Function autobalance 

pub fn autobalance<S: Clone, R: Sides>(
    stage: &S,
    knobs: &[&dyn Knob<S>],
    entrants: &[&dyn Entrant<S, R>],
    checks: &[Check],
    settings: &BalanceSettings,
) -> Result<Balanced<S>, PlaytestError<R>>
where
    R::Command: Clone,
    R::Outcome: Debug,

Changes stage with knobs until every rate check of checks puts every one of entrants inside its band, as settings says. The entrants and the checks are never changed: only the stage is.

All deterministic:

1. Before: the stage as authored plays at settings.tries. In every band already, it stops (Stop::AlreadyInBands).
2. Pattern search at settings.quick tries, from every knob at 0, each knob’s stride its Knob::stride: in knob order, +stride then -stride (clamped to the range, skipping a step that doesn’t move or that a knob can’t apply). The first step that lowers the distance is taken and the knob order starts again. When none does, every stride above 1 is halved; when every stride is 1, it stops (Stop::Stuck).
3. Confirm: a setting in every band at quick plays at tries. In every band there too, it is pruned; if not, the pattern search carries on at tries from there.
4. Prune: each changed knob in order is tried at 0, then nearer 0 one step at a time, keeping each change that stays in every band at tries (Stop::InBands). What is left is the smallest change set this search found, not one proved the smallest.
5. Budget: every run of the playtest runner is one evaluation, and a setting is never run twice at one try count. When the evaluations run out, it stops (Stop::Budget) with the best setting seen, kept back one evaluation to play it at tries.

A setting that ends no nearer its bands at tries than the stage as authored is dropped: the result is then the stage as authored.

A check naming an entrant not in the run fails before any try is played; a refused command stops the search.

It is autobalance_by, each setting played by playtest::run, never told to stop.