It probably broke at some point during the refactoring -- we need to check the socket.io story, see this commentary:

-- | A customised configuration file that the "notes" service would otherwise send us, that -- overrides the 'urlpath' to contain the proper service path, so that the websocket connection -- can be started correctly. If we do not override the 'urlpath', due to the way things work -- internally, the Javascript of CodiMD would otherwise take the first slice of the URL path -- (something like /notes/<frameId>) and use /that/ as the , which would be wrong -- as it would try to establish a connection to noteId=notes.