diff --git a/e2e/admin-dev-bypass.spec.ts b/e2e/admin-dev-bypass.spec.ts
new file mode 100644
index 0000000..d47230a
--- /dev/null
+++ b/e2e/admin-dev-bypass.spec.ts
@@ -0,0 +1,27 @@
+import { expect, test } from '@playwright/test';
+
+/**
+ * Track Q Q2 / frontend backlog F59: past "verified live" admin claims were
+ * code-inspection only, because /backoffice needs a real Telegram login this
+ * suite cannot perform. ?devBypassAdmin=true (src/app/app.ts, gated by
+ * Angular's isDevMode() at runtime in @marketplaces/auth's
+ * AdminAuthService.devBypassLogin - not just build-time, and a no-op in any
+ * production build) is the existing, already-shipped answer - this test just
+ * proves it actually gets an E2E run into the admin shell.
+ */
+test.describe('admin dev bypass', () => {
+  test('?devBypassAdmin=true reaches the admin shell without a Telegram login', async ({ page }) => {
+    await page.goto('/?devBypassAdmin=true');
+    await page.waitForLoadState('networkidle');
+
+    // The bypass alone doesn't navigate anywhere - it only activates the
+    // session, so the admin surface has to be reached directly afterwards.
+    await page.goto('/admin/dashboard');
+    await page.waitForLoadState('networkidle');
+
+    // A real Telegram-gated admin route would redirect to a login dialog;
+    // reaching dashboard content is the actual proof the bypass worked.
+    await expect(page).not.toHaveURL(/login/i);
+    await expect(page.locator('body')).not.toContainText(/scan.*qr|log in with telegram/i);
+  });
+});
diff --git a/e2e/checkout-idempotent-click.spec.ts b/e2e/checkout-idempotent-click.spec.ts
new file mode 100644
index 0000000..f3f58d6
--- /dev/null
+++ b/e2e/checkout-idempotent-click.spec.ts
@@ -0,0 +1,76 @@
+import { Page, Route, expect, test } from '@playwright/test';
+
+/**
+ * Track Q Q5 / frontend backlog F62: "repeat webhook and double-click create
+ * exactly one order." The webhook-idempotency half is a backend contract
+ * (PHASE-1-MONEY-FX-PAYMENTS-CONTRACT.md §6.3, provider + providerEventId as
+ * the dedup key) this suite cannot exercise without a live backend. This
+ * test covers the half that IS frontend-testable: a double-click on the
+ * checkout button must not fire two checkout-session requests.
+ */
+
+const FAKE_ITEM = {
+  categoryID: 1, itemID: 5151, name: 'Idempotency Test Item', photos: null,
+  description: '', currency: 'RUB', price: 500, discount: 0, rating: 0,
+  callbacks: null, questions: null, quantity: 1,
+};
+
+test('double-clicking checkout sends exactly one checkout-session request', async ({ page, context }) => {
+  await page.addInitScript(item => {
+    window.localStorage.setItem('marketplace_cart', JSON.stringify([item]));
+  }, FAKE_ITEM);
+
+  await context.addCookies([{ name: 'webSessionID', value: 'e2e-fake-session', domain: 'localhost', path: '/' }]);
+  await page.route('**/users/sessions/**', route =>
+    route.fulfill({
+      status: 200, contentType: 'application/json',
+      body: JSON.stringify({ sessionId: 'e2e-fake-session', status: 'active', username: 'e2e_user', userId: 1 }),
+    }),
+  );
+  await page.route('**/api/v2/pricing/fx-quote**', route =>
+    route.fulfill({
+      status: 200, contentType: 'application/json',
+      body: JSON.stringify({ quoteId: 'fxq_e2e', base: 'RUB', quote: 'RUB', rate: 1, source: 'e2e', observedAt: new Date().toISOString(), expiresAt: new Date(Date.now() + 300000).toISOString() }),
+    }),
+  );
+
+  let checkoutRequestCount = 0;
+  await page.route('**/api/v2/storefront/checkout', async (route: Route) => {
+    checkoutRequestCount += 1;
+    // Deliberately slow, so a real double-click's second event has to land
+    // while the first request is still in flight - the exact race this test
+    // exists to catch.
+    await new Promise(resolve => setTimeout(resolve, 300));
+    route.fulfill({
+      status: 200, contentType: 'application/json',
+      body: JSON.stringify({
+        checkoutSessionId: 'chk_e2e_idempotent',
+        lines: [{ offerId: String(FAKE_ITEM.itemID), qty: 1, unitPrice: { amountMinor: 50000, currency: 'RUB' }, lineTotal: { amountMinor: 50000, currency: 'RUB' }, priceSnapshotId: 'snap_e2e' }],
+        subtotal: { amountMinor: 50000, currency: 'RUB' }, discount: { amountMinor: 0, currency: 'RUB' },
+        delivery: { amountMinor: 0, currency: 'RUB' }, total: { amountMinor: 50000, currency: 'RUB' },
+        fxQuoteId: 'fxq_e2e', expiresAt: new Date(Date.now() + 300000).toISOString(),
+      }),
+    });
+  });
+  await page.route('**/api/v2/storefront/payments/intents', route =>
+    route.fulfill({ status: 200, contentType: 'application/json', body: JSON.stringify({ qrId: 'qr_e2e', nspkurl: 'https://example.com/pay', qrTTL: 5 }) }),
+  );
+
+  await page.goto('/cart');
+  await page.waitForLoadState('networkidle');
+
+  // No <label for="terms-checkbox"> exists in the markup - the checkbox and
+  // its text share a plain clickable wrapper - so toggle the input directly.
+  await page.locator('#terms-checkbox').dispatchEvent('click');
+  await expect(page.locator('#terms-checkbox')).toBeChecked();
+
+  const qrButton = page.getByRole('button', { name: /qr/i }).first();
+  await expect(qrButton).toBeEnabled({ timeout: 10_000 });
+  await qrButton.dblclick();
+
+  // Give the deliberately slow mock time to resolve and for any second,
+  // erroneously-fired request to have landed.
+  await page.waitForTimeout(1000);
+
+  expect(checkoutRequestCount, 'a double-click must not create two checkout sessions').toBe(1);
+});
diff --git a/src/app/pages/cart/cart.component.ts b/src/app/pages/cart/cart.component.ts
index 340f411..a72798f 100644
--- a/src/app/pages/cart/cart.component.ts
+++ b/src/app/pages/cart/cart.component.ts
@@ -189,13 +189,30 @@ export class CartComponent implements OnDestroy {
   convertTotal(amountInBaseCurrency: number): number {
     return this.currencyRates.convert(amountInBaseCurrency, this.currencyRates.baseCurrency, this.currentCurrency);
   }
-  get isCheckoutDisabled(): boolean { return !this.termsAccepted || !this.isAuthenticated() || !this.allRequiredDeliveriesSelected(); }
+  /**
+   * A double-click (or any rapid repeat click) on the checkout button fires
+   * two synchronous handler calls before showPaymentPopup's change detection
+   * has a chance to cover the button - found via E2E
+   * (checkout-idempotent-click.spec.ts), which caught two real
+   * POST /api/v2/storefront/checkout requests from one double-click.
+   * checkoutInFlight closes that window: it is set before anything async
+   * happens, so the second call sees it and bails immediately.
+   */
+  private readonly checkoutInFlight = signal(false);
+
+  get isCheckoutDisabled(): boolean {
+    return !this.termsAccepted || !this.isAuthenticated() || !this.allRequiredDeliveriesSelected() || this.checkoutInFlight();
+  }
 
   selectDelivery(itemID: number, selectedDelivery: DeliveryOption | null): void {
     this.cartService.setSelectedDelivery(itemID, selectedDelivery);
   }
 
   checkout(paymentMethod: PaymentMethod): void {
+    if (this.checkoutInFlight()) {
+      return;
+    }
+
     if (!this.allRequiredDeliveriesSelected()) {
       this.notifications.show(this.i18n.t('cart.deliveryRequired'), 'warning');
       return;
@@ -205,6 +222,8 @@ export class CartComponent implements OnDestroy {
       this.notifications.show(this.i18n.t('cart.acceptTerms'), 'warning');
       return;
     }
+
+    this.checkoutInFlight.set(true);
     this.analytics.track('checkout_started', { itemCount: this.items().length });
     this.openPaymentPopup(paymentMethod);
   }
@@ -248,6 +267,9 @@ export class CartComponent implements OnDestroy {
       clearTimeout(this.closeTimeout);
       this.closeTimeout = undefined;
     }
+    // Every retry/close path routes through here - release the checkout
+    // button so a shopper who dismisses an error can actually try again.
+    this.checkoutInFlight.set(false);
   }
 
   retryPayment(): void {
@@ -446,6 +468,10 @@ export class CartComponent implements OnDestroy {
       clearTimeout(this.closeTimeout);
       this.closeTimeout = undefined;
     }
+    // The popup may stay open to show the error rather than closing, so
+    // this can't rely on closePaymentPopup() being called - release the
+    // checkout button here too, or a failed attempt locks retry out forever.
+    this.checkoutInFlight.set(false);
   }
 
   /**