error condition returned to emacs?

Nobody has claimed this yet.

Is there global handling of ocaml exceptions raised from code (inside a defun) invoked
from emacs ?
I ask since my emacs crashes with
```
Fatal Error: executable program file not found
```
when I do invalid_arg "..." .
I haven't found anything in the ecaml source yet to indicate a particular
way of returning an error condition back to emacs.

I haven't wrapped my head around the control model between emacs/ecaml/user-code
yet but happily I tried starting a thread before returning a result back to emacs
and that continues running fine.
is this safe to do or should things be done through Async (or ...) ?

thanks.

Start by tracing the exception boundary for OCaml code invoked from an Emacs defun and reproduce the invalid_arg case that reports “Fatal Error: executable program file not found.” Check how errors are returned to Emacs and whether a thread started before returning a result is supported or must use Async; document the observed safe behavior.

Written by the indexing model from the issue text.