<for posterity.;
I pieced together what happened:
I did NOT have a static IP address set on the unraid server like I remembered. Instead, I had a DHCP reservation set on my router. I vaguely remember doing this when my ISP decided to change DNS servers and not tell anyone. Using a reservation let me keep the local IP address the same but passed through whatever name servers the ISP decided on. That's the piece I forgot.
A few days ago, my router decided to revert back to factory settings so I lost that reservation.
My mistake was not associating the router event with the problem accessing the unraid server via the web interface.
So - I got a random IP address assigned to the unraid server. The IP addresses on the dockers didn't change so they kept working. My shares are "remembered" by OS-X (as opposed to a script I used to use to mount drives) so those kept working.
Mystery solved (except for why my router decided to reset to factory settings - but that's for another day).
