How would you design a scalable Drupal architecture? Explain event subscribers vs hooks with use cases. How do you implement idempotent APIs in Drupal? How do you handle large file processing (batch/queue)? Explain revision + moderation + publishing flow. How do you optimize database queries in Drupal? How would you integrate Drupal with external systems (JIRA/Salesforce)? How do you implement webhooks in Drupal? How does cache invalidation with tags work internally?