Independent/extra files

I want to add a php based app that is independent from the WordPress site.
The app has been placed in site/web because it seems to be quite fitting for it and the app directory is .gitignored.
The trellis/bedrock deployments swap out the current release with a new cloned one (except some shared files and folders), the app would be probably removed.

The app has its own development/deployment cycle (it changes only very rarely) hence I don’t think it is a good idea deploying it together with the WordPress site using in a Trellis hook.