diff --git a/apps/symfony/config/services.yaml b/apps/symfony/config/services.yaml
index f8e1b14..bcc6835 100644
--- a/apps/symfony/config/services.yaml
+++ b/apps/symfony/config/services.yaml
@@ -10,6 +10,9 @@ services:
     MiniShop\Shared\Technical\Clock:
         alias: MiniShop\Shared\Technical\SystemClock
 
+    MiniShop\Shared\Technical\IdempotencyStore:
+        alias: MiniShop\Shared\Technical\InMemoryIdempotencyStore
+
     # --- Sales ---
     MiniShop\Sales\Application\:
         resource: '%kernel.project_dir%/src/Sales/Application/'
diff --git a/contracts/sales/v1/Event/OrderCancelled.php b/contracts/sales/v1/Event/OrderCancelled.php
index 34bbb8d..748ca52 100644
--- a/contracts/sales/v1/Event/OrderCancelled.php
+++ b/contracts/sales/v1/Event/OrderCancelled.php
@@ -12,5 +12,6 @@ final readonly class OrderCancelled
 {
     public function __construct(
         public string $orderId,
+        public string $correlationId = '',
     ) {}
 }
diff --git a/contracts/sales/v1/Event/OrderConfirmed.php b/contracts/sales/v1/Event/OrderConfirmed.php
index b2fb2f9..a647273 100644
--- a/contracts/sales/v1/Event/OrderConfirmed.php
+++ b/contracts/sales/v1/Event/OrderConfirmed.php
@@ -19,5 +19,6 @@ final readonly class OrderConfirmed
         public int $totalInCents,
         public string $currency,
         public array $lines,
+        public string $correlationId = '',
     ) {}
 }
diff --git a/contracts/sales/v1/Event/OrderPlaced.php b/contracts/sales/v1/Event/OrderPlaced.php
index bb706d2..ff6ef75 100644
--- a/contracts/sales/v1/Event/OrderPlaced.php
+++ b/contracts/sales/v1/Event/OrderPlaced.php
@@ -20,5 +20,6 @@ final readonly class OrderPlaced
         public string $currency,
         public string $placedAt,
         public array $lines,
+        public string $correlationId = '',
     ) {}
 }
diff --git a/src/Invoicing/Interfaces/Messaging/WhenOrderConfirmed.php b/src/Invoicing/Interfaces/Messaging/WhenOrderConfirmed.php
index 6fd1ab5..b157ac3 100644
--- a/src/Invoicing/Interfaces/Messaging/WhenOrderConfirmed.php
+++ b/src/Invoicing/Interfaces/Messaging/WhenOrderConfirmed.php
@@ -7,21 +7,42 @@ namespace MiniShop\Invoicing\Interfaces\Messaging;
 use MiniShop\Contracts\Sales\V1\Event\OrderConfirmed;
 use MiniShop\Invoicing\Application\Command\IssueInvoiceForExternalOrder;
 use MiniShop\Invoicing\Application\Command\IssueInvoiceForExternalOrderHandler;
+use MiniShop\Shared\Technical\IdempotencyStore;
+use Psr\Log\LoggerInterface;
+use Psr\Log\NullLogger;
 use Symfony\Component\Messenger\Attribute\AsMessageHandler;
 
 /**
- * Conformist : Invoicing consomme le contrat sales.v1.OrderConfirmed tel quel,
- * sans traduction. La dependance upstream est explicite.
+ * Conformist + Idempotent : consomme sales.v1.OrderConfirmed tel quel.
+ * Garde d'idempotence pour eviter les doublons en cas de re-delivery.
  */
 #[AsMessageHandler]
 final readonly class WhenOrderConfirmed
 {
     public function __construct(
         private IssueInvoiceForExternalOrderHandler $handler,
+        private IdempotencyStore $idempotencyStore,
+        private LoggerInterface $logger = new NullLogger(),
     ) {}
 
     public function __invoke(OrderConfirmed $message): void
     {
+        $idempotencyKey = 'invoicing:order-confirmed:' . $message->orderId;
+
+        if ($this->idempotencyStore->isDuplicate($idempotencyKey)) {
+            $this->logger->info('Duplicate OrderConfirmed ignored.', [
+                'orderId' => $message->orderId,
+                'correlationId' => $message->correlationId,
+            ]);
+
+            return;
+        }
+
+        $this->logger->info('Processing OrderConfirmed.', [
+            'orderId' => $message->orderId,
+            'correlationId' => $message->correlationId,
+        ]);
+
         ($this->handler)(new IssueInvoiceForExternalOrder(
             externalOrderId: $message->orderId,
             customerName: 'Customer ' . $message->customerId,
diff --git a/src/LegacyFulfillment/Interfaces/Messaging/WhenOrderConfirmed.php b/src/LegacyFulfillment/Interfaces/Messaging/WhenOrderConfirmed.php
index 5ecaf0a..479e9ca 100644
--- a/src/LegacyFulfillment/Interfaces/Messaging/WhenOrderConfirmed.php
+++ b/src/LegacyFulfillment/Interfaces/Messaging/WhenOrderConfirmed.php
@@ -8,11 +8,14 @@ use MiniShop\Contracts\Sales\V1\Event\OrderConfirmed;
 use MiniShop\LegacyFulfillment\Application\Command\RequestShipmentFromSalesOrder;
 use MiniShop\LegacyFulfillment\Application\Command\RequestShipmentFromSalesOrderHandler;
 use MiniShop\LegacyFulfillment\Infrastructure\AntiCorruption\LegacyShipmentAcl;
+use MiniShop\Shared\Technical\IdempotencyStore;
+use Psr\Log\LoggerInterface;
+use Psr\Log\NullLogger;
 use Symfony\Component\Messenger\Attribute\AsMessageHandler;
 
 /**
- * Consumer ACL : recoit sales.v1.OrderConfirmed, passe par l'Anti-Corruption Layer
- * pour traduire vers le modele legacy, puis delegue au handler applicatif.
+ * Consumer ACL + Idempotent : passe par l'Anti-Corruption Layer avec
+ * garde d'idempotence pour eviter les doublons.
  */
 #[AsMessageHandler]
 final readonly class WhenOrderConfirmed
@@ -20,10 +23,28 @@ final readonly class WhenOrderConfirmed
     public function __construct(
         private LegacyShipmentAcl $acl,
         private RequestShipmentFromSalesOrderHandler $handler,
+        private IdempotencyStore $idempotencyStore,
+        private LoggerInterface $logger = new NullLogger(),
     ) {}
 
     public function __invoke(OrderConfirmed $message): void
     {
+        $idempotencyKey = 'fulfillment:order-confirmed:' . $message->orderId;
+
+        if ($this->idempotencyStore->isDuplicate($idempotencyKey)) {
+            $this->logger->info('Duplicate OrderConfirmed ignored.', [
+                'orderId' => $message->orderId,
+                'correlationId' => $message->correlationId,
+            ]);
+
+            return;
+        }
+
+        $this->logger->info('Processing OrderConfirmed via ACL.', [
+            'orderId' => $message->orderId,
+            'correlationId' => $message->correlationId,
+        ]);
+
         $legacyCommand = $this->acl->fromSalesOrderConfirmed($message);
 
         ($this->handler)(new RequestShipmentFromSalesOrder(
diff --git a/src/Sales/Infrastructure/Messaging/MessengerSalesEventPublisher.php b/src/Sales/Infrastructure/Messaging/MessengerSalesEventPublisher.php
index df38de2..ebbb135 100644
--- a/src/Sales/Infrastructure/Messaging/MessengerSalesEventPublisher.php
+++ b/src/Sales/Infrastructure/Messaging/MessengerSalesEventPublisher.php
@@ -12,11 +12,12 @@ use MiniShop\Sales\Domain\Event\OrderCancelled;
 use MiniShop\Sales\Domain\Event\OrderConfirmed;
 use MiniShop\Sales\Domain\Event\OrderPlaced;
 use MiniShop\Sales\Domain\Model\OrderLine;
+use MiniShop\Shared\Technical\CorrelationId;
 use Symfony\Component\Messenger\MessageBusInterface;
 
 /**
  * Publie les evenements de domaine Sales sous forme de contrats Published Language
- * via Symfony Messenger. Remplace le NaiveSalesEventPublisher.
+ * via Symfony Messenger. Propage un correlationId pour le tracing.
  */
 final readonly class MessengerSalesEventPublisher implements SalesEventPublisher
 {
@@ -33,6 +34,7 @@ final readonly class MessengerSalesEventPublisher implements SalesEventPublisher
             currency: $event->total->currency,
             placedAt: $event->placedAt->format(\DateTimeInterface::ATOM),
             lines: [],
+            correlationId: CorrelationId::generate()->toString(),
         ));
     }
 
@@ -52,6 +54,7 @@ final readonly class MessengerSalesEventPublisher implements SalesEventPublisher
                 ],
                 $event->lines,
             ),
+            correlationId: CorrelationId::generate()->toString(),
         ));
     }
 
@@ -59,6 +62,7 @@ final readonly class MessengerSalesEventPublisher implements SalesEventPublisher
     {
         $this->messageBus->dispatch(new OrderCancelledContract(
             orderId: $event->orderId->toString(),
+            correlationId: CorrelationId::generate()->toString(),
         ));
     }
 }
diff --git a/src/Shared/Technical/CorrelationId.php b/src/Shared/Technical/CorrelationId.php
new file mode 100644
index 0000000..a13efb2
--- /dev/null
+++ b/src/Shared/Technical/CorrelationId.php
@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MiniShop\Shared\Technical;
+
+final readonly class CorrelationId
+{
+    private function __construct(public string $value) {}
+
+    public static function generate(): self
+    {
+        return new self(UuidGenerator::generate());
+    }
+
+    public static function fromString(string $value): self
+    {
+        return new self($value);
+    }
+
+    public function toString(): string
+    {
+        return $this->value;
+    }
+}
diff --git a/src/Shared/Technical/IdempotencyStore.php b/src/Shared/Technical/IdempotencyStore.php
new file mode 100644
index 0000000..2943f35
--- /dev/null
+++ b/src/Shared/Technical/IdempotencyStore.php
@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MiniShop\Shared\Technical;
+
+interface IdempotencyStore
+{
+    /**
+     * Returns true if the key was already processed (duplicate).
+     * Returns false and marks the key as processed (first time).
+     */
+    public function isDuplicate(string $key): bool;
+}
diff --git a/src/Shared/Technical/InMemoryIdempotencyStore.php b/src/Shared/Technical/InMemoryIdempotencyStore.php
new file mode 100644
index 0000000..14da900
--- /dev/null
+++ b/src/Shared/Technical/InMemoryIdempotencyStore.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MiniShop\Shared\Technical;
+
+final class InMemoryIdempotencyStore implements IdempotencyStore
+{
+    /** @var array<string, true> */
+    private array $processed = [];
+
+    public function isDuplicate(string $key): bool
+    {
+        if (isset($this->processed[$key])) {
+            return true;
+        }
+
+        $this->processed[$key] = true;
+
+        return false;
+    }
+}
diff --git a/tests/Contract/Sales/v1/ConformistCompatibilityTest.php b/tests/Contract/Sales/v1/ConformistCompatibilityTest.php
index 79306bc..7dc3200 100644
--- a/tests/Contract/Sales/v1/ConformistCompatibilityTest.php
+++ b/tests/Contract/Sales/v1/ConformistCompatibilityTest.php
@@ -10,6 +10,7 @@ use MiniShop\Invoicing\Application\Command\IssueInvoiceForExternalOrderHandler;
 use MiniShop\Invoicing\Infrastructure\Persistence\InMemoryInvoiceRepository;
 use MiniShop\Invoicing\Infrastructure\SequentialInvoiceNumberGenerator;
 use MiniShop\Invoicing\Interfaces\Messaging\WhenOrderConfirmed;
+use MiniShop\Shared\Technical\InMemoryIdempotencyStore;
 use MiniShop\Shared\Technical\SystemClock;
 use PHPUnit\Framework\TestCase;
 
@@ -28,7 +29,7 @@ final class ConformistCompatibilityTest extends TestCase
             new SequentialInvoiceNumberGenerator(),
             new SystemClock(),
         );
-        $consumer = new WhenOrderConfirmed($handler);
+        $consumer = new WhenOrderConfirmed($handler, new InMemoryIdempotencyStore());
 
         $message = new OrderConfirmed(
             orderId: 'order-conformist-001',
diff --git a/tests/Integration/IdempotentConsumerTest.php b/tests/Integration/IdempotentConsumerTest.php
new file mode 100644
index 0000000..e8cbda1
--- /dev/null
+++ b/tests/Integration/IdempotentConsumerTest.php
@@ -0,0 +1,97 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MiniShop\Tests\Integration;
+
+use MiniShop\Contracts\Sales\V1\Event\OrderConfirmed;
+use MiniShop\Invoicing\Application\Command\IssueInvoiceForExternalOrderHandler;
+use MiniShop\Invoicing\Infrastructure\Persistence\InMemoryInvoiceRepository;
+use MiniShop\Invoicing\Infrastructure\SequentialInvoiceNumberGenerator;
+use MiniShop\Invoicing\Interfaces\Messaging\WhenOrderConfirmed as InvoicingConsumer;
+use MiniShop\LegacyFulfillment\Application\Command\RequestShipmentFromSalesOrderHandler;
+use MiniShop\LegacyFulfillment\Infrastructure\AntiCorruption\LegacyShipmentAcl;
+use MiniShop\LegacyFulfillment\Infrastructure\Gateway\FakeLegacyFulfillmentGateway;
+use MiniShop\LegacyFulfillment\Infrastructure\Persistence\InMemoryShipmentRequestRepository;
+use MiniShop\LegacyFulfillment\Interfaces\Messaging\WhenOrderConfirmed as FulfillmentConsumer;
+use MiniShop\Shared\Technical\InMemoryIdempotencyStore;
+use MiniShop\Shared\Technical\SystemClock;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Test d'idempotence : un message recu deux fois ne doit pas creer de doublon.
+ */
+final class IdempotentConsumerTest extends TestCase
+{
+    public function test_invoicing_consumer_ignores_duplicate(): void
+    {
+        $invoiceRepo = new InMemoryInvoiceRepository();
+        $idempotencyStore = new InMemoryIdempotencyStore();
+
+        $consumer = new InvoicingConsumer(
+            new IssueInvoiceForExternalOrderHandler(
+                $invoiceRepo,
+                new SequentialInvoiceNumberGenerator(),
+                new SystemClock(),
+            ),
+            $idempotencyStore,
+        );
+
+        $message = $this->createMessage('idem-001');
+
+        $consumer($message);
+        $consumer($message); // duplicate
+
+        // Only one invoice should exist
+        $invoice = $invoiceRepo->findByExternalOrderId('idem-001');
+        self::assertNotNull($invoice);
+        self::assertSame('INV-000001', $invoice->invoiceNumber);
+    }
+
+    public function test_fulfillment_consumer_ignores_duplicate(): void
+    {
+        $shipmentRepo = new InMemoryShipmentRequestRepository();
+        $gateway = new FakeLegacyFulfillmentGateway();
+        $idempotencyStore = new InMemoryIdempotencyStore();
+
+        $consumer = new FulfillmentConsumer(
+            new LegacyShipmentAcl(),
+            new RequestShipmentFromSalesOrderHandler($shipmentRepo, $gateway, new SystemClock()),
+            $idempotencyStore,
+        );
+
+        $message = $this->createMessage('idem-002');
+
+        $consumer($message);
+        $consumer($message); // duplicate
+
+        // Only one shipment should exist, only one gateway call
+        self::assertCount(1, $gateway->sentRequests());
+    }
+
+    public function test_correlation_id_is_propagated(): void
+    {
+        $message = new OrderConfirmed(
+            orderId: 'corr-001',
+            customerId: 'cust-001',
+            totalInCents: 1000,
+            currency: 'EUR',
+            lines: [['productName' => 'X', 'quantity' => 1, 'unitPriceInCents' => 1000, 'currency' => 'EUR']],
+            correlationId: 'corr-id-abc-123',
+        );
+
+        self::assertSame('corr-id-abc-123', $message->correlationId);
+    }
+
+    private function createMessage(string $orderId): OrderConfirmed
+    {
+        return new OrderConfirmed(
+            orderId: $orderId,
+            customerId: 'cust-001',
+            totalInCents: 1500,
+            currency: 'EUR',
+            lines: [['productName' => 'Widget', 'quantity' => 1, 'unitPriceInCents' => 1500, 'currency' => 'EUR']],
+            correlationId: 'test-correlation-id',
+        );
+    }
+}
diff --git a/tests/Integration/InvoicingConformistTest.php b/tests/Integration/InvoicingConformistTest.php
index e0a6dc3..724ffaf 100644
--- a/tests/Integration/InvoicingConformistTest.php
+++ b/tests/Integration/InvoicingConformistTest.php
@@ -9,6 +9,7 @@ use MiniShop\Invoicing\Infrastructure\Persistence\InMemoryInvoiceRepository;
 use MiniShop\Invoicing\Infrastructure\SequentialInvoiceNumberGenerator;
 use MiniShop\Invoicing\Interfaces\Messaging\WhenOrderConfirmed;
 use MiniShop\Invoicing\Application\Command\IssueInvoiceForExternalOrderHandler;
+use MiniShop\Shared\Technical\InMemoryIdempotencyStore;
 use MiniShop\Shared\Technical\SystemClock;
 use PHPUnit\Framework\TestCase;
 
@@ -27,6 +28,7 @@ final class InvoicingConformistTest extends TestCase
                 new SequentialInvoiceNumberGenerator(),
                 new SystemClock(),
             ),
+            new InMemoryIdempotencyStore(),
         );
 
         $consumer(new OrderConfirmed(
diff --git a/tests/Integration/LegacyFulfillmentAclTest.php b/tests/Integration/LegacyFulfillmentAclTest.php
index 015892f..7c2350a 100644
--- a/tests/Integration/LegacyFulfillmentAclTest.php
+++ b/tests/Integration/LegacyFulfillmentAclTest.php
@@ -11,6 +11,7 @@ use MiniShop\LegacyFulfillment\Infrastructure\AntiCorruption\LegacyShipmentAcl;
 use MiniShop\LegacyFulfillment\Infrastructure\Gateway\FakeLegacyFulfillmentGateway;
 use MiniShop\LegacyFulfillment\Infrastructure\Persistence\InMemoryShipmentRequestRepository;
 use MiniShop\LegacyFulfillment\Interfaces\Messaging\WhenOrderConfirmed;
+use MiniShop\Shared\Technical\InMemoryIdempotencyStore;
 use MiniShop\Shared\Technical\SystemClock;
 use PHPUnit\Framework\TestCase;
 
@@ -28,6 +29,7 @@ final class LegacyFulfillmentAclTest extends TestCase
         $consumer = new WhenOrderConfirmed(
             new LegacyShipmentAcl(),
             new RequestShipmentFromSalesOrderHandler($shipmentRepo, $gateway, new SystemClock()),
+            new InMemoryIdempotencyStore(),
         );
 
         $consumer(new OrderConfirmed(
diff --git a/tests/Unit/Shared/IdempotencyTest.php b/tests/Unit/Shared/IdempotencyTest.php
new file mode 100644
index 0000000..0759259
--- /dev/null
+++ b/tests/Unit/Shared/IdempotencyTest.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MiniShop\Tests\Unit\Shared;
+
+use MiniShop\Shared\Technical\InMemoryIdempotencyStore;
+use PHPUnit\Framework\TestCase;
+
+final class IdempotencyTest extends TestCase
+{
+    public function test_first_call_is_not_duplicate(): void
+    {
+        $store = new InMemoryIdempotencyStore();
+
+        self::assertFalse($store->isDuplicate('key-1'));
+    }
+
+    public function test_second_call_is_duplicate(): void
+    {
+        $store = new InMemoryIdempotencyStore();
+
+        $store->isDuplicate('key-1');
+
+        self::assertTrue($store->isDuplicate('key-1'));
+    }
+
+    public function test_different_keys_are_independent(): void
+    {
+        $store = new InMemoryIdempotencyStore();
+
+        $store->isDuplicate('key-1');
+
+        self::assertFalse($store->isDuplicate('key-2'));
+    }
+}