diff --git a/backend/__tests__/services/taxReportService.test.js b/backend/__tests__/services/taxReportService.test.js
index 12fc4ed6..50eb9fdd 100644
--- a/backend/__tests__/services/taxReportService.test.js
+++ b/backend/__tests__/services/taxReportService.test.js
@@ -371,7 +371,9 @@ describe('getTaxReport', () => {
     expect(out.summary).toMatchObject({
       incomeNetMinor: 10000, incomeVatMinor: 770, incomeGrossMinor: 10770,
       costNetMinor: 0, costVatMinor: 0, costGrossMinor: 0,
-      resultNetMinor: 10000, resultGrossMinor: 10770, vatPayableMinor: 770,
+      resultNetMinor: 10000, resultGrossMinor: 10770,
+      // VAT registration unconfigured in the test DB → refuse to compute payable.
+      vatRegistrationConfigured: false, vatPayableMinor: null,
     });
   });
 
@@ -433,7 +435,8 @@ describe('getTaxReport', () => {
     expect(out.summary).toMatchObject({
       incomeNetMinor: 100000, incomeVatMinor: 7700, incomeGrossMinor: 107700,
       costNetMinor: 25000, costVatMinor: 1540, costGrossMinor: 26540,
-      resultNetMinor: 75000, resultGrossMinor: 81160, vatPayableMinor: 6160,
+      resultNetMinor: 75000, resultGrossMinor: 81160,
+      vatRegistrationConfigured: false, vatPayableMinor: null,
     });
   });
 
diff --git a/backend/src/middleware/requireFeatureFlag.js b/backend/src/middleware/requireFeatureFlag.js
index 339fd9b5..c2637dae 100644
--- a/backend/src/middleware/requireFeatureFlag.js
+++ b/backend/src/middleware/requireFeatureFlag.js
@@ -6,27 +6,50 @@
  * hit must still be refused so a disabled feature is never actable. Mirrors the
  * truthy logic feature_flags uses everywhere (true | 1 | '1').
  *
+ * Cached: the accounting area alone is 10+ gated endpoints and the dashboard
+ * polls several, so a per-request DB read is wasteful. Flags change rarely and
+ * only via `PUT /admin/feature-flags`, which calls invalidateFeatureFlagCache()
+ * — so a short TTL is belt-and-braces against any other mutation path.
+ *
  * Several route files (adminLedger, adminExpenses) predate this and define an
  * identical local `requireFlag`; new gates should import this instead.
  */
 const { db } = require('../database/db');
 
+const TTL_MS = 10_000;
+const cache = new Map(); // key -> { enabled, expires }
+
+function flagEnabledFromRow(row) {
+  return !!(row && (row.value === true || row.value === 1 || row.value === '1'));
+}
+
+async function isFeatureEnabled(key) {
+  const now = Date.now();
+  const hit = cache.get(key);
+  if (hit && hit.expires > now) return hit.enabled;
+  const row = await db('feature_flags').where({ key }).first();
+  const enabled = flagEnabledFromRow(row);
+  cache.set(key, { enabled, expires: now + TTL_MS });
+  return enabled;
+}
+
+/** Clear the flag cache — call after any write to feature_flags. */
+function invalidateFeatureFlagCache() {
+  cache.clear();
+}
+
 function requireFeatureFlag(key, code) {
   return async (req, res, next) => {
     try {
-      const row = await db('feature_flags').where({ key }).first();
-      const enabled = row && (row.value === true || row.value === 1 || row.value === '1');
-      if (!enabled) {
-        return res.status(403).json({
-          error: `${key} feature is disabled`,
-          code: code || `${key.replace(/([a-z])([A-Z])/g, '$1_$2').toUpperCase()}_DISABLED`,
-        });
-      }
-      return next();
+      if (await isFeatureEnabled(key)) return next();
+      return res.status(403).json({
+        error: `${key} feature is disabled`,
+        code: code || `${key.replace(/([a-z])([A-Z])/g, '$1_$2').toUpperCase()}_DISABLED`,
+      });
     } catch (err) {
       return next(err);
     }
   };
 }
 
-module.exports = { requireFeatureFlag };
+module.exports = { requireFeatureFlag, isFeatureEnabled, invalidateFeatureFlagCache };
diff --git a/backend/src/routes/adminFeatureFlags.js b/backend/src/routes/adminFeatureFlags.js
index 6eda04b9..8c447f24 100644
--- a/backend/src/routes/adminFeatureFlags.js
+++ b/backend/src/routes/adminFeatureFlags.js
@@ -18,6 +18,7 @@ const router = express.Router();
 const { db, logActivity } = require('../database/db');
 const { adminAuth } = require('../middleware/auth');
 const { requirePermission } = require('../middleware/permissions');
+const { invalidateFeatureFlagCache } = require('../middleware/requireFeatureFlag');
 const logger = require('../utils/logger');
 
 // Canonical flag list. Keep in sync with frontend
@@ -226,6 +227,10 @@ router.put('/', adminAuth, requirePermission('settings.edit'), async (req, res)
       }
     });
 
+    // Drop the requireFeatureFlag middleware's short-TTL cache so a toggle takes
+    // effect immediately instead of after ≤10s.
+    invalidateFeatureFlagCache();
+
     await logActivity(
       'feature_flags_updated',
       { changed, actor: adminUsername },
diff --git a/backend/src/routes/adminSettings.js b/backend/src/routes/adminSettings.js
index 350d5dc7..87040945 100644
--- a/backend/src/routes/adminSettings.js
+++ b/backend/src/routes/adminSettings.js
@@ -19,6 +19,7 @@ const {
   getRawPublicSiteSettings,
 } = require('../services/publicSiteService');
 const { sanitizeCss } = require('../utils/cssSanitizer');
+const { upsertAppSetting } = require('../utils/appSettings');
 const { clearShareLinkSettingsCache } = require('../services/shareLinkService');
 const { resetSecurityConfigCache } = require('../utils/authSecurity');
 const router = express.Router();
@@ -211,19 +212,7 @@ router.put('/customer-surface', adminAuth, requirePermission('settings.edit'), a
     }
 
     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 {
-        // app_settings has no created_at column (see src/database/db.js: only
-        // setting_key/value/type + updated_at). Inserting created_at errors —
-        // which broke first-time keys like the VAT-registration toggle.
-        await db('app_settings').insert({ ...u, updated_at: new Date() });
-      }
+      await upsertAppSetting(u.setting_key, u.setting_value, u.setting_type);
     }
 
     // Clear the public-site cache so any consumer relying on it
@@ -282,17 +271,7 @@ router.put('/accounting', adminAuth, requirePermission('settings.edit'), async (
       });
     }
     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 {
-        // app_settings has no created_at column (see src/database/db.js: only
-        // setting_key/value/type + updated_at). Inserting created_at errors —
-        // which broke first-time keys like the VAT-registration toggle.
-        await db('app_settings').insert({ ...u, updated_at: new Date() });
-      }
+      await upsertAppSetting(u.setting_key, u.setting_value, u.setting_type);
     }
     res.json({ message: 'Accounting settings updated', updated: updates.map((u) => u.setting_key) });
   } catch (error) {
diff --git a/backend/src/routes/customer.js b/backend/src/routes/customer.js
index f9ac8796..d2b827d9 100644
--- a/backend/src/routes/customer.js
+++ b/backend/src/routes/customer.js
@@ -24,6 +24,19 @@ const { customerAuth } = require('../middleware/customerAuth');
 const { setGalleryAuthCookies } = require('../utils/tokenUtils');
 const customerAccountsService = require('../services/customerAccountsService');
 
+// Gate a customer-facing route on BOTH the global master flag AND the
+// per-customer override — getEffectiveFeaturesForCustomer combines them, so an
+// admin disabling e.g. Bills globally is honoured even when feature_bills=true
+// on the row. Sends the 403 and returns false on denial; true if allowed.
+async function customerFeatureAllowed(req, res, featureKey, label) {
+  const eff = await customerAccountsService.getEffectiveFeaturesForCustomer(req.customer.id);
+  if (!eff || !eff[featureKey]) {
+    res.status(403).json({ error: `${label} are disabled for this account`, code: 'CUSTOMER_FEATURE_DISABLED' });
+    return false;
+  }
+  return true;
+}
+
 /**
  * Customer-side password policy mirrors the one in customerAuth.js — kept
  * deliberately simple (8 chars, one uppercase, one digit) since a customer
@@ -380,11 +393,8 @@ router.post('/profile/password', [
 router.get('/quotes', customerAuth, async (req, res) => {
   try {
     const { db: dbi } = require('../database/db');
-    // Customer-feature gate. is_active is enforced by customerAuth.
-    const customer = await dbi('customer_accounts').where({ id: req.customer.id }).first();
-    if (!customer || customer.feature_quotes === false || customer.feature_quotes === 0) {
-      return res.status(403).json({ error: 'Quotes are disabled for this account', code: 'CUSTOMER_FEATURE_DISABLED' });
-    }
+    // Customer-feature gate — master flag AND per-customer override.
+    if (!(await customerFeatureAllowed(req, res, 'quotes', 'Quotes'))) return;
     const rows = await dbi('quotes')
       .where({ customer_account_id: req.customer.id })
       // Hide drafts — they're admin scratch work; nothing has been
@@ -459,10 +469,8 @@ router.get('/quotes', customerAuth, async (req, res) => {
 router.get('/invoices', customerAuth, async (req, res) => {
   try {
     const { db: dbi } = require('../database/db');
-    const customer = await dbi('customer_accounts').where({ id: req.customer.id }).first();
-    if (!customer || customer.feature_bills === false || customer.feature_bills === 0) {
-      return res.status(403).json({ error: 'Invoices are disabled for this account', code: 'CUSTOMER_FEATURE_DISABLED' });
-    }
+    // Customer-feature gate — master flag AND per-customer override.
+    if (!(await customerFeatureAllowed(req, res, 'bills', 'Invoices'))) return;
     // Visibility rules for the customer-facing list:
     //   - Hide `scheduled` always (drafts the admin is still tweaking).
     //   - Show `sent`, `overdue`, `paid` always (the customer's
@@ -551,14 +559,8 @@ router.get('/invoices', customerAuth, async (req, res) => {
 router.get('/quotes/:id/pdf', customerAuth, async (req, res) => {
   try {
     const { db: dbi } = require('../database/db');
-    // Feature-gate identically to /quotes (list endpoint). req.customer does
-    // NOT carry feature_* columns (customerAuth only selects identity), so we
-    // read the row here — the previous req.customer.feature_quotes check was a
-    // silent no-op (always undefined).
-    const account = await dbi('customer_accounts').where({ id: req.customer.id }).first();
-    if (!account || account.feature_quotes === false || account.feature_quotes === 0) {
-      return res.status(403).json({ error: 'Quotes are disabled for this account', code: 'CUSTOMER_FEATURE_DISABLED' });
-    }
+    // Feature-gate — master flag AND per-customer override.
+    if (!(await customerFeatureAllowed(req, res, 'quotes', 'Quotes'))) return;
     const quote = await dbi('quotes')
       .where({ id: parseInt(req.params.id, 10), customer_account_id: req.customer.id })
       .first();
@@ -588,12 +590,8 @@ router.get('/quotes/:id/pdf', customerAuth, async (req, res) => {
 router.get('/invoices/:id/pdf', customerAuth, async (req, res) => {
   try {
     const { db: dbi } = require('../database/db');
-    // Feature-gate identically to /invoices (list endpoint) — a direct hit must
-    // not download an invoice PDF when Bills is disabled for the account.
-    const account = await dbi('customer_accounts').where({ id: req.customer.id }).first();
-    if (!account || account.feature_bills === false || account.feature_bills === 0) {
-      return res.status(403).json({ error: 'Invoices are disabled for this account', code: 'CUSTOMER_FEATURE_DISABLED' });
-    }
+    // Feature-gate — master flag AND per-customer override.
+    if (!(await customerFeatureAllowed(req, res, 'bills', 'Invoices'))) return;
     const invoice = await dbi('invoices')
       .where({ id: parseInt(req.params.id, 10), customer_account_id: req.customer.id })
       .first();
@@ -633,12 +631,8 @@ router.get('/contracts', customerAuth, async (req, res) => {
       // Feature not migrated on this install yet.
       return res.json({ contracts: [] });
     }
-    // Per-customer contracts gate (migration 131) — mirrors /quotes + /invoices
-    // so a direct hit is refused when Contracts is off for the account.
-    const account = await dbi('customer_accounts').where({ id: req.customer.id }).first();
-    if (!account || account.feature_contracts === false || account.feature_contracts === 0) {
-      return res.status(403).json({ error: 'Contracts are disabled for this account', code: 'CUSTOMER_FEATURE_DISABLED' });
-    }
+    // Contracts gate — master flag AND per-customer override (migration 131).
+    if (!(await customerFeatureAllowed(req, res, 'contracts', 'Contracts'))) return;
     const rows = await dbi('contracts')
       .where({ customer_account_id: req.customer.id })
       .whereNotIn('status', ['draft'])
@@ -696,10 +690,8 @@ router.get('/contracts/:id/pdf', customerAuth, async (req, res) => {
     if (!(await dbi.schema.hasTable('contracts'))) {
       return res.status(404).json({ error: 'Contract not found' });
     }
-    const account = await dbi('customer_accounts').where({ id: req.customer.id }).first();
-    if (!account || account.feature_contracts === false || account.feature_contracts === 0) {
-      return res.status(403).json({ error: 'Contracts are disabled for this account', code: 'CUSTOMER_FEATURE_DISABLED' });
-    }
+    // Contracts gate — master flag AND per-customer override.
+    if (!(await customerFeatureAllowed(req, res, 'contracts', 'Contracts'))) return;
     const contract = await dbi('contracts')
       .where({ id: parseInt(req.params.id, 10), customer_account_id: req.customer.id })
       .first();
diff --git a/backend/src/services/expenseService.js b/backend/src/services/expenseService.js
index fdff8ab6..d15b7cc8 100644
--- a/backend/src/services/expenseService.js
+++ b/backend/src/services/expenseService.js
@@ -153,7 +153,10 @@ async function recordInboundDocument({ source, filePath, originalFilename, mimeT
     status: duplicateOfId ? 'duplicate' : 'unsorted',
     parse_status: 'pending',
     parse_method: 'none',
-    page_count: pageCount,
+    // Cap stored page_count to the renderable max (rasterizeService
+    // MAX_RENDERABLE_PAGES) so a hostile high-page PDF can't drive an
+    // unbounded inbox pager (PR #622 concern 6).
+    page_count: pageCount != null ? Math.min(pageCount, 200) : null,
     duplicate_of_id: duplicateOfId,
     created_by_admin_id: adminId || null,
     created_at: now,
diff --git a/backend/src/services/rasterizeService.js b/backend/src/services/rasterizeService.js
index 77a84e8d..a7c8f3cb 100644
--- a/backend/src/services/rasterizeService.js
+++ b/backend/src/services/rasterizeService.js
@@ -22,6 +22,10 @@ const logger = require('../utils/logger');
 
 const RENDER_TIMEOUT_MS = 25000;
 const RENDER_DPI = 150;
+// Per-file resource bound (PR #622 concern 6): pages render one-per-request, so
+// a 1000-page hostile PDF could otherwise be walked page-by-page. Refuse to
+// render beyond this — the inbox pager is capped to match.
+const MAX_RENDERABLE_PAGES = 200;
 
 function renderedDir(docId) {
   return path.join(getStoragePath(), 'business-docs', 'inbound', 'rendered', String(docId));
@@ -41,6 +45,9 @@ function execFileAsync(cmd, args, opts) {
  * @throws AppError 503 when pdftoppm is unavailable, 500 on render failure.
  */
 async function getRenderedPagePath(docId, pdfPath, pageNum) {
+  if (!Number.isInteger(pageNum) || pageNum < 1 || pageNum > MAX_RENDERABLE_PAGES) {
+    throw new AppError(`Page out of range (1–${MAX_RENDERABLE_PAGES})`, 400, 'PAGE_OUT_OF_RANGE');
+  }
   const dir = renderedDir(docId);
   const outPng = path.join(dir, `page-${pageNum}.png`);
   if (fs.existsSync(outPng)) return outPng;
diff --git a/backend/src/services/taxReportService.js b/backend/src/services/taxReportService.js
index c08c2ce6..31ebda84 100644
--- a/backend/src/services/taxReportService.js
+++ b/backend/src/services/taxReportService.js
@@ -502,10 +502,14 @@ async function getTaxReport({ from, to, currency, includeCosts = true } = {}) {
     // business doesn't file VAT (payable = 0); when registered it's output VAT
     // minus the RECLAIMABLE input VAT only (foreign non-reclaimable cost VAT is
     // not deducted). Guideline figure — verify with your Treuhänder.
-    let vatRegistered = await getVatRegisteredSetting();
-    // Unset → preserve prior behaviour: if the business charged output VAT this
-    // period it's effectively registered; otherwise treat as small-business.
-    if (vatRegistered === null) vatRegistered = grandTotalVat > 0;
+    // PR #622 concern 4: when VAT registration is UNSET we must NOT guess from
+    // `grandTotalVat > 0` — a quarter with all-exempt cross-border sales has zero
+    // output VAT and would silently flip to "not registered", hiding the reclaim.
+    // Treat null as "not configured": refuse to compute a payable, surface a
+    // warning in the UI instead.
+    const vatRegisteredSetting = await getVatRegisteredSetting();
+    const vatRegistrationConfigured = vatRegisteredSetting !== null;
+    const vatRegistered = vatRegisteredSetting === true;
     const reclaimableInputVat = costs.reclaimableVat != null ? costs.reclaimableVat : costs.totalVat;
 
     // Summary: income vs cost vs result. Result = a simplified
@@ -520,7 +524,12 @@ async function getTaxReport({ from, to, currency, includeCosts = true } = {}) {
       resultNetMinor: grandTotalNet - costs.totalNet,
       resultGrossMinor: grandTotal - costs.totalGross,
       vatRegistered,
-      vatPayableMinor: vatRegistered ? (grandTotalVat - reclaimableInputVat) : 0,
+      vatRegistrationConfigured,
+      // null (not 0) when registration is unconfigured — the UI renders "—" + a
+      // "configure VAT registration" warning rather than a misleading number.
+      vatPayableMinor: !vatRegistrationConfigured
+        ? null
+        : (vatRegistered ? (grandTotalVat - reclaimableInputVat) : 0),
     };
 
     // Unified ledger (#5 — one typed, signed, sortable list). Outgoing
diff --git a/backend/src/utils/appSettings.js b/backend/src/utils/appSettings.js
index 354eaa05..29a989d6 100644
--- a/backend/src/utils/appSettings.js
+++ b/backend/src/utils/appSettings.js
@@ -35,4 +35,22 @@ async function getAppSetting(key, defaultValue = null) {
   }
 }
 
-module.exports = { getAppSetting };
+/**
+ * Schema-correct upsert into app_settings. The table has NO `created_at`
+ * column (only setting_key/setting_value/setting_type + updated_at — see
+ * src/database/db.js), so inserting created_at throws and silently breaks the
+ * FIRST save of any new key. Centralised here so route authors can't
+ * re-introduce that bug (PR #622 concern 5). `setting_value` is expected to be
+ * already JSON-stringified, matching getAppSetting's JSON.parse on read.
+ */
+async function upsertAppSetting(setting_key, setting_value, setting_type, conn = db) {
+  const existing = await conn('app_settings').where({ setting_key }).first();
+  if (existing) {
+    await conn('app_settings').where({ setting_key })
+      .update({ setting_value, setting_type, updated_at: new Date() });
+  } else {
+    await conn('app_settings').insert({ setting_key, setting_value, setting_type, updated_at: new Date() });
+  }
+}
+
+module.exports = { getAppSetting, upsertAppSetting };
diff --git a/frontend/src/i18n/locales/de.json b/frontend/src/i18n/locales/de.json
index 6670a57a..f3f90e36 100644
--- a/frontend/src/i18n/locales/de.json
+++ b/frontend/src/i18n/locales/de.json
@@ -3974,7 +3974,8 @@
       "income": "Einnahmen",
       "costs": "Ausgaben",
       "result": "Ergebnis",
-      "vatPayable": "MWST-Zahllast (Umsatz- − Vorsteuer)"
+      "vatPayable": "MWST-Zahllast (Umsatz- − Vorsteuer)",
+      "vatUnconfigured": "Die MWST-Registrierung ist nicht konfiguriert, daher kann die MWST-Zahllast nicht berechnet werden. Lege sie unter Einstellungen → Buchhaltung fest."
     },
     "cost": {
       "source": "Art",
diff --git a/frontend/src/i18n/locales/en.json b/frontend/src/i18n/locales/en.json
index 5b4f48e2..86281af7 100644
--- a/frontend/src/i18n/locales/en.json
+++ b/frontend/src/i18n/locales/en.json
@@ -3974,7 +3974,8 @@
       "income": "Income",
       "costs": "Costs",
       "result": "Result",
-      "vatPayable": "VAT payable (output − input)"
+      "vatPayable": "VAT payable (output − input)",
+      "vatUnconfigured": "VAT registration isn’t configured, so VAT payable can’t be computed. Set it under Settings → Accounting."
     },
     "cost": {
       "source": "Type",
diff --git a/frontend/src/pages/admin/clients/TaxReportPage.tsx b/frontend/src/pages/admin/clients/TaxReportPage.tsx
index 51f02487..d74aca29 100644
--- a/frontend/src/pages/admin/clients/TaxReportPage.tsx
+++ b/frontend/src/pages/admin/clients/TaxReportPage.tsx
@@ -442,9 +442,17 @@ export const TaxReportPage: React.FC = () => {
                   <div className="flex justify-between gap-3 text-xs text-neutral-500 dark:text-neutral-400">
                     <span>{t('taxReport.summary.vatPayable', 'VAT payable (output − input)')}</span>
                     <span className="tabular-nums">
-                      {formatMinor(report.summary.vatPayableMinor, report.currency, intlLocale)}
+                      {report.summary.vatRegistrationConfigured === false || report.summary.vatPayableMinor == null
+                        ? '—'
+                        : formatMinor(report.summary.vatPayableMinor, report.currency, intlLocale)}
                     </span>
                   </div>
+                  {report.summary.vatRegistrationConfigured === false && (
+                    <p className="flex items-start gap-1.5 text-xs text-amber-600 dark:text-amber-400 pt-1">
+                      <AlertCircle className="w-3.5 h-3.5 flex-shrink-0 mt-0.5" />
+                      <span>{t('taxReport.summary.vatUnconfigured', 'VAT registration isn’t configured, so VAT payable can’t be computed. Set it under Settings → Accounting.')}</span>
+                    </p>
+                  )}
                 </div>
               </div>
             )}
diff --git a/frontend/src/services/taxReport.service.ts b/frontend/src/services/taxReport.service.ts
index eeffd28f..94eac99b 100644
--- a/frontend/src/services/taxReport.service.ts
+++ b/frontend/src/services/taxReport.service.ts
@@ -84,7 +84,12 @@ export interface TaxReportSummary {
   costGrossMinor: number;
   resultNetMinor: number;
   resultGrossMinor: number;
-  vatPayableMinor: number;
+  /** Whether `accounting_vat_registered` is configured. When false, the
+   *  report refuses to guess and `vatPayableMinor` is null. */
+  vatRegistrationConfigured?: boolean;
+  /** output VAT − reclaimable input VAT; `null` when VAT registration is
+   *  unconfigured (the UI shows "—" + a warning instead of a guess). */
+  vatPayableMinor: number | null;
 }
 
 /** A single row of the unified ledger (#5). Outgoing invoices carry