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Pull #2693

github

Introduce Grape::Exceptions::ErrorResponse value object

`Middleware::Error#error_response` previously handled three input shapes
polymorphically: a Hash from `throw :error, {...}`, a `Grape::Exceptions::Base`
subclass, and an arbitrary user-handler return. Hash-style access like
`error[:status]` only worked on exceptions because `Grape::Exceptions::Base#[]`
delegated to `__send__` — a "pretend to be a Hash" trick that propped up the
polymorphism in `error_response`.

Introduce `Grape::Exceptions::ErrorResponse`, a small value object with
`status`, `message`, `headers`, `backtrace`, and `original_exception` readers
plus a `coerce(input)` classifier that normalizes Hash, Exception, and
ErrorResponse inputs into a uniform value at the boundary. The middleware now
calls `coerce` once at entry and reads typed attributes — no more polymorphism
puzzle in the body.

Migrated the seven internal `throw :error, hash` sites to throw `ErrorResponse`
instances. User-defined `throw :error, hash` from custom middleware or
`rescue_from` blocks continues to work via `coerce`.

`Grape::Exceptions::Base#[]` is preserved (still delegates to `__send__`) and
covered by new specs. The only contract change is that the `throw :error`
payload is now an `ErrorResponse` value object instead of a `Hash` — see
UPGRADING for migration notes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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