Masking polymorphic effect

[Flecheck]

Hello,

effect test<a>
  fun test() : a

fun x(f : () -> <test<string>,test<a>|e> b, g : () -> e a): e b
  with fun test()
    g()
  with fun test()
    "boo"
  f()

I would want to mask test<a> from f but I cannot see how to do it.

If I mask behind, g is infered to be () -> e string

And everything else I tried doesn't compile.