openapi export: (ExpandReferences: true) unsupported op for number &

[tvi]

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

$ cue version
cue version v0.15.0-rc.1

CUE language version v0.15.0

Go version go1.25.3
      -buildmode exe
       -compiler gc
       -trimpath true
     CGO_ENABLED 0
          GOARCH arm64
            GOOS darwin
         GOARM64 v8.0

What did you do?

a.cue

#def: {
        a: *100 | int64
        b: int64
}

cue def a.cue --out openapi+yaml

When running under default cue v0.15.0-rc.1 I get two quite different outputs for a and b

openapi: 3.0.0
info:
  title: Generated by cue.
  version: no version
paths: {}
components:
  schemas:
    def:
      type: object
      required:
        - a
        - b
      properties:
        a:
          type: integer
          minimum: -9223372036854775808
          maximum: 9223372036854775807
          default: 100
        b:
          type: integer
          format: int64

But when running under custom build where https://github.com/cue-lang/cue/blob/82c321f237881dea51d0b383d3579ba6746a6acc/internal/encoding/encoder.go#L84 is set to ExpandReferences: true like

case build.OpenAPI:
		cfg := &openapi.Config{
			ExpandReferences: true,
		}

Upon running the command, I get following error:

cue def a.cue --out openapi+yaml
#def.a: unsupported op for number &