Bugsnag Recipe

require 'contrib/bugsnag.php';

Configuration

bugsnag_api_key – the API Key associated with the project. Informs Bugsnag which project has been deployed. This is the only required field.
bugsnag_provider – the name of your source control provider. Required when repository is supplied and only for on-premise services.
bugsnag_app_version – the app version of the code you are currently deploying. Only set this if you tag your releases with semantic version numbers and deploy infrequently. (Optional.)

Since you should only notify Bugsnag of a successful deployment, the bugsnag:notify task should be executed right at the end.

after('deploy', 'bugsnag:notify');

Notifies Bugsnag of deployment.