[fix] Cannot get props in errors returned by shadowed route #4303

[aolose]

Allow display custom error message from shadow.

e.g

export function get() {
	return {
		body: {
			error: 'A custom error message'
		},
		status: 451
	};
}

fix: #4303

test:

cd packages\kit\test\apps\basics
npx  playwright test -g 'Display custom error message on client side shadow page'
npx  playwright test -g 'Display custom error message on server side shadow page'

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[ItalyPaleAle]

Should this be message or error?

[aolose]

I think error is more explicit.

[ItalyPaleAle]

Thank you for submitting a PR this quickly after I opened an issue :)

[Rich-Harris]

Thank you — this is being worked on in #4032