evaluator: unification of closed struct in subfield does not close it

[rogpeppe]

What version of CUE are you using (cue version)?

cue version v0.0.0-20220815180243-e187f9fe5d45

       -compiler gc
     CGO_ENABLED 1
          GOARCH amd64
            GOOS linux
         GOAMD64 v1
             vcs git
    vcs.revision e187f9fe5d456f14073645670a98803d3048849e
        vcs.time 2022-08-15T18:02:43Z
    vcs.modified false

Does this issue reproduce with the latest release?

yes

What did you do?

! exec cue export ok1.cue
! exec cue export ok2.cue
! exec cue export bug.cue

-- ok1.cue --
#T: close({})
#T: {...}
x: #T
x: foo: "foo"

-- ok2.cue --
#S: {}
#T: s: #S
#T: s: {...}
x: #T.s
x: foo: "foo"

-- bug.cue --
#T: s: close({})
#T: s: {...}
x: #T.s
x: foo: "foo"

What did you expect to see?

The testscript should pass (i.e. all those CUE examples should fail to export)

What did you see instead?

The bug.cue example succeeds inappropriately.