Ruby gem by Shopify used to enforce modular-monolith boundaries inside a Rails application. Essentially a linter: it defines packages with public/private APIs and flags violations when code from one package reaches into another's privates. Great for static checks, but an audience member at Chikahiro's talk points out it can't catch dynamic Ruby object-to-object calls (e.g. `has_many`/`belongs_to` traversals across packages); one proposed workaround is dynamically extending active-record methods like save/update in test mode to reject cross-domain writes that bypass a public service API.