Replay guarantees

Lumyn is built around a simple contract: decisions you can't replay aren't decisions.

What is replay?

Replay means evaluating a stored Decision Pack / Decision Record against the same engine semantics and inputs, producing the same normalized decision output (excluding decision_id and created_at).

What is guaranteed (v1)

• If you replay the same stored v1 pack with the same Lumyn version, you get the same verdict and reason codes.
• If your policy and memory snapshot are identical, evaluation is deterministic.
• Reason codes are stable machine strings (no dynamic content).

What is not guaranteed

• Different Lumyn versions may change behavior (use version pinning when you need strict reproducibility).
• If you depend on external calls during a decision, you must record their outputs (or stub them) to replay.

Recommended incident workflow

1. Store the Decision Record (and any memory snapshot it depends on).
2. Reproduce via lumyn replay to confirm the verdict and reasons.
3. Label outcomes as events (append-only), then re-run the same request to confirm behavior changes.