Turbo frame will be in the request headers
If a request was made with a data-turbo-frame attribute, there will be a header turbo-frame with the same value:
<a data-turbo-frame="my-container" href="/promo">Click here</a>
There will be a header attached to the fetch request:
class Controller
def promo
puts request.headers["turbo-frame"]
# => "my-container"
end
end