# Determinism Policy

MabeLabRS emphasizes reproducibility of artificial life experiments.

## Randomness
- Use `rand_chacha::ChaCha8Rng` (fast, reproducible).
- Seeds must be explicit and logged in experiment manifests.

## Floating-point
- Default: `f64`.
- Avoid nondeterministic parallel reductions; when needed, gate behind
  the `fast-math` feature.
- Golden tests should tolerate ≤ 1e-12 relative error in float comparisons.

## Collections
- Use `BTreeMap`/`BTreeSet` when deterministic ordering is required.
- Use `indexmap::IndexMap`/`IndexSet` for hash-backed structures
  that preserve insertion order.

## Parallelism
- Sequential by default.
- `rayon` parallelism only behind `parallel` feature flag.
- Golden tests must run with `--no-default-features` to guarantee determinism.