fix(invoices): reminder emails use the per-currency payment account, never the SEK IBAN (#1806)

* fix(invoices): reminder emails use the per-currency payment account, never the SEK IBAN

Invoice PDF and invoice email resolve payment details by invoice currency
(invoice_payment_accounts, #1116), but the overdue-reminder templates still
read the legacy company_settings fields, so a EUR reminder printed the SEK
account's IBAN. A customer has paid to the wrong account from one.

Both reminder generators now go through companyWithInvoicePaymentAccount,
and sendReminder applies the same gate as invoice send: no usable account
for the invoice currency means the reminder is skipped with
INVOICE_PAYMENT_ACCOUNT_MISSING:<currency> in the result, instead of going
out with no (or the wrong) payment details.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(invoices): run the reminder payment-account gate before the fee entry and reminder row

Skeptic refutation (3/3): the gate lived in sendReminder, after
processOverdueReminders had already posted the 60 kr påminnelseavgift
verifikat and inserted the invoice_reminders row, so a skipped EUR reminder
booked a fee for an email never sent and burned the level for good. The
gate now runs in the loop before any write; sendReminder keeps it only as
a backstop for direct callers. New processor test asserts no fee entry, no
row and no email for the skipped case, and all three once an account exists.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

lib/invoices/reminder-processor.ts

@@ -10,6 +10,10 @@ import {
   type ReminderDaysConfig,
 } from '@/lib/email/reminder-templates'
 import { calculateLatePaymentInterest } from '@/lib/invoices/late-payment-interest'
+import {
+  hasUsableInvoicePaymentAccount,
+  resolveInvoicePaymentAccount,
+} from '@/lib/invoices/payment-accounts'
 import { createReminderFeeEntry } from '@/lib/bookkeeping/reminder-fee-entries'
 import { createLogger } from '@/lib/logger'
 import type { Invoice, Customer, CompanySettings } from '@/types'
@@ -119,6 +123,20 @@ export async function sendReminder(
     return { success: false, error: 'Customer has no email' }
   }
 
+  // Backstop for direct callers: processOverdueReminders applies this same
+  // gate BEFORE booking the fee and inserting the reminder row. A reminder
+  // with no payment account for the invoice currency would print nothing to
+  // pay to, or (before this gate) the SEK account's IBAN on a EUR invoice.
+  const currency = invoice.currency
+  if (!hasUsableInvoicePaymentAccount(resolveInvoicePaymentAccount(company, currency), currency)) {
+    log.warn('Skipping reminder: no payment account configured for invoice currency', {
+      invoiceId: invoice.id,
+      invoiceNumber: invoice.invoice_number,
+      currency,
+    })
+    return { success: false, error: `INVOICE_PAYMENT_ACCOUNT_MISSING:${currency}` }
+  }
+
   const daysOverdue = calculateDaysOverdue(invoice.due_date)
 
   // Build action URL (public page for customer response)
@@ -267,6 +285,35 @@ export async function processOverdueReminders(): Promise<ProcessRemindersResult>
       continue
     }
 
+    // Payment-account gate, BEFORE any write: the fee journal entry and the
+    // invoice_reminders row below must not exist for a reminder that never
+    // goes out (that would book a 60 kr fee and burn the level for an email
+    // the customer never got). Same rule as invoice send: no usable account
+    // for the invoice currency means no reminder until the user configures
+    // one under Inställningar; the level stays open and fires next run.
+    const invoiceCurrency = invoice.currency
+    if (
+      !hasUsableInvoicePaymentAccount(
+        resolveInvoicePaymentAccount(company as CompanySettings, invoiceCurrency),
+        invoiceCurrency,
+      )
+    ) {
+      log.warn('Skipping reminder: no payment account configured for invoice currency', {
+        invoiceId: invoice.id,
+        invoiceNumber: invoice.invoice_number,
+        currency: invoiceCurrency,
+      })
+      results.push({
+        invoiceId: invoice.id,
+        invoiceNumber: invoice.invoice_number,
+        customerEmail: customer.email,
+        reminderLevel,
+        success: false,
+        error: `INVOICE_PAYMENT_ACCOUNT_MISSING:${invoiceCurrency}`,
+      })
+      continue
+    }
+
     // Race-window guard: re-check invoice status immediately before sending.
     // The cron runs at 08:00; a payment match arriving during the run shouldn't
     // produce a reminder for an already-paid invoice.