+}

lib/pending-operations/commit.ts

@@ -35,7 +35,7 @@ import {
   createCreditNoteJournalEntry,
 } from '@/lib/bookkeeping/invoice-entries'
 import { resolveSettlementAccount } from '@/lib/bookkeeping/settlement-account'
-import { cashPartialBlockReason } from '@/lib/bookkeeping/booking-mode'
+import { cashPartialBlockReason, supplierCreditNoteNeedsJournalEntry } from '@/lib/bookkeeping/booking-mode'
 import { ensureManualCashAccount } from '@/lib/cash-accounts/service'
 import { createJournalEntry, findFiscalPeriod, getSwedishLocalDate, reverseEntry, validateBalance } from '@/lib/bookkeeping/engine'
 import {
@@ -3787,7 +3787,10 @@ async function commitCreditSupplierInvoice(
   const accountingMethod = settings?.accounting_method || 'accrual'
 
   let journalEntryId: string | null = null
-  if (accountingMethod === 'accrual') {
+  // Kontantmetoden skips only while the original is still UNPAID: a paid one
+  // was already booked by its payment verifikat (expense + 2641 ingående
+  // moms), and leaving that un-reversed overstates cost and moms deduction.
+  if (supplierCreditNoteNeedsJournalEntry(accountingMethod, original)) {
     try {
       const je = await createSupplierCreditNoteEntry(
         supabase,