>>>Also there doesn't seem to be any
>>>target for tpic.
> 
> cd /sys/src/cmd/tex/tpic; mk install
> 
> what was the problem with pic?

Thanks; Russ also hinted at that.

I was mostly fighting myself.  It's been a while since I pic'ed. I did
have a couple of suicides with tpic on some bad input. I didn't investigate,
but I can try to investigate it when I have some time.

The man page for pic includes two identical examples; I'm not smart
enough to know if that is on purpose ☺

FYI, I was building a pic that shows the steady-state process/data flow
in srvold9p.  I've attached in case somebody is interested.