hook_alterWorkflowMessage - Similar to hook_alterMailParams, but the message is represented as an object

alterWorkflowMessage.diff

diff --git a/CRM/Core/BAO/MessageTemplate.php b/CRM/Core/BAO/MessageTemplate.php
index ab0f8e7b6e..8357047a1b 100644
--- a/CRM/Core/BAO/MessageTemplate.php
+++ b/CRM/Core/BAO/MessageTemplate.php
@@ -351,10 +351,11 @@ class CRM_Core_BAO_MessageTemplate extends CRM_Core_DAO_MessageTemplate implemen
 
     // Allow WorkflowMessage to run any filters/mappings/cleanups.
     $model = $params['model'] ?? WorkflowMessage::create($params['workflow'] ?? 'UNKNOWN');
-    $params = WorkflowMessage::exportAll(WorkflowMessage::importAll($model, $params));
+    WorkflowMessage::importAll($model, $params);
+    CRM_Utils_Hook::alterWorkflowMessage($params['workflow'] ?? 'UNKNOWN', $model);
+    $params = WorkflowMessage::exportAll($model);
     unset($params['model']);
     // Subsequent hooks use $params. Retaining the $params['model'] might be nice - but don't do it unless you figure out how to ensure data-consistency (eg $params['tplParams'] <=> $params['model']).
-    // If you want to expose the model via hook, consider interjecting a new Hook::alterWorkflowMessage($model) between `importAll()` and `exportAll()`.
 
     $sync();
     $params = array_merge($modelDefaults, $viewDefaults, $envelopeDefaults, $params);
diff --git a/CRM/Utils/Hook.php b/CRM/Utils/Hook.php
index a9679480a0..95395bb2ad 100644
--- a/CRM/Utils/Hook.php
+++ b/CRM/Utils/Hook.php
@@ -1219,6 +1219,21 @@ abstract class CRM_Utils_Hook {
     );
   }
 
+  /**
+   * This is hook is called when an automated workflow message is being composed.
+   *
+   * @param string $name
+   * @param \Civi\WorkflowMessage\WorkflowMessageInterface $model
+   *
+   * @return mixed
+   */
+  public static function alterWorkflowMessage(string $name, \Civi\WorkflowMessage\WorkflowMessageInterface $model) {
+    return self::singleton()->invoke(['name', 'model'], $name, $model,
+      self::$_nullObject, self::$_nullObject, self::$_nullObject, self::$_nullObject,
+      'civicrm_alterWorkflowMessage'
+    );
+  }
+
   /**
    * This hook is called when loading a mail-store (e.g. IMAP, POP3, or Maildir).
    *
diff --git a/Civi/Core/Container.php b/Civi/Core/Container.php
index a6e6d555af..1b8a03d044 100644
--- a/Civi/Core/Container.php
+++ b/Civi/Core/Container.php
@@ -443,6 +443,7 @@ class Container {
       'CRM_Core_LegacyErrorHandler',
       'handleException',
     ], -200);
+    $dispatcher->addListener('hook_civicrm_alterWorkflowMessage', $aliasEvent('hook_civicrm_alterWorkflowMessage', 'name'), 100);
     $dispatcher->addListener('civi.actionSchedule.getMappings', ['CRM_Activity_ActionMapping', 'onRegisterActionMappings']);
     $dispatcher->addListener('civi.actionSchedule.getMappings', ['CRM_Contact_ActionMapping', 'onRegisterActionMappings']);
     $dispatcher->addListener('civi.actionSchedule.getMappings', ['CRM_Contribute_ActionMapping_ByPage', 'onRegisterActionMappings']);

index.md

Example

function mymodule_civicrm_alterWorkflowMessage(string $name, $model) {
  // Whenever there's an offline event registration, send BCC email. Get email addr from a custom-field.
  if ($name === 'event_offline_receipt') {
    /** @var \CRM_Event_WorkflowMessage_OfflineReceipt $model */
    $customNotificationList = CustomValue::get('MyEventNotification')
      ->addWhere('entity_id', '=', $model->getEventId())
      ->addSelect('email')
      ->execute();
    foreach ($customNotificationList as $customNotification) {
      $model->addBcc(['email' => $customNotification['email']]);
    }
  }
}

Question

Are there any examples of things in $params that should be accessible in $model but are not?