The full-codebase mutants run showed ~600 of the 902 surviving mutants
are arithmetic / comparison flips inside algorithm run() bodies — the
per-helper Phase 1 tests don't reach the optimization loop itself, and
the existing deterministic-with-same-seed tests can't catch them (both
the clean and mutated runs use the same seed, so they still match).
This extends the async-parity sweep: each of the 33 parity tests now
also asserts the sync run's result against an exact captured snapshot
(best objectives for single-objective algorithms; sorted pareto-front
objective tuples for multi-objective ones). Any arithmetic flip
anywhere in run() perturbs at least one f64 and breaks the snapshot.
Fixtures are deliberately multi-dimensional — SnapSphere (3-D sum of
squares), SnapMo (3-variable / 2-objective), a 6-city TinyTsp, a 3-D
SnapSpherePartial for Hyperband. A 1-D problem leaves the per-axis /
covariance-matrix / simplex machinery degenerate, so arithmetic
mutations there wouldn't change the result; 3-D exercises the full
loop body.
Snapshots captured from the un-mutated implementation; an intentional
algorithm change requires regenerating them, by design. The assertions
live in the async-gated module because they reuse its per-algorithm
constructions — active during the mutation campaign
(--features async,serde) and under cargo test --features async.