I tried that and about a million other things in Ubuntu. When I hit tab I see options, but nothing I put in my .zshrc will allow me to use the arrow keys or anything else to navigate the completion list.
I am using oh my zsh but I tried turning it off and it didn't seem to matter.
How do you track of multiple tasks/projects with this technique? One calendar per task? A key/value mapping to replace the cross (e.g. a "G" for every day you go to the gym)? Simply merging them into one "meta" task? Or does it just not work for more than one task?
I since stumbled upon Giles Bowkett's variation whereby he uses a colour-coded horizontal line for each task. I like it. It emphasises the "chain" aspect and works well within the space constraints.
With the help of Stackdump (https://bitbucket.org/samuel.lai/stackdump/), I've hacked out a useable mirror from the provided XML data dump.