diff --git a/src/DTO/SyncConfirmation.php b/src/DTO/SyncConfirmation.php
new file mode 100644
index 0000000..87b8606
--- /dev/null
+++ b/src/DTO/SyncConfirmation.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\DTO;
+
+class SyncConfirmation
+{
+    public function __construct(
+        public readonly bool $confirmDeletions = false,
+        public readonly bool $confirmTypeChanges = false,
+    ) {}
+}
diff --git a/src/DTO/SyncExecutionResult.php b/src/DTO/SyncExecutionResult.php
new file mode 100644
index 0000000..d0cfdb0
--- /dev/null
+++ b/src/DTO/SyncExecutionResult.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\DTO;
+
+use JsonSerializable;
+
+class SyncExecutionResult implements JsonSerializable
+{
+    public function __construct(
+        public readonly int $itemsUpdated,
+        public readonly array $additions = [],
+        public readonly array $deletions = [],
+        public readonly array $modifications = [],
+    ) {}
+
+    public function jsonSerialize(): array
+    {
+        return [
+            'itemsUpdated'  => $this->itemsUpdated,
+            'additions'     => $this->additions,
+            'deletions'     => $this->deletions,
+            'modifications' => $this->modifications,
+        ];
+    }
+}
diff --git a/src/DTO/SyncPreviewResult.php b/src/DTO/SyncPreviewResult.php
new file mode 100644
index 0000000..62bd20e
--- /dev/null
+++ b/src/DTO/SyncPreviewResult.php
@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\DTO;
+
+use JsonSerializable;
+
+class SyncPreviewResult implements JsonSerializable
+{
+    public function __construct(
+        public readonly string $modelTypeId,
+        public readonly string $category,
+        public readonly int $itemCount,
+        public readonly array $additions = [],
+        public readonly array $deletions = [],
+        public readonly array $modifications = [],
+    ) {}
+
+    public function hasImpact(): bool
+    {
+        return array_sum($this->additions) > 0
+            || array_sum($this->deletions) > 0
+            || array_sum($this->modifications) > 0;
+    }
+
+    public function jsonSerialize(): array
+    {
+        return [
+            'modelTypeId'   => $this->modelTypeId,
+            'category'      => $this->category,
+            'itemCount'     => $this->itemCount,
+            'additions'     => $this->additions,
+            'deletions'     => $this->deletions,
+            'modifications' => $this->modifications,
+        ];
+    }
+}
diff --git a/src/Service/Sync/SyncStrategyInterface.php b/src/Service/Sync/SyncStrategyInterface.php
new file mode 100644
index 0000000..18f6ae6
--- /dev/null
+++ b/src/Service/Sync/SyncStrategyInterface.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Service\Sync;
+
+use App\DTO\SyncConfirmation;
+use App\DTO\SyncExecutionResult;
+use App\DTO\SyncPreviewResult;
+use App\Entity\ModelType;
+
+interface SyncStrategyInterface
+{
+    public function supports(ModelType $modelType): bool;
+
+    /**
+     * Compute diff between proposed structure and current items' slots.
+     * Does NOT persist anything.
+     */
+    public function preview(ModelType $modelType, array $newStructure): SyncPreviewResult;
+
+    /**
+     * Apply sync: compare current skeleton requirements (already persisted)
+     * with items' slots and add/remove as needed.
+     */
+    public function execute(ModelType $modelType, SyncConfirmation $confirmation): SyncExecutionResult;
+}