Use when building or maintaining a Ruby on Rails app — models, controllers, views, routes and migrations; ActiveRecord associations, scopes and query performance; Hotwire (Turbo and Stimulus) UI; Active Job or Solid Queue background work; and Rails tests. Covers N+1 queries, migration safety on live tables, and flaky system tests around Turbo Frames. NOT plain Ruby scripts, gems or CLIs with no Rails loaded (that is `ruby`).
