evalv3: strange behaviour with chaining of list comprehensions

[myitcv]

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

$ cue version
cue version v0.0.0-20240507175810-9efad9041981

go version go1.22.1
      -buildmode exe
       -compiler gc
  DefaultGODEBUG httplaxcontentlength=1,httpmuxgo121=1,tls10server=1,tlsrsakex=1,tlsunsafeekm=1
     CGO_ENABLED 1
          GOARCH arm64
            GOOS linux
             vcs git
    vcs.revision 9efad90419811c9a27682857ffdc9324cdb7e094
        vcs.time 2024-05-07T17:58:10Z
    vcs.modified false
cue.lang.version v0.9.0

Does this issue reproduce with the latest release?

Yes

What did you do?

# old evaluator
env CUE_EXPERIMENT=''
exec cue export x.cue
cmp stdout stdout.golden

# new evaluator
env CUE_EXPERIMENT='evalv3'
exec cue export x.cue
cmp stdout stdout.golden

-- x.cue --
import "math/bits"

x: [...bool]
x: [true, false, true, true]
y: [for _, v in x {[if v {1}, 0][0]}]
z: [for i, v in y {bits.Set(*z[i-1] | 0, len(y)-i-1, v)}][3]

-- stdout.golden --
{
    "x": [
        true,
        false,
        true,
        true
    ],
    "y": [
        1,
        0,
        1,
        1
    ],
    "z": 1
}

What did you expect to see?

Passing test.

What did you see instead?

# old evaluator (0.012s)
# new evaluator (0.011s)
> env CUE_EXPERIMENT='evalv3'
> exec cue export x.cue
[stderr]
z: error in call to math/bits.Set: non-concrete value _:
    ./x.cue:6:20
[exit status 1]
FAIL: /tmp/testscript820382168/repro.txtar/script.txtar:8: unexpected command failure

Note that it is understood that the reference in the declaration of z to *z[i-1] | 0 is "wrong" by virtue of the result of z being a scalar value (contrast https://cuelang.org/play/?id=MSdriK7Ernf#w=function&i=cue&f=eval&o=cue) but reporting this actual error for completeness' sake.