How the sharing works

One shared list. Both of you see the same thing, and every change is signed with your name and the time, so you can tell who ticked what.

If two of you change different tasks at once, both changes survive. If you both change the same task, the later one wins — so it is worth saying out loud who is doing what before a big session.

With no signal it keeps working on the phone and sends the changes up as soon as the signal is back.