R0.3: Newsletter-Sync-Binding config-aware + ehrliche Test-Sync-Meldung

Bisher wurde der NullNewsletterSyncClient unbedingt gebunden -
NEWSLETTER_SYNC_ENABLED=true mit echtem Provider haette stumm nichts
getan. Jetzt: Platzhalter-Provider -> No-Op-Client, aktivierter aber
nicht implementierter Provider -> RuntimeException (fail fast). Das
Admin-UI weist beim Test-Sync auf den Platzhalter hin.

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

app/Providers/AppServiceProvider.php

@@ -44,7 +44,20 @@ class AppServiceProvider extends ServiceProvider
      */
     public function register(): void
     {
-        $this->app->bind(NewsletterSyncClient::class, NullNewsletterSyncClient::class);
+        $this->app->bind(NewsletterSyncClient::class, function (): NewsletterSyncClient {
+            $provider = (string) config('newsletter.sync.provider', 'placeholder');
+
+            // Es existiert bislang nur der No-Op-Client. Ein aktivierter, aber
+            // nicht implementierter Provider soll laut schlagen statt stumm
+            // ins Leere zu synchronisieren.
+            if (config('newsletter.sync.enabled') && $provider !== 'placeholder') {
+                throw new \RuntimeException(
+                    "Newsletter-Sync-Provider [{$provider}] ist nicht implementiert – es existiert nur der Platzhalter-Client."
+                );
+            }
+
+            return new NullNewsletterSyncClient;
+        });
         $this->app->singleton(PressReleaseService::class);
         $this->app->singleton(AdminRequestPerformanceMetrics::class);
     }

resources/views/livewire/admin/newsletter/sync.blade.php

@@ -47,6 +47,10 @@ new #[Layout('components.layouts.app'), Title('Newsletter Sync')] class extends
             : 'unsubscribe';
 
         $this->syncMessage = "Test-Sync ausgefuehrt ({$action}) fuer Subscription #{$subscription->id}.";
+
+        if ((string) config('newsletter.sync.provider') === 'placeholder') {
+            $this->syncMessage .= ' Hinweis: Platzhalter-Provider – es wurde kein externes System aufgerufen.';
+        }
     }
 
     public function with(): array

tests/Feature/NewsletterSyncBindingTest.php

@@ -0,0 +1,26 @@
+<?php
+
+use App\Contracts\NewsletterSyncClient;
+use App\Services\Newsletter\NullNewsletterSyncClient;
+
+test('newsletter sync resolves to the null client while no real provider exists', function () {
+    config()->set('newsletter.sync.enabled', false);
+    config()->set('newsletter.sync.provider', 'placeholder');
+
+    expect(app(NewsletterSyncClient::class))->toBeInstanceOf(NullNewsletterSyncClient::class);
+});
+
+test('newsletter sync resolves to the null client for the placeholder provider even when enabled', function () {
+    config()->set('newsletter.sync.enabled', true);
+    config()->set('newsletter.sync.provider', 'placeholder');
+
+    expect(app(NewsletterSyncClient::class))->toBeInstanceOf(NullNewsletterSyncClient::class);
+});
+
+test('an enabled but unimplemented sync provider fails fast instead of silently doing nothing', function () {
+    config()->set('newsletter.sync.enabled', true);
+    config()->set('newsletter.sync.provider', 'mailchimp');
+
+    expect(fn () => app(NewsletterSyncClient::class))
+        ->toThrow(RuntimeException::class, 'mailchimp');
+});