I built Honest Mailbox (my project, link at the bottom), a couples app with a draw-and-guess game, Four in a Row and card decks. All game logic is pure functions on the client, and security rules decide who can touch a game. Drawings are stored as compact strings on a 0–1000 grid, split into chunks so no single write gets big.

Open questions:

• Each stroke is a separate Firestore write. Is that fine at two-user scale, or should I batch?
• Is client-side scoring acceptable when both players are trusted partners?
• Would you use rules-only access control for something like this?

www.honestmailbox.com