Tournament bracket — eliminated means eliminated

tournament_bracket.cell

// ============================================================================
// TOURNAMENT BRACKET — eliminated means eliminated
// ============================================================================
// Online tournament platforms keep having bracket-integrity incidents: an
// admin "fixes" a reported result and a knocked-out player reappears in the
// semifinals, or a player skips a round entirely. Fighting-game brackets on
// early smash.gg/Challonge saw enough of this that audit logs were added.
// The integrity rule is structural here: ELIMINATION IS PERMANENT, CHAMPION
// IS FINAL, and the only way into a round is winning the previous one.
// soma verify proves it: `eliminated` and `champion` have no outgoing edges,
// and no edge skips a round.
// ============================================================================

cell Bracket {
    face {
        signal record_win(player: String) -> Map
        signal record_loss(player: String) -> Map
        signal standing(player: String) -> String
    }

    state progress {
        initial: quarterfinal
        quarterfinal -> semifinal
        semifinal -> final
        final -> champion
        quarterfinal -> eliminated
        semifinal -> eliminated
        final -> eliminated
    }

    on record_win(player: String) {
        let here = get_status(player)
        let next = ""
        if here == "quarterfinal" { next = "semifinal" }
        if here == "semifinal" { next = "final" }
        if here == "final" { next = "champion" }
        if next == "" { return map("ok", false, "reason", "{player} is {here}: no match to win") }
        transition(player, next)
        return map("ok", true, "advanced_to", next)
    }

    on record_loss(player: String) {
        let r = try { transition(player, "eliminated") }
        if r.error != () { return map("ok", false, "reason", "{r.error}") }
        return map("ok", true)
    }

    on standing(player: String) { return get_status(player) }
}

cell test BracketTests {
    rules {
        // ada wins through every round to the title
        assert record_win("ada").ok == true
        assert standing("ada") == "semifinal"
        assert record_win("ada").ok == true
        assert record_win("ada").ok == true
        assert standing("ada") == "champion"
        // CHAMPION IS TERMINAL — no further matches, no retroactive demotion
        assert record_win("ada").ok == false
        assert record_loss("ada").ok == false
        assert_fails transition("ada", "eliminated")
        // bob loses in the quarters — elimination is permanent
        assert record_loss("bob").ok == true
        assert standing("bob") == "eliminated"
        assert_fails transition("bob", "semifinal")
        assert record_win("bob").ok == false
        // rounds cannot be skipped, even by an admin "fixing" the bracket
        assert_fails transition("cleo", "final")
        assert_fails transition("cleo", "champion")
    }
}