Watch out for this one deprecation warning when upgrading from Rails 7.1 to 7.2 on Heroku

Rails 7.2 deprecates `Rails.application.secrets` in favor of `Rails.application.credentials`, but migrating on Heroku can cause silent failures. When removing the SECRET_KEY_BASE environment variable, Heroku's buildpack automatically regenerates it with a random value, invalidating all existing cookies and breaking external integrations. The solution is to keep SECRET_KEY_BASE in both Rails credentials and Heroku config variables to avoid this silent error.