Currently code like this will not work:

for {
  ref    <- Ref.make(0)
  fibers <- ZIO.foreachPar(1 to 100)(_ => ref.update(_ + 1).fork)
  _      <- ZIO.foreach(fibers)(_.await)
  value  <- ref.get
} yield assert(value)(equalTo(100))

The issue is that foreachPar forks a fiber to perform each of the effects and under the supervision model when that fiber terminates it terminates the fibers in its scope, including the fiber that is updating the Ref in this case.

The fix is to use the transplant operator similar to how we did with zipWithPar to make sure that when fibers are forked within one of the effects in foreachPar they are forked on the original scope and not the scope of the fiber internally created by foreachPar. Conceptually this is the same issue as with zipWithPar, it looks like we just didn't push the change through to foreachPar.