PackageImports chooses an arbitrary component when there are multiple libraries in a package

I have a cabal file which declares a few sublibraries.

cabal-version:   3.0
name:            rexp-demo
version:         0.1.0.0
license:         NONE
author:          matthewtpickering@gmail.com
maintainer:      Matthew Pickering
build-type:      Simple
extra-doc-files: CHANGELOG.md

common warnings
    ghc-options: -Wall

executable rexp-demo
    build-depends: rexp-demo, base
    main-is: Main.hs

library
    import:           warnings
    exposed-modules:  MyLib
    build-depends:    base ^>=4.18.0.0, a, b
    hs-source-dirs:   src
    default-language: Haskell2010

library a
  exposed-modules: A
  hs-source-dirs: src-a
  build-depends:    base ^>=4.18.0.0

library b
  exposed-modules: A
  hs-source-dirs: src-b
  build-depends:    base ^>=4.18.0.0

When I use package imports to "disambiguate" then this program compiles and chooses (arbitrarily library a to provide the A module).

{-# LANGUAGE PackageImports #-}
module MyLib (f) where

import "rexp-demo" A

f = a

If I remove the package import then it complains about an ambiguous module.

src/MyLib.hs:6:1: error:
    Ambiguous module name ‘A’:
      it was found in multiple packages:
      rexp-demo-0.1.0.0:a rexp-demo-0.1.0.0:b
  |
6 | import A
  | ^^^^^^^^

The program shouldn't choose arbitrarily (or via some rule) to prefer a over b.

Ideally the PackageImports extension should have a syntax to allow me to precisely state that I want library a or library b.