I just noticed this revert - I can see what was wrong - the mktemp was missing the -t option so it was creating the pipe in the current folder (also this option is not available on the macOS (BSD) version of mktemp). Though, the trap should have been cleaning up the pipe, regardless...

This is what it should have been to be platform-independent (and correctly in the temp-dir):

: "${TMPDIR:=/tmp}"
PIPE=$(mktemp -u "${TMPDIR%/}/mise.{task}.XXXXXXXX")

I can make a PR again to fix this (and check the trap logic...), unless you want to stick with the STAGED approach (which as previously discussed won't work with files that have spaces).