TODO
TODO
Add Lib.Applicative (partitionA)
Name the not-yet-distinguished input/output paths
open_common/fopen_common to call actual open
Move open handling below, start with simple cases
fs_override.c: Remove unused return type macro parameter
Extract Lib.FSHook.OutputBehavior
Annotate undelayed outputs with the actual effects (MISSING SOME EFFECTS).
Only record delayed/undelayed outputs that actually had effects.