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)
+  })
+})