Cancel: Guarding State Transitions

A member route for one specific transition

index, show, and create are three of Rails' seven standard RESTful actions — resources :bookings gives you all seven for free, but only: %i[index show create] in routes.rb deliberately keeps only three. Cancelling isn't update (which would let a client PATCH ANY field, including sneaking status: "completed" in through the back door) — it's its own narrow, named route: