Keep a String error message's status when the route names a failure entity

[ericproulx]

Summary

ErrorFormatter::Base#present applies the entity that a route's failure codes name for the response status to whatever error! was given. An entity that exposes attributes can't read any off a String, so this raises while rendering and the failsafe answers 500 in place of the requested status:

desc 'Get a thing', failure: [[401, 'Unauthorized', API::Error]]
get '/thing' do
  error!('Unauthorized', 401) # => 500 Internal Server Error
end

The failure block method and the http_codes: keyword have always behaved this way. #2949 (unreleased) made the failure: keyword present too, which is the spelling grape-swagger's README recommends (failure: [[401, 'KittenBitesError', Entities::BadKitten]]). So on master, an API that documents its 401 that way and calls error! with a String now gets a 500 for every 401. 4.0.1 answered 401.

The failure entities document a structured error body, and every README example passes a Hash to error!. A String message is therefore now left to #wrap_message and renders the same way it does when no entity is declared. Hash and object messages are presented as before. with: and a class's own Entity are untouched.

error! given	master	this PR
{ code: 'x', message: 'm' }	401 presented	401 presented
an object	401 presented	401 presented
'Unauthorized' (any of the three spellings)	500	401 {"error":"Unauthorized"}

Backward compatibility

An entity written to take the String itself (expose(:message) { |message, _| message }) and declared through the block method or http_codes: used to present String messages. It no longer receives them. UPGRADING shows moving it to a Hash message.

Test plan

• Present an error response with the entity a desc failure keyword names #2949's three-spelling loop in endpoint_spec.rb gains a String-message example. All three fail on master and pass here.
• spec/integration/grape_entity/entity_spec.rb covers the same case with a real Grape::Entity. It fails on master and passes here.
• Full RSpec suite passes locally (2913 examples; 2940 with gemfiles/grape_entity.gemfile).
• RuboCop clean.
• CI green.

🤖 Generated with Claude Code

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