fix(invoices): auto-track due date from send date + payment term

Due date now derives from (scheduled send date else issue date) plus the
selected Net-days template, both in the editor and on save. The bill
editor renders it read-only with an Override toggle for manual entry;
existing invoices preserve their stored due date. Backend adds a single
resolveNetDays resolver that honors the split payment-net-days template
(previously only the legacy FK was read) and the
crm_payment_default_net_days setting, used by createInvoice and the
installment-spawn path alike.

backend/src/services/invoiceService.js

@@ -104,6 +104,46 @@ function computeDueDate(scheduledSendAt, netDays = 30) {
   return new Date(scheduledSendAt.getTime() + ensureInt(netDays) * 24 * 60 * 60 * 1000);
 }
 
+/**
+ * Resolve the net-days a new invoice's due date should be anchored to.
+ * Single source of truth so the editor (split picker), legacy callers,
+ * and quote→invoice conversion all land on the same number. Priority:
+ *
+ *   1. `payload.netDays` — explicit caller override (installment spawn
+ *      passes the snapshot's net_days here).
+ *   2. Split picker (migration 124): payment_net_days_templates.net_days
+ *      via `payload.paymentNetDaysTemplateId`. This is what the bill
+ *      editor actually sends; the old code only read the legacy FK and
+ *      so silently ignored Net 60 / 90 selections.
+ *   3. Legacy single FK: payment_term_templates.net_days via
+ *      `payload.paymentTermTemplateId`.
+ *   4. The `crm_payment_default_net_days` setting (admin-configured).
+ *   5. 30 — historical hard default.
+ */
+async function resolveNetDays(payload, trx = db) {
+  if (payload && payload.netDays != null && payload.netDays !== '') {
+    const n = ensureInt(payload.netDays);
+    if (n) return n;
+  }
+  if (payload && payload.paymentNetDaysTemplateId) {
+    const probe = await trx('payment_net_days_templates')
+      .where({ id: payload.paymentNetDaysTemplateId })
+      .select('net_days')
+      .first();
+    if (probe && probe.net_days != null) return ensureInt(probe.net_days) || 30;
+  }
+  if (payload && payload.paymentTermTemplateId) {
+    const probe = await trx('payment_term_templates')
+      .where({ id: payload.paymentTermTemplateId })
+      .select('net_days')
+      .first();
+    if (probe && probe.net_days != null) return ensureInt(probe.net_days) || 30;
+  }
+  const setting = ensureInt(await getAppSetting('crm_payment_default_net_days'));
+  if (setting) return setting;
+  return 30;
+}
+
 /**
  * Resolve the deal_uuid for a new invoice row (migration 140). Priority:
  *
@@ -642,18 +682,13 @@ async function createInvoice(payload, adminId, trx = db) {
   // used `invoiceNumber` here.
   const issueDate = payload.issueDate || new Date().toISOString().slice(0, 10);
   const scheduledSendAt = payload.scheduledSendAt ? new Date(payload.scheduledSendAt) : null;
-  // Resolve the selected payment-term template's net_days BEFORE
-  // computing the due date so Net 60 / 90 templates actually push
-  // the due date out. Falls back to 30 when no template is set
-  // (matches the historical default).
-  let resolvedNetDays = 30;
-  if (payload.paymentTermTemplateId) {
-    const probe = await trx('payment_term_templates')
-      .where({ id: payload.paymentTermTemplateId })
-      .select('net_days')
-      .first();
-    if (probe && probe.net_days != null) resolvedNetDays = ensureInt(probe.net_days) || 30;
-  }
+  // Resolve net_days BEFORE computing the due date so Net 60 / 90
+  // selections actually push the due date out. resolveNetDays honors
+  // the split picker FK the editor sends, the legacy single FK, and
+  // the crm_payment_default_net_days setting (see helper). The clock
+  // starts on the SEND date when the invoice is scheduled, otherwise
+  // the issue date — so a future send pushes the due date out too.
+  const resolvedNetDays = await resolveNetDays(payload, trx);
   const dueDate = payload.dueDate || computeDueDate(scheduledSendAt || new Date(issueDate), resolvedNetDays)
     .toISOString().slice(0, 10);
 
@@ -927,10 +962,13 @@ async function spawnInstallmentInvoices({ trx, eventId, quoteId, customer, curre
   }
 
   // netDays drives the due-date offset on every scheduled invoice
-  // created here. Defaults to 30 when the caller doesn't pass one;
-  // callers in quoteService now pass the converting quote's
-  // payment-term net_days so Net 60 / 90 templates flow through.
-  const resolvedNetDays = ensureInt(netDays) || 30;
+  // created here. Callers in quoteService pass the converting quote's
+  // payment-term net_days so Net 60 / 90 templates flow through; when
+  // absent we fall back to the crm_payment_default_net_days setting
+  // (then 30) rather than silently using 30, matching createInvoice.
+  const resolvedNetDays = ensureInt(netDays)
+    || ensureInt(await getAppSetting('crm_payment_default_net_days'))
+    || 30;
   const total = installments.length;
   const acceptanceTime = new Date();
   const invoiceIds = [];

frontend/src/i18n/locales/de.json

@@ -3512,6 +3512,8 @@
       "total": "Gesamt",
       "sourceQuote": "Vom Angebot",
       "issueDate": "Ausgestellt am",
+      "dueDateOverrideOn": "Manuelles Fälligkeitsdatum — Häkchen entfernen, um es automatisch aus Versanddatum + Zahlungsziel zu berechnen",
+      "dueDateOverrideOff": "Automatisch aus Versanddatum + Zahlungsziel — ankreuzen, um es manuell zu setzen",
       "scheduledSendAt": "Geplanter Versand (optional)",
       "installment": "Rate",
       "paid": "Bezahlt",

frontend/src/i18n/locales/en.json

@@ -3557,6 +3557,8 @@
     "field": {
       "issueDate": "Issued",
       "dueDate": "Due",
+      "dueDateOverrideOn": "Manual due date — untick to auto-set from send date + payment term",
+      "dueDateOverrideOff": "Auto from send date + payment term — tick to set manually",
       "scheduledSendAt": "Scheduled send",
       "installment": "Installment",
       "total": "Total",

frontend/src/pages/admin/bills/BillEditorPage.tsx

@@ -48,6 +48,12 @@ export const BillEditorPage: React.FC = () => {
   const [currency, setCurrency] = useState('CHF');
   const [issueDate, setIssueDate] = useState(new Date().toISOString().slice(0, 10));
   const [dueDate, setDueDate] = useState('');
+  // Due date is normally view-only: it auto-tracks (send date else issue
+  // date) + the selected Net-days template, so the payment clock starts
+  // on the day the invoice actually goes out. Flipping this lets the
+  // admin type a different date by hand; we keep it pinned so the auto
+  // effect below stops clobbering their value.
+  const [dueDateOverridden, setDueDateOverridden] = useState(false);
   const [scheduledSendAt, setScheduledSendAt] = useState('');
   // null = inherit profile default at render time. 'none' / 'swiss' /
   // 'epc' = explicit per-invoice override. (Existing invoices that
@@ -124,6 +130,10 @@ export const BillEditorPage: React.FC = () => {
       setCurrency(inv.currency);
       setIssueDate(inv.issueDate);
       setDueDate(inv.dueDate);
+      // The invoice already carries a due date — preserve it rather than
+      // letting the auto effect recompute and surprise the admin. They
+      // can untick "Override" to re-enable auto-tracking.
+      setDueDateOverridden(true);
       setScheduledSendAt(inv.scheduledSendAt ? inv.scheduledSendAt.slice(0, 16) : '');
       // Preserve null when the saved invoice has no explicit format —
       // it inherits the profile default at render time.
@@ -317,6 +327,25 @@ export const BillEditorPage: React.FC = () => {
     setPaymentTimingTemplateId((prev) => prev ?? defaultTiming.id);
   }, [isEdit, netDaysTemplates, timingTemplates, appSettings]);
 
+  // Auto-track the due date off (scheduled send date else issue date) +
+  // the selected Net-days template, mirroring the backend's
+  // computeDueDate. The clock starts the day the invoice goes out, so
+  // scheduling a future send pushes the due date out with it. Skipped
+  // once the admin overrides the field by hand. Date math is in UTC to
+  // match the backend (which parses the YYYY-MM-DD base as UTC midnight).
+  useEffect(() => {
+    if (dueDateOverridden) return;
+    const base = (scheduledSendAt ? scheduledSendAt.slice(0, 10) : issueDate) || '';
+    if (!/^\d{4}-\d{2}-\d{2}$/.test(base)) return;
+    const tpl = netDaysTemplates?.templates?.find((t) => t.id === paymentNetDaysTemplateId);
+    const netDays = tpl?.netDays != null
+      ? Number(tpl.netDays)
+      : Number(appSettings?.crm_payment_default_net_days) || 30;
+    const d = new Date(`${base}T00:00:00Z`);
+    d.setUTCDate(d.getUTCDate() + netDays);
+    setDueDate(d.toISOString().slice(0, 10));
+  }, [dueDateOverridden, scheduledSendAt, issueDate, paymentNetDaysTemplateId, netDaysTemplates, appSettings]);
+
   const buildPayload = (): InvoiceCreatePayload => ({
     customerAccountId: customerId || 0,
     currency,
@@ -501,7 +530,25 @@ export const BillEditorPage: React.FC = () => {
         <h3 className="font-semibold mb-2">{t('bills.section.details', 'Details')}</h3>
         <div className="grid grid-cols-1 md:grid-cols-2 gap-3">
           <LocalizedDateInput label={t('bills.field.issueDate', 'Issue date') as string} value={issueDate} onChange={setIssueDate} />
-          <LocalizedDateInput label={t('bills.field.dueDate', 'Due date') as string} value={dueDate} onChange={setDueDate} />
+          <div>
+            <LocalizedDateInput
+              label={t('bills.field.dueDate', 'Due date') as string}
+              value={dueDate}
+              onChange={setDueDate}
+              disabled={!dueDateOverridden}
+            />
+            <label className="mt-1.5 flex items-center gap-2 text-xs text-neutral-600 dark:text-neutral-400">
+              <input
+                type="checkbox"
+                checked={dueDateOverridden}
+                onChange={(e) => setDueDateOverridden(e.target.checked)}
+                className="rounded border-neutral-300 dark:border-neutral-600"
+              />
+              {dueDateOverridden
+                ? t('bills.field.dueDateOverrideOn', 'Manual due date — untick to auto-set from send date + payment term')
+                : t('bills.field.dueDateOverrideOff', 'Auto from send date + payment term — tick to set manually')}
+            </label>
+          </div>
           <Input type="datetime-local" label={t('bills.field.scheduledSendAt', 'Scheduled send (optional)') as string}
             value={scheduledSendAt} onChange={(e) => setScheduledSendAt(e.target.value)} />
           <div>