fix(bookkeeping): gnubok_categorize_transaction now handles incoming expense refunds correctly (#761)

Incoming expense refunds (positive amount on an expense category) previously
booked with inverted debit/credit — crediting the bank and debiting the expense
account — which both imbalanced the book and reported negative bank flow.

getCategoryAccountMapping now detects amount > 0 on expense categories and
returns the reversed mapping: debit 1930, credit expense account, with 2641
as vatCreditAccount so ingående moms is correctly reversed on the VAT line.
The VAT line description is "Återföring ingående moms X%" rather than the
income-side "Utgående moms" label.

Signed-off-by: Jonas Flodén <jonas@floden.nu>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/bookkeeping/__tests__/category-mapping.test.ts

@@ -381,6 +381,64 @@ describe('private transaction accounts by entity type and direction', () => {
   })
 })
 
+describe('incoming expense refund (positive amount, expense category)', () => {
+  it('getCategoryAccountMapping swaps accounts: bank debited, expense account credited', () => {
+    const result = getCategoryAccountMapping('expense_software', 500, true)
+    expect(result.debitAccount).toBe('1930')
+    expect(result.creditAccount).toBe('5420')
+  })
+
+  it('getCategoryAccountMapping sets vatCreditAccount 2641 and clears vatDebitAccount for refund', () => {
+    const result = getCategoryAccountMapping('expense_software', 500, true)
+    expect(result.vatDebitAccount).toBeNull()
+    expect(result.vatCreditAccount).toBe('2641')
+  })
+
+  it('VAT-exempt expense refund (bank_fees) has no VAT accounts', () => {
+    const result = getCategoryAccountMapping('expense_bank_fees', 100, true)
+    expect(result.debitAccount).toBe('1930')
+    expect(result.creditAccount).toBe('6570')
+    expect(result.vatDebitAccount).toBeNull()
+    expect(result.vatCreditAccount).toBeNull()
+  })
+
+  it('buildMappingResultFromCategory generates credit line on 2641 for expense refund', () => {
+    const tx = makeTransaction({ amount: 1000 })
+    const result = buildMappingResultFromCategory('expense_software', tx, true)
+    expect(result.vat_lines).toHaveLength(1)
+    expect(result.vat_lines[0].account_number).toBe('2641')
+    expect(result.vat_lines[0].credit_amount).toBe(200)
+    expect(result.vat_lines[0].debit_amount).toBe(0)
+  })
+
+  it('buildMappingResultFromCategory uses återföring description for expense refund VAT', () => {
+    const tx = makeTransaction({ amount: 1000 })
+    const result = buildMappingResultFromCategory('expense_software', tx, true)
+    expect(result.vat_lines[0].description).toBe('Återföring ingående moms 25%')
+  })
+
+  it('buildMappingResultFromCategory generates no VAT line for VAT-exempt expense refund', () => {
+    const tx = makeTransaction({ amount: 100 })
+    const result = buildMappingResultFromCategory('expense_bank_fees', tx, true)
+    expect(result.vat_lines).toHaveLength(0)
+  })
+
+  it('buildMappingResultFromCategory maps debit/credit correctly (bank debited, expense credited)', () => {
+    const tx = makeTransaction({ amount: 1250 })
+    const result = buildMappingResultFromCategory('expense_software', tx, true)
+    expect(result.debit_account).toBe('1930')
+    expect(result.credit_account).toBe('5420')
+  })
+
+  it('vat_amount override on expense refund uses återföring description', () => {
+    const tx = makeTransaction({ amount: 1250 })
+    const result = buildMappingResultFromCategory('expense_software', tx, true, 'enskild_firma', 'standard_25', 200)
+    expect(result.vat_lines).toHaveLength(1)
+    expect(result.vat_lines[0].credit_amount).toBe(200)
+    expect(result.vat_lines[0].description).toBe('Återföring ingående moms (enligt underlag)')
+  })
+})
+
 describe('category default → leaf account guarantee', () => {
   // BAS encodes the parent/leaf distinction in account_name via the
   // "(gruppkonto)" suffix. Auditors and Skatteverket downstream reporting

lib/bookkeeping/category-mapping.ts

@@ -141,6 +141,18 @@ export function getCategoryAccountMapping(
     // Note: income tax deduction was abolished 2017 (IL 16 kap 2 §), but VAT deduction remains.
     const resolvedVat = vatTreatment ?? (isVatExempt ? null : category === 'expense_representation' ? 'reduced_12' : 'standard_25')
 
+    if (amount > 0) {
+      // Incoming refund: bank receives money, expense account is reduced (credited).
+      // Ingående moms is reversed — credit 2641 instead of debit.
+      return {
+        debitAccount: BANK_ACCOUNT,
+        creditAccount: expenseAccount,
+        vatTreatment: resolvedVat,
+        vatDebitAccount: null,
+        vatCreditAccount: resolvedVat ? '2641' : null,
+      }
+    }
+
     return {
       debitAccount: expenseAccount,
       creditAccount: BANK_ACCOUNT,
@@ -291,12 +303,16 @@ export function buildMappingResultFromCategory(
           description: hasVatOverride ? 'Ingående moms (enligt underlag)' : `Ingående moms ${vatRate * 100}%`,
         })
       } else if (vatAmount > 0 && transaction.amount > 0 && mapping.vatCreditAccount) {
-        // Income: Utgående moms (output VAT)
+        // Income output VAT, or expense refund reversing ingående moms (both credit vatCreditAccount).
+        // Distinguish by account: 2641 = reversed ingående moms, 2611/2621/2631 = utgående moms.
+        const isExpenseRefund = mapping.vatCreditAccount === '2641'
         vatLines.push({
           account_number: mapping.vatCreditAccount,
           debit_amount: 0,
           credit_amount: vatAmount,
-          description: hasVatOverride ? 'Utgående moms (enligt underlag)' : `Utgående moms ${vatRate * 100}%`,
+          description: isExpenseRefund
+            ? (hasVatOverride ? 'Återföring ingående moms (enligt underlag)' : `Återföring ingående moms ${vatRate * 100}%`)
+            : (hasVatOverride ? 'Utgående moms (enligt underlag)' : `Utgående moms ${vatRate * 100}%`),
         })
       }
     }