Downgrade-Vorkehrungen: Kontingent-Sperre beim Tarifwechsel, Gutschriften nicht spiegeln

QA-Befund 07.07.: Der Wechsel zurück in einen kleineren Tarif erzeugte
eine Proration-Gutschrift (negative Stripe-Rechnung) — die STR-Spiegelung
crashte an den unsigned-Spalten (Webhook-500), und der Wechsel war trotz
verbrauchtem Monatskontingent möglich.

- ProcessStripeWebhook: Belege ohne positiven Rechnungsbetrag
  (Gutschrift/Null-Rechnung) werden geloggt übersprungen statt gespiegelt
- CheckoutController::swap: Wechsel gesperrt, wenn der Monatsverbrauch
  das Kontingent des Ziel-Tarifs übersteigt (möglich ab Monatserstem)
- Buchungs-Modal: erklärt die Sperre inkl. Datum statt Bestätigungs-
  Button; Proration-Hinweis deckt jetzt auch die Guthaben-Richtung ab

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

tests/Feature/Billing/BookingsPageTest.php

@@ -381,3 +381,28 @@ test('a swap booking for a subscriber on grace period announces the revoked canc
         ->assertSet('booking.resumes_cancellation', true)
         ->assertSee('Ihre vorgemerkte Kündigung wird durch den Wechsel aufgehoben.');
 });
+
+test('a swap to a plan below the current monthly usage is blocked in the modal', function () {
+    /** @var TestCase $this */
+    $user = bookingsTestCustomer();
+    BillingAddress::factory()->create(['user_id' => $user->id]);
+    $user->forceFill(['press_release_quota_used_this_month' => 12])->save();
+
+    $currentPlan = Plan::factory()->create([
+        'stripe_price_id_monthly' => 'price_test_m_quota1',
+        'press_release_quota' => 20,
+    ]);
+    $targetPlan = Plan::factory()->create([
+        'stripe_price_id_monthly' => 'price_test_m_quota2',
+        'press_release_quota' => 5,
+    ]);
+    subscribeUserToPlan($user, $currentPlan);
+
+    $this->actingAs($user);
+
+    LivewireVolt::test('customer.bookings')
+        ->call('selectBooking', 'subscription', $targetPlan->slug, 'monthly')
+        ->assertSet('booking.quota_blocked', true)
+        ->assertSee('Ein Wechsel in diesen Tarif ist erst ab dem')
+        ->assertDontSee('Kostenpflichtig wechseln');
+});

tests/Feature/Billing/CheckoutFlowTest.php

@@ -277,3 +277,54 @@ test('a failing plan swap reports a friendly notice instead of an error page', f
         ->assertRedirect(route('me.bookings.index'))
         ->assertSessionHas('checkout-notice');
 });
+
+test('a plan swap is blocked when the monthly usage exceeds the target quota', function () {
+    /** @var TestCase $this */
+    $user = checkoutTestCustomer();
+    $user->forceFill(['press_release_quota_used_this_month' => 12])->save();
+
+    $currentPlan = Plan::factory()->create([
+        'stripe_price_id_monthly' => 'price_test_m_swap6a',
+        'press_release_quota' => 20,
+    ]);
+    subscribeUserToPlan($user, $currentPlan);
+    $targetPlan = Plan::factory()->create([
+        'stripe_price_id_monthly' => 'price_test_m_swap6b',
+        'press_release_quota' => 5,
+    ]);
+
+    $this->mock(StripeCheckoutService::class, function ($mock) {
+        $mock->shouldNotReceive('swapSubscription');
+    });
+
+    $this->actingAs($user)
+        ->post(route('me.checkout.swap', ['planSlug' => $targetPlan->slug, 'interval' => 'monthly']))
+        ->assertRedirect(route('me.bookings.index'))
+        ->assertSessionHas('checkout-notice');
+});
+
+test('a plan swap is allowed when the monthly usage still fits the target quota', function () {
+    /** @var TestCase $this */
+    $user = checkoutTestCustomer();
+    $user->forceFill(['press_release_quota_used_this_month' => 5])->save();
+
+    $currentPlan = Plan::factory()->create([
+        'stripe_price_id_monthly' => 'price_test_m_swap7a',
+        'press_release_quota' => 20,
+    ]);
+    subscribeUserToPlan($user, $currentPlan);
+    $targetPlan = Plan::factory()->create([
+        'stripe_price_id_monthly' => 'price_test_m_swap7b',
+        'press_release_quota' => 5,
+    ]);
+
+    $this->mock(StripeCheckoutService::class, function ($mock) use ($targetPlan) {
+        $mock->shouldReceive('swapSubscription')
+            ->once()
+            ->withArgs(fn (User $u, Plan $p, string $interval) => $p->is($targetPlan) && $interval === 'monthly');
+    });
+
+    $this->actingAs($user)
+        ->post(route('me.checkout.swap', ['planSlug' => $targetPlan->slug, 'interval' => 'monthly']))
+        ->assertRedirect(route('me.bookings.index', ['checkout' => 'wechsel']));
+});

tests/Feature/Billing/StripeWebhookProcessingTest.php

@@ -160,3 +160,29 @@ test('the listener is wired to the cashier webhook event', function () {
         ProcessStripeWebhook::class,
     );
 });
+
+test('a proration credit with a negative total is skipped without an invoice', function () {
+    // Downgrade-Gutschrift (QA-Befund 07.07.): negative Beträge sprengten
+    // die unsigned-Spalten und beantworteten den Webhook mit 500.
+    $user = User::factory()->create(['stripe_id' => 'cus_test_1']);
+
+    app(ProcessStripeWebhook::class)->handle(new WebhookReceived(stripeInvoicePayload($user, [
+        'subtotal' => -6992,
+        'tax' => -1329,
+        'total' => -8321,
+    ])));
+
+    expect(Invoice::count())->toBe(0);
+});
+
+test('a zero-total stripe invoice is skipped without an invoice', function () {
+    $user = User::factory()->create(['stripe_id' => 'cus_test_1']);
+
+    app(ProcessStripeWebhook::class)->handle(new WebhookReceived(stripeInvoicePayload($user, [
+        'subtotal' => 0,
+        'tax' => 0,
+        'total' => 0,
+    ])));
+
+    expect(Invoice::count())->toBe(0);
+});