Support the "onCancel associates over uncancelable boundary" law (ZIO 2/CE 3)

[johnspade]

Explore how, if at all, this behavior can be supported. Context and discussions: #616

This feels like it will be a difficult property to support precisely because it doesn't support equational reasoning and arguably relies on an implementation detail of interruption only being checked for between certain operations.

[ollyw]

Is there any progress on this? I have a sneaking suspicion that this is the cause of some issues which I seeing with Http4s with Blaze when upgrading to CE 3.4.x. I have some circumstantial evidence but no minimised reproducer yet. It would help to know if this is 1) Not going to be implemented 2) Is shortly 3) Not for a long while