[jorgefilipecosta]

Follow up to #14547 (comment).

This PR adds three route and handler options that let a route opt out of the global response processing:

• allow_fields: when false, the _fields parameter does not filter the response data.
• allow_embed: when false, the _embed parameter does not embed linked resources. The links are still added as _links.
• allow_links: when false, the response links are not added to the response data as _links.

All three default to true. A handler option takes precedence over the route option of the same name, as with allow_batch. The new WP_REST_Server::is_response_option_enabled() method reads them from the matched route and handler. The options apply to served, enveloped and preloaded requests.

register_rest_route(
	'my-ns/v1',
	'/run',
	array(
		'methods'             => 'GET',
		'callback'            => 'my_callback',
		'permission_callback' => '__return_true',
		'allow_fields'        => false,
		'allow_embed'         => false,
		'allow_links'         => false,
	)
);

This lets a route return its data unchanged, e.g. the abilities run endpoint, whose result follows the ability's output schema and can be an object, a list or a scalar value. #14547 uses these options for that endpoint.

Drafted with AI assistance and reviewed by me.

Trac ticket: https://core.trac.wordpress.org/ticket/66267

Testing

Verify unit tests are passing:

npm run test:php -- --filter 'Tests_REST_Server' --group 66267

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