fix(mail) : stop le spam GlitchTip de sync (reconnexion AUTHENTICATIONFAILED + double-log)

Un seul echec de dossier (empty response) generait 4 events GlitchTip :
- le bloc de detection de suppression rappelait listMessages quand le
  fetch initial avait echoue, forcant une reconnexion IMAP refusee par OVH
  (AUTHENTICATIONFAILED, throttling) ;
- chaque echec etait logge 2x en error (provider + service).

Fix :
- garde `if (null !== $remoteHeaders)` autour de la detection de
  suppression : si le fetch a echoue, on saute le diff (reprise au
  cycle suivant), plus de reconnexion parasite ;
- le log service des MailProviderException passe en warning (le provider
  reste la source unique au niveau error pour GlitchTip, couvre aussi les
  chemins HTTP).

Net : 1 event GlitchTip par echec de dossier.
Test de regression : testSyncFolderDoesNotRefetchMessagesWhenInitialFetchFails.

tests/Unit/Service/MailSyncServiceTest.php

@@ -8,6 +8,7 @@ use App\Module\Mail\Application\Dto\MailFolderDto;
 use App\Module\Mail\Application\Service\MailSyncService;
 use App\Module\Mail\Domain\Entity\MailConfiguration;
 use App\Module\Mail\Domain\Entity\MailFolder;
+use App\Module\Mail\Domain\Exception\MailProviderException;
 use App\Module\Mail\Domain\Provider\MailProviderInterface;
 use App\Module\Mail\Domain\Repository\MailConfigurationRepositoryInterface;
 use App\Module\Mail\Domain\Repository\MailFolderRepositoryInterface;
@@ -237,6 +238,58 @@ class MailSyncServiceTest extends TestCase
         self::assertNotEmpty($report->errors);
     }
 
+    public function testSyncFolderDoesNotRefetchMessagesWhenInitialFetchFails(): void
+    {
+        // Regression: when the message fetch fails, the deletion-detection block
+        // used to re-call listMessages, which forced an IMAP reconnect and tripped
+        // OVH throttling (AUTHENTICATIONFAILED) — turning one folder failure into
+        // several GlitchTip events. listMessages must be called exactly once.
+        $config = new MailConfiguration();
+        $config->setEnabled(true);
+
+        $configRepo = $this->createMock(MailConfigurationRepositoryInterface::class);
+        $configRepo->method('findSingleton')->willReturn($config);
+
+        $folder = new MailFolder();
+        $folder->setPath('INBOX/RH/LUCILE NEAU');
+
+        $messageRepo = $this->createMock(MailMessageRepositoryInterface::class);
+        $messageRepo->method('findMaxUidInFolder')->willReturn(0);
+        $messageRepo->method('findLastNByFolder')->willReturn([]);
+        // The DB still holds messages: without the guard the deletion block would
+        // re-fetch the remote list to diff against these UIDs.
+        $messageRepo->method('findAllUidsByFolder')->willReturn([1, 2, 3]);
+
+        $provider = $this->createMock(MailProviderInterface::class);
+        $provider->expects(self::once())
+            ->method('listMessages')
+            ->willThrowException(
+                MailProviderException::operationFailed('listMessages', 'empty response')
+            )
+        ;
+
+        $folderRepo = $this->createMock(MailFolderRepositoryInterface::class);
+        $em         = $this->createMock(EntityManagerInterface::class);
+        $em->expects(self::never())->method('remove');
+
+        $service = new MailSyncService(
+            provider: $provider,
+            configRepository: $configRepo,
+            folderRepository: $folderRepo,
+            messageRepository: $messageRepo,
+            entityManager: $em,
+            lockFactory: $this->makeLockFactory(),
+            logger: new NullLogger(),
+            managerRegistry: $this->createMock(ManagerRegistry::class),
+        );
+
+        $report = $service->syncFolder($folder);
+
+        // Exactly one error recorded (the fetch failure), not a cascade.
+        self::assertCount(1, $report->errors);
+        self::assertSame(0, $report->deletedCount);
+    }
+
     private function makeLockFactory(bool $acquired = true): LockFactory
     {
         $lock = $this->createMock(SharedLockInterface::class);