The problem

Five people write the notes of a planning meeting in one shared document. Lea types the decisions in section 2 while Omar fixes a date in the paragraph just above. Two others add action items at the bottom.

At 14:32 Omar’s Wi-Fi drops for 20 seconds. He keeps typing. When it comes back, his date fix and Lea’s decisions must both be in the document, in the right places, on all five screens.

You design the server side of that editor, and the rule that decides whose change goes first.