Partner is back at work, from the spare room, and somehow that's harder than an office

On paper it's great. Another adult in the house all day, lunch together, help if I need it. In reality there's a closed door with calls behind it, and every time the baby cries I'm doing the maths on whether it's worth knocking. Yesterday I stood outside that door with a screaming two month old for five minutes waiting for a call to end. It didn't end. My parents come on Tuesdays and Thursdays, so it's the other three days. How did you two decide what counts as a fair interruption? We need a rule that isn't 'only if something is on fire' :D