`Response.json(data, init)` was refused (SC2020). It now builds a native
Response the way undici does: ResponseInit converts, the data serializes
through the checked-dynamic JSON serializer (toJSON hooks included;
TypeError "Value is not JSON serializable" when JSON.stringify answers
undefined), then the response initializes like the constructor with
"application/json" as the default content type, so status, statusText,
header, and null-body-status errors keep their order.
The fetch compatibility profile moves Response.json from unsupported to a
static operation with the static-response-json differential fixture.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
