Daily chest — one claim per day, clock tricks be damned

daily_chest.cell

// ============================================================================
// DAILY CHEST — one claim per day, clock tricks be damned
// ============================================================================
// Daily-reward double claims — via device-clock manipulation or plain
// request replay — are the most farmed exploit in free-to-play games, and
// "fixes" that compare timestamps keep losing to timezone math. The fix is
// not a better clock check. It is that each (player, day) claim is a
// one-way machine: unclaimed -> claimed, with `claimed` TERMINAL. The
// replayed request has no transition to fire — soma verify proves it. The
// coin ledger's >= 0 invariant keeps the wallet honest on the way through.
// ============================================================================

cell DailyChest {
    face {
        signal claim_chest(player: String, day: String) -> Map
        signal coins_of(player: String) -> Int
    }

    memory {
        coins: Map<String, Int> [persistent, consistent]
        invariant coins >= 0
    }

    // one instance per (player, day) — the smallest possible ratchet
    state chest_claim {
        initial: unclaimed
        unclaimed -> claimed
    }

    on claim_chest(player: String, day: String) {
        let key = "{player}@{day}"
        let r = try { transition(key, "claimed") }
        if r.error != () { return map("ok", false, "reason", "already claimed on {day}") }
        coins.set(player, (coins.get(player) ?? 0) + 50)
        return map("ok", true, "coins", coins.get(player))
    }

    on coins_of(player: String) { return coins.get(player) ?? 0 }
}

cell test ChestTests {
    rules {
        assert claim_chest("zoe", "2026-06-11").ok == true
        assert coins_of("zoe") == 50
        // THE REPLAY: same player, same day — the transition does not exist
        assert claim_chest("zoe", "2026-06-11").ok == false
        assert coins_of("zoe") == 50
        assert_fails transition("zoe@2026-06-11", "claimed")
        // a new day is a fresh machine instance, claimable exactly once
        assert claim_chest("zoe", "2026-06-12").ok == true
        assert coins_of("zoe") == 100
        assert claim_chest("zoe", "2026-06-12").ok == false
        // the wallet itself refuses corruption
        assert_fails coins.set("zoe", -5)
    }
}