this post Still not getting automatic update install - #19 by sam_nazarko
seems to say the osmc staging repo is called -devel
ie deb http://apt.osmc.tv jessie-devel main
that is pretty much the info i was looking for. it just took a while of reading between the lines to get enough context to search for the right thing.
of course I would rather stay on the regular repo and just use the kernel from -devel although i guess that might cause other problems.
BTW I don’t think “if you don’t know already then you shouldn’t ask” is a helpful approach to learning this stuff