feat(accounting): split Incoming invoices vs Expenses - flags, schema, settings (stage 1)

Foundation for separating external supplier invoices from internal expenses,
per design review. This stage is additive + buildable; the service/route/UI
data rework follows in stage 2.

- Migration 126: incoming invoices own their payable on inbound_documents
  (supplier_paid/at/method/ref + disposition + tax_treatment + booking event_id
  + category_id + re-bill markup/linkage); expenses gain kind (amount/mileage/
  per_diem) + quantity + snapshotted rate_minor. Additive, hasColumn-guarded.
- Migration 127: seed `expenses` feature flag (default off) + accounting
  app_settings (accounting_km_rate_minor=70, accounting_per_diem_rate_minor=0,
  accounting_require_proof=false).
- Backend: `expenses` added to feature-flag known/defaults/dependency (forced
  off when the accounting master is off); new PUT /admin/settings/accounting
  (read via the generic GET /:type).
- Frontend: `expenses` flag (type + context + dependency); Features tab gets an
  Expenses sub-card; the Expenses sub-nav + route now gate on `expenses` (not
  incomingInvoices); AccountingIndex prefers inbox -> expenses -> tax.
- i18n: settings.features.expenses.* (EN + DE).

Verified: node -c; migration 124->126->127 harness (new columns, flag, settings
+ idempotency); en/de JSON valid; npm run build green.

backend/migrations/core/126_accounting_split_incoming_vs_expenses.js

@@ -0,0 +1,68 @@
+/**
+ * Migration 126: split Incoming invoices (external) from Expenses (internal).
+ *
+ * Incoming invoices now own their payable + disposition + re-bill on the
+ * `inbound_documents` row itself (no derived `expenses` row), so a supplier
+ * invoice lives ONLY in the inbox/incoming-invoices surface. The `expenses`
+ * table becomes internal-only (mileage / per-diem / cash with proof).
+ *
+ * Both can be booked to an event (event_id) or to the company (event_id NULL).
+ *
+ * Additive + hasColumn-guarded so it runs forward cleanly on dev (122-125 are
+ * already deployed there — no in-place edits).
+ */
+async function addColumn(knex, table, column, builder) {
+  // eslint-disable-next-line no-await-in-loop
+  if (!(await knex.schema.hasColumn(table, column))) {
+    await knex.schema.alterTable(table, builder);
+  }
+}
+
+exports.up = async function (knex) {
+  if (await knex.schema.hasTable('inbound_documents')) {
+    // Disposition + classification (now stored on the document itself).
+    await addColumn(knex, 'inbound_documents', 'disposition', (t) => t.string('disposition', 24));
+    await addColumn(knex, 'inbound_documents', 'tax_treatment', (t) => t.string('tax_treatment', 32));
+    await addColumn(knex, 'inbound_documents', 'category_id', (t) => t.integer('category_id').unsigned());
+    // Booking target: event_id NULL = booked to the company.
+    await addColumn(knex, 'inbound_documents', 'event_id', (t) => t.integer('event_id').unsigned());
+    // Re-bill (Weiterverrechnung) linkage + markup.
+    await addColumn(knex, 'inbound_documents', 'markup_type', (t) => t.string('markup_type', 8));
+    await addColumn(knex, 'inbound_documents', 'markup_percent', (t) => t.decimal('markup_percent', 5, 2));
+    await addColumn(knex, 'inbound_documents', 'markup_flat_minor', (t) => t.integer('markup_flat_minor'));
+    await addColumn(knex, 'inbound_documents', 'billed_invoice_id', (t) => t.integer('billed_invoice_id').unsigned());
+    await addColumn(knex, 'inbound_documents', 'billed_invoice_line_item_id', (t) => t.integer('billed_invoice_line_item_id').unsigned());
+    // Supplier payment (the payable is paid HERE, on the incoming invoice).
+    await addColumn(knex, 'inbound_documents', 'supplier_paid', (t) => t.boolean('supplier_paid').notNullable().defaultTo(false));
+    await addColumn(knex, 'inbound_documents', 'supplier_paid_at', (t) => t.timestamp('supplier_paid_at'));
+    await addColumn(knex, 'inbound_documents', 'supplier_payment_method', (t) => t.string('supplier_payment_method', 16));
+    await addColumn(knex, 'inbound_documents', 'supplier_payment_ref', (t) => t.string('supplier_payment_ref', 140));
+  }
+
+  if (await knex.schema.hasTable('expenses')) {
+    // Internal-expense kind + quantity-driven amount (mileage / per-diem).
+    await addColumn(knex, 'expenses', 'kind', (t) => t.string('kind', 16).notNullable().defaultTo('amount')); // amount|mileage|per_diem
+    await addColumn(knex, 'expenses', 'quantity', (t) => t.decimal('quantity', 10, 2)); // km count or number of days
+    await addColumn(knex, 'expenses', 'rate_minor', (t) => t.integer('rate_minor')); // snapshotted km/day rate
+  }
+};
+
+exports.down = async function (knex) {
+  const dropCols = async (table, cols) => {
+    if (!(await knex.schema.hasTable(table))) return;
+    for (const col of cols) {
+      // eslint-disable-next-line no-await-in-loop
+      if (await knex.schema.hasColumn(table, col)) {
+        // eslint-disable-next-line no-await-in-loop
+        await knex.schema.alterTable(table, (t) => t.dropColumn(col));
+      }
+    }
+  };
+  await dropCols('inbound_documents', [
+    'disposition', 'tax_treatment', 'category_id', 'event_id',
+    'markup_type', 'markup_percent', 'markup_flat_minor',
+    'billed_invoice_id', 'billed_invoice_line_item_id',
+    'supplier_paid', 'supplier_paid_at', 'supplier_payment_method', 'supplier_payment_ref',
+  ]);
+  await dropCols('expenses', ['kind', 'quantity', 'rate_minor']);
+};

backend/migrations/core/127_seed_expenses_flag_and_accounting_settings.js

@@ -0,0 +1,52 @@
+/**
+ * Migration 127: seed the `expenses` feature flag + the Accounting settings.
+ *
+ * - `expenses` feature flag (default OFF) — separate sub-toggle from
+ *   `incomingInvoices` under the Accounting master.
+ * - app_settings (setting_type='accounting'):
+ *     accounting_km_rate_minor      default 70   (CHF 0.70 / km — VERIFY with
+ *                                                 your Treuhänder, guideline only)
+ *     accounting_per_diem_rate_minor default 0   (admin sets a daily rate)
+ *     accounting_require_proof      default false (require a proof file on
+ *                                                  internal expenses)
+ *
+ * Idempotent: inserts only when missing.
+ */
+const ACCOUNTING_SETTINGS = [
+  { key: 'accounting_km_rate_minor', value: 70 },
+  { key: 'accounting_per_diem_rate_minor', value: 0 },
+  { key: 'accounting_require_proof', value: false },
+];
+
+exports.up = async function (knex) {
+  if (await knex.schema.hasTable('feature_flags')) {
+    const existing = await knex('feature_flags').where({ key: 'expenses' }).first();
+    if (!existing) await knex('feature_flags').insert({ key: 'expenses', value: false });
+  }
+
+  if (await knex.schema.hasTable('app_settings')) {
+    for (const s of ACCOUNTING_SETTINGS) {
+      // eslint-disable-next-line no-await-in-loop
+      const row = await knex('app_settings').where({ setting_key: s.key }).first();
+      if (!row) {
+        // eslint-disable-next-line no-await-in-loop
+        await knex('app_settings').insert({
+          setting_key: s.key,
+          setting_value: JSON.stringify(s.value),
+          setting_type: 'accounting',
+          created_at: new Date(),
+          updated_at: new Date(),
+        });
+      }
+    }
+  }
+};
+
+exports.down = async function (knex) {
+  if (await knex.schema.hasTable('feature_flags')) {
+    await knex('feature_flags').where({ key: 'expenses' }).del();
+  }
+  if (await knex.schema.hasTable('app_settings')) {
+    await knex('app_settings').whereIn('setting_key', ACCOUNTING_SETTINGS.map((s) => s.key)).del();
+  }
+};

backend/src/routes/adminFeatureFlags.js

@@ -66,10 +66,13 @@ const KNOWN_FLAGS = [
   // supplier invoices, expenses + re-bill, and the tax report (which
   // relocates here from CRM when this is on). Strictly opt-in.
   'accounting',
-  // Incoming invoices (migration 124) — supplier-invoice capture +
-  // expenses + re-bill. Accounting sub-feature; forced off when the
-  // `accounting` master is off.
+  // Incoming invoices (migration 124) — external supplier-invoice capture +
+  // re-bill. Accounting sub-feature; forced off when the `accounting` master
+  // is off.
   'incomingInvoices',
+  // Expenses (migration 127) — internal expenses (mileage / per-diem / cash).
+  // Separate Accounting sub-feature; forced off when `accounting` is off.
+  'expenses',
 ];
 
 // Spec defaults for any flag missing from the DB (e.g. a row added by a
@@ -94,6 +97,7 @@ const DEFAULT_FLAGS = {
   contracts: false,
   accounting: false,
   incomingInvoices: false,
+  expenses: false,
 };
 
 async function readAllFlags() {
@@ -120,6 +124,7 @@ function applyDependencyRules(flags) {
   if (out.accounting === false) {
     out.taxReport = false;
     out.incomingInvoices = false;
+    out.expenses = false;
   }
   // Clients parent flag is DERIVED from its children. Admins don't
   // toggle it directly in the Features tab — they enable a specific

backend/src/routes/adminSettings.js

@@ -234,6 +234,44 @@ router.put('/customer-surface', adminAuth, requirePermission('settings.edit'), a
   }
 });
 
+// Accounting settings (km rate, per-diem rate, require-proof). Read via the
+// generic GET /:type ('accounting'); this is the typed write. Rates are
+// integer minor units; verify legal/tax guidance with a Treuhaender.
+router.put('/accounting', adminAuth, requirePermission('settings.edit'), async (req, res) => {
+  try {
+    const updates = [];
+    const setInt = (key) => {
+      if (Object.prototype.hasOwnProperty.call(req.body, key)) {
+        const n = Math.max(0, Math.round(Number(req.body[key]) || 0));
+        updates.push({ setting_key: key, setting_value: JSON.stringify(n), setting_type: 'accounting' });
+      }
+    };
+    setInt('accounting_km_rate_minor');
+    setInt('accounting_per_diem_rate_minor');
+    if (Object.prototype.hasOwnProperty.call(req.body, 'accounting_require_proof')) {
+      updates.push({
+        setting_key: 'accounting_require_proof',
+        setting_value: JSON.stringify(!!req.body.accounting_require_proof),
+        setting_type: 'accounting',
+      });
+    }
+    for (const u of updates) {
+      const existing = await db('app_settings').where('setting_key', u.setting_key).first();
+      if (existing) {
+        await db('app_settings').where('setting_key', u.setting_key).update({
+          setting_value: u.setting_value, setting_type: u.setting_type, updated_at: new Date(),
+        });
+      } else {
+        await db('app_settings').insert({ ...u, created_at: new Date(), updated_at: new Date() });
+      }
+    }
+    res.json({ message: 'Accounting settings updated', updated: updates.map((u) => u.setting_key) });
+  } catch (error) {
+    console.error('Accounting settings save error:', error);
+    res.status(500).json({ error: 'Failed to save accounting settings' });
+  }
+});
+
 // Get settings by type
 router.get('/:type', adminAuth, requirePermission('settings.view'), async (req, res) => {
   try {

frontend/src/App.tsx

@@ -272,6 +272,8 @@ function App() {
                         <Route path="accounting" element={<AccountingLayout />}>
                           <Route element={<RequireFeature flag="incomingInvoices" />}>
                             <Route path="inbox" element={<AccountingInboxPage />} />
+                          </Route>
+                          <Route element={<RequireFeature flag="expenses" />}>
                             <Route path="expenses" element={<ExpensesLedgerPage />} />
                           </Route>
                           <Route element={<RequireFeature flag="taxReport" />}>

frontend/src/components/admin/AccountingLayout.tsx

@@ -41,7 +41,7 @@ export const AccountingLayout: React.FC = () => {
       to: '/admin/accounting/expenses',
       label: t('accounting.subnav.expenses', 'Expenses'),
       icon: Wallet,
-      featureFlag: 'incomingInvoices',
+      featureFlag: 'expenses',
     },
     {
       key: 'tax-report',
@@ -159,6 +159,7 @@ export const AccountingLayout: React.FC = () => {
 export const AccountingIndex: React.FC = () => {
   const { flags } = useFeatureFlags();
   if (flags.incomingInvoices) return <Navigate to="/admin/accounting/inbox" replace />;
+  if (flags.expenses) return <Navigate to="/admin/accounting/expenses" replace />;
   if (flags.taxReport) return <Navigate to="/admin/accounting/tax-report" replace />;
   return null;
 };

frontend/src/contexts/FeatureFlagsContext.tsx

@@ -48,9 +48,12 @@ export const DEFAULT_FLAGS: FeatureFlags = {
   // Accounting (migration 122). Top-level MASTER for the Accounting
   // section (separate from CRM). Sub-features below require it.
   accounting: false,
-  // Incoming invoices (migration 124) — supplier-invoice capture +
-  // expenses + re-bill. Accounting sub-feature; requires `accounting`.
+  // Incoming invoices (migration 124) — external supplier-invoice capture +
+  // re-bill. Accounting sub-feature; requires `accounting`.
   incomingInvoices: false,
+  // Expenses (migration 127) — internal expenses (mileage / per-diem / cash).
+  // Separate Accounting sub-feature; requires `accounting`.
+  expenses: false,
 };
 
 export const FEATURE_FLAGS_QUERY_KEY = ['feature-flags'] as const;
@@ -87,6 +90,7 @@ function applyDependencyRules(flags: FeatureFlags): FeatureFlags {
   if (out.accounting === false) {
     out.taxReport = false;
     out.incomingInvoices = false;
+    out.expenses = false;
   }
   // Clients parent flag is DERIVED from its children. Admins don't
   // toggle it directly — enabling any CRM-area sub-feature

frontend/src/features/settings/tabs/FeaturesTab.tsx

@@ -18,6 +18,7 @@ import {
   Calculator,
   Landmark,
   ScanLine,
+  Wallet,
 } from 'lucide-react';
 import { useTranslation } from 'react-i18next';
 import { Button, Card } from '../../../components/common';
@@ -331,6 +332,25 @@ export const FeaturesTab: React.FC = () => {
               'Enable Accounting first — Incoming invoices live in the Accounting section.',
             ) : undefined}
           />
+
+          <FeatureCard
+            icon={Wallet}
+            title={t('settings.features.expenses.title', 'Expenses')}
+            description={t(
+              'settings.features.expenses.description',
+              'Internal expenses (mileage, per-diem, cash) booked to an event or the company, with optional proof. Separate from incoming supplier invoices. Configure km / per-diem rates and the proof requirement in the Accounting settings tab.',
+            )}
+            status="new"
+            statusLabel={statusLabel('new')}
+            sidebarLabel={t('settings.features.expenses.sidebar', 'Expenses')}
+            enabled={staged.expenses}
+            onToggle={(next) => setFlag('expenses', next)}
+            disabled={!staged.accounting}
+            lockedReason={!staged.accounting ? t(
+              'settings.features.expenses.requiresAccounting',
+              'Enable Accounting first — Expenses live in the Accounting section.',
+            ) : undefined}
+          />
         </Section>
 
         {/* Insights & Access */}

frontend/src/i18n/locales/de.json

@@ -1650,6 +1650,12 @@
         "sidebar": "Eingang",
         "requiresAccounting": "Bitte zuerst Buchhaltung aktivieren — Eingangsrechnungen liegen im Buchhaltungsbereich."
       },
+      "expenses": {
+        "title": "Aufwände",
+        "description": "Interne Aufwände (Kilometer, Spesenpauschale, Barbelege), gebucht auf ein Event oder die Firma, mit optionalem Beleg. Getrennt von Eingangsrechnungen.",
+        "sidebar": "Aufwände",
+        "requiresAccounting": "Bitte zuerst Buchhaltung aktivieren — Aufwände liegen im Buchhaltungsbereich."
+      },
       "analytics": {
         "title": "Statistiken",
         "description": "Speichernutzung, Galerie-Aufrufe, Download-Zahlen und Statistiken pro Veranstaltung."

frontend/src/i18n/locales/en.json

@@ -1208,6 +1208,12 @@
         "sidebar": "Incoming",
         "requiresAccounting": "Enable Accounting first — Incoming invoices live in the Accounting section."
       },
+      "expenses": {
+        "title": "Expenses",
+        "description": "Internal expenses (mileage, per-diem, cash) booked to an event or the company, with optional proof. Separate from incoming supplier invoices.",
+        "sidebar": "Expenses",
+        "requiresAccounting": "Enable Accounting first — Expenses live in the Accounting section."
+      },
       "analytics": {
         "title": "Analytics",
         "description": "Storage usage, gallery views, download counts, and per-event stats."

frontend/src/services/featureFlags.service.ts

@@ -46,9 +46,12 @@ export type FeatureKey =
   // section (separate from CRM). Its sub-features (tax export, incoming
   // invoices) require it. Strictly opt-in.
   | 'accounting'
-  // Incoming invoices (migration 124) — supplier-invoice capture +
-  // expenses + re-bill. Accounting sub-feature; requires `accounting`.
-  | 'incomingInvoices';
+  // Incoming invoices (migration 124) — external supplier-invoice capture +
+  // re-bill. Accounting sub-feature; requires `accounting`.
+  | 'incomingInvoices'
+  // Expenses (migration 127) — internal expenses (mileage / per-diem / cash).
+  // Separate Accounting sub-feature; requires `accounting`.
+  | 'expenses';
 
 export type FeatureFlags = Record<FeatureKey, boolean>;