Looks like the last code commit from #BSD #csh to get into #illumos was:
1990-07-01: strerror(); set proc in pgrp before setting terminal
Marc Teitelbaum
https://github.com/dspinellis/unix-history-repo/commit/c6261f671d723bf1898e8e05b1aa3b9ac00164e8
The first code commit from BSD csh not in illumos was:
1990-11-09: remove vestiges of AT&T shell
Keith Bostic
https://github.com/dspinellis/unix-history-repo/commit/46d46a70cd3ce5b5996e53856a3ef77a8cdd2fcf
Oh, the irony.
#unix