diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -2613,6 +2613,7 @@
     'PhabricatorBarePageView' => 'view/page/PhabricatorBarePageView.php',
     'PhabricatorBaseURISetupCheck' => 'applications/config/check/PhabricatorBaseURISetupCheck.php',
     'PhabricatorBcryptPasswordHasher' => 'infrastructure/util/password/PhabricatorBcryptPasswordHasher.php',
+    'PhabricatorBeforeDestructionEngineExtension' => 'applications/system/engine/PhabricatorBeforeDestructionEngineExtension.php',
     'PhabricatorBinariesSetupCheck' => 'applications/config/check/PhabricatorBinariesSetupCheck.php',
     'PhabricatorBitbucketAuthProvider' => 'applications/auth/provider/PhabricatorBitbucketAuthProvider.php',
     'PhabricatorBoardColumnsSearchEngineAttachment' => 'applications/project/engineextension/PhabricatorBoardColumnsSearchEngineAttachment.php',
@@ -8974,6 +8975,7 @@
     'PhabricatorBarePageView' => 'AphrontPageView',
     'PhabricatorBaseURISetupCheck' => 'PhabricatorSetupCheck',
     'PhabricatorBcryptPasswordHasher' => 'PhabricatorPasswordHasher',
+    'PhabricatorBeforeDestructionEngineExtension' => 'Phobject',
     'PhabricatorBinariesSetupCheck' => 'PhabricatorSetupCheck',
     'PhabricatorBitbucketAuthProvider' => 'PhabricatorOAuth1AuthProvider',
     'PhabricatorBoardColumnsSearchEngineAttachment' => 'PhabricatorSearchEngineAttachment',
diff --git a/src/applications/system/engine/PhabricatorBeforeDestructionEngineExtension.php b/src/applications/system/engine/PhabricatorBeforeDestructionEngineExtension.php
new file mode 100644
--- /dev/null
+++ b/src/applications/system/engine/PhabricatorBeforeDestructionEngineExtension.php
@@ -0,0 +1,54 @@
+<?php
+
+/**
+ * Abstract "Before Destruction Engine",
+ * to fire an hook before something is permamently destroyed.
+ */
+abstract class PhabricatorBeforeDestructionEngineExtension extends Phobject {
+
+  /**
+   * Get the extension internal key.
+   *
+   * @return string
+   */
+  final public function getExtensionKey(): string {
+    return $this->getPhobjectClassConstant('EXTENSIONKEY');
+  }
+
+  /**
+   * Get the extension human name.
+   *
+   * @return string
+   */
+  abstract public function getExtensionName(): string;
+
+  /**
+   * Check whenever your extension supports a "Berfore Destruction" hook
+   * on the specified object.
+   */
+  public function canBeforeDestroyObject(
+    PhabricatorDestructionEngine $destruction_engine,
+    $object): bool {
+    return true;
+  }
+
+  /**
+   * Call your "Berfore Destruction" hook on the specified object.
+   * The object is guaranteed to be consistent with canBeforeDestroyObject().
+   */
+  abstract public function beforeDestroyObject(
+    PhabricatorDestructionEngine $engine,
+    $object);
+
+  /**
+   * Get all "Before Destruction Engine" extensions.
+   */
+  final public static function getAllExtensions(): array {
+    $map = new PhutilClassMapQuery();
+    return $map
+      ->setAncestorClass(__CLASS__)
+      ->setUniqueMethod('getExtensionKey')
+      ->execute();
+  }
+
+}
diff --git a/src/applications/system/engine/PhabricatorDestructionEngine.php b/src/applications/system/engine/PhabricatorDestructionEngine.php
--- a/src/applications/system/engine/PhabricatorDestructionEngine.php
+++ b/src/applications/system/engine/PhabricatorDestructionEngine.php
@@ -73,6 +73,17 @@
       }
     }
 
+    if ($object_phid) {
+      // Allow extension to do something before the destruction.
+      $before_extensions =
+        PhabricatorBeforeDestructionEngineExtension::getAllExtensions();
+      foreach ($before_extensions as $key => $before_extension) {
+        if ($before_extension->canBeforeDestroyObject($this, $object)) {
+          $before_extension->beforeDestroyObject($this, $object);
+        }
+      }
+    }
+
     $object->destroyObjectPermanently($this);
 
     if ($object_phid) {