Ok, so I'm not on the latest version. I saw a date newer than my compose file and made an incorrect assumption. I'm in the middle of a recording now but will update to the new version after it's done. FWIW I manage with Dockge which is essentially just a frontend to docker compose commands.
As an aside, this reminds me a lot of the early days of MythTV. Smart people like yourselves programming their way through issues while untrained but persistent users like me keep testing and asking for help, rinse and repeat. I think we'll get there eventually and Channels DVR can fade back into the "just works" category 
