CI Wiz generated a blank or broken page — where do I start debugging?

A blank page in CI4 almost always means an exception is being swallowed silently. Run through this checklist: 1. Confirm `CI_ENVIRONMENT = development` in your `.env` — production mode suppresses all errors. 2. Check `writable/logs/` for a log file with today's date. CI4 writes exceptions there even when they are not displayed. 3. Confirm your virtual host points to the `/public` directory, not the project root. 4. Run `composer install` if you have not already — missing vendor files cause silent failures. 5. Check that the `.env` database credentials are correct and the database exists. 6. If Shield is enabled, run `php spark migrate` — missing auth tables cause a 500 on any authenticated route. 7. Check your web server error log (nginx error.log or Apache error_log) for PHP-level fatal errors that CI4 itself cannot catch.