evalv3 regression where schema used via LookupPath and FillPath causes "field not allowed"

[mvdan]

# Uncomment as needed:
# exec go mod edit -replace=cuelang.org/go=/home/mvdan/src/c/cue

exec go mod tidy

env CUE_EXPERIMENT=evalv3=0
exec go run main.go

env CUE_EXPERIMENT=evalv3=1
exec go run main.go
-- go.mod --
module test

go 1.23

require cuelang.org/go v0.13.0-alpha.1.0.20250318153901-c479844b8d7a
-- main.go --
package main

import (
	"fmt"
	"os"

	"cuelang.org/go/cue"
	"cuelang.org/go/cue/cuecontext"
)

func main() {
	ctx := cuecontext.New()

	v := ctx.CompileString(`
		_schema: _
		_schema
		apiVersion: "foo"
		spec: group: "foo"
	`)
	schema := ctx.CompileString(`
		#Schema: {
			spec!: group!: string
		}
	`).LookupPath(cue.MakePath(cue.Def("#Schema")))

	v = v.FillPath(cue.MakePath(cue.Hid("_schema", "_")), schema)

	if err := v.Validate(); err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
	fmt.Println("Success")
	os.Exit(0)
}

As of c479844:

> env CUE_EXPERIMENT=evalv3=0
> exec go run main.go
[stdout]
Success
> env CUE_EXPERIMENT=evalv3=1
> exec go run main.go
[stdout]
apiVersion: field not allowed
[stderr]
exit status 1
[exit status 1]
FAIL: repro-go.txtar:10: unexpected command failure

[mvdan]

Here is a pure CUE reproducer:

# With the old evaluator.
env CUE_EXPERIMENT=evalv3=0
exec cue export

# With the new evaluator.
env CUE_EXPERIMENT=evalv3=1
exec cue export

-- input.cue --
package p

_schema
apiVersion: "foo"
spec: group: "foo"

#Schema: {
	spec!: group!: string
}

_schema: #Schema

# With the old evaluator. (0.023s)
> env CUE_EXPERIMENT=evalv3=0
> exec cue export
[stdout]
{
    "spec": {
        "group": "foo"
    },
    "apiVersion": "foo"
}
# With the new evaluator. (0.048s)
> env CUE_EXPERIMENT=evalv3=1
> exec cue export
[stderr]
apiVersion: field not allowed:
    ./input.cue:4:1
[exit status 1]
FAIL: repro-evalv3.txtar:7: unexpected command failure

[mvdan]

I will reopen this one if that's okay, because it turns out that you fixed my pure CUE reproducer in my last comment, but the original Go code is still broken on evalv3.

I tried reducing it into pure CUE again, and I think I have it once again:

# With the old evaluator.
env CUE_EXPERIMENT=evalv3=0
exec cue export

# With the new evaluator.
env CUE_EXPERIMENT=evalv3=1
exec cue export

-- input.cue --
package p

apiVersion: "foo"
spec: group: "foo"

#Schema

#Schema: close({
	spec!: group!: string
})

As of 2c002ae:

# With the old evaluator. (0.010s)
> env CUE_EXPERIMENT=evalv3=0
> exec cue export
[stdout]
{
    "spec": {
        "group": "foo"
    },
    "apiVersion": "foo"
}
# With the new evaluator. (0.023s)
> env CUE_EXPERIMENT=evalv3=1
> exec cue export
[stderr]
apiVersion: field not allowed:
    ./input.cue:3:1

[mvdan]

Leaving this open because the original Go code still fails as of e311d45.