One game, one target, every day. Finish a game to keep your streak alive.
The challenge is derived from the calendar date — the day picks the game and the target score through a deterministic seed. There is no server involved, so the same device sees the same challenge all day, and tomorrow brings a different one automatically.
Streaks are credited once per calendar day, and only when you actually finish a game. Reloading the page or reopening a game does nothing, and the streak refuses to advance if the device clock moves backwards.