evalv3: "field not allowed" regression with hidden field

[mvdan]

env CUE_EXPERIMENT=evalv3=0
exec cue export

env CUE_EXPERIMENT=evalv3=1
exec cue export

-- input.cue --
package p

#Component: {
	kind: string
	output: {}
}

foo: #Component & {
	kind: string
	if kind == "foo" {
		_hidden: {}
	}
}

foo: kind: "foo"

as of `62b21c8c44e84ca6b45224562298b1102b825766:

> env CUE_EXPERIMENT=evalv3=0
> exec cue export
[stdout]
{
    "foo": {
        "kind": "foo",
        "output": {}
    }
}
> env CUE_EXPERIMENT=evalv3=1
> exec cue export
[stderr]
foo._hidden: field not allowed:
    ./input.cue:11:12
    ./input.cue:11:3
[exit status 1]
FAIL: ../repro-evalv3.txtar:5: unexpected command failure

This definitely seems wrong - hidden fields should not be affected by closedness.