ocess. After `(os/proc-wait proc)` finishes, proc gains a new field, :return-code. If :x flag is passed to os/spawn, non-zero exit code will cause os/proc-wait to raise an error. If pipe streams created with :pipe keyword are not closed in time, janet can run out of file descriptors. They can be closed individually, or `os/proc-close` can close all pipe streams on proc. If pipe streams aren't read before `os/proc-wait` finishes, then pipe buffers become full, and the process cannot finish because the proces