Segments

A segment is a group of players with a name. "Lapsed customers." "Gold tier in Germany." "Anybody who has booked twice."

You set it up once, and every mission, streak and shop listing can point at it instead of repeating the same rule. Change the segment and everything pointing at it changes with it, with nothing to re-save.

Membership is worked out when it is read, so a player joins or leaves a segment the moment they match it or stop matching it. There is no list to refresh.

Leaving takes nothing away. A player already in a mission, a streak or a leaderboard stays in it, because the rule that let them in is checked once. It still decides what they can buy.