# Artifact compatibility

MoonLab separates three deterministic artifacts:

- Replay JSON binds Scenario and model identity, normalized inputs, Resource Budgets, Seed, and Decision Stream to a replay-compatibility version.
- Trace JSONL explains selected actions and observable consequences in order.
- Run Report JSON summarizes the Run Outcome/Failure Signature, Scenario and model identities, action/time totals, peak pending work, Message delivery/drop counts, and Crash/Restart statistics.

Replay validates schema version, replay-compatibility version, engine identity, model identity, and the normalized SHA-256 Scenario identity before execution. A mismatch is `IncompatibleArtifact`. `ReplayDiverged` is reserved for a compatible artifact whose next recorded choice is not available in the current enabled set. Replay never falls back to randomized exploration.

Artifact schemas are independently versioned from the library's semantic version. Pre-1.0 library releases may evolve Interfaces, but a schema or replay-compatibility change must be explicit.