**Motivation** We have created a module called [push_framework_templates](https://www.drupal.org/project/push_framework_templates) that customizes notification text based on the channel and the notification being sent. To do its job, it needs to know what triggered the notification / which source plugin fired it and what the source object ID is. Without this patch, the ChannelPrepareTemplates event carries no information about the trigger, so push_framework_templates has no way to select the right template. This patch exposes that context. **Suggested change** Add $plugin and $oid as optional constructor parameters to ChannelPrepareTemplates (backward-compatible, both nullable with NULL defaults) and pass them from ChannelBase::prepareTemplates(). MR will be provided.