# Replay and compatibility

This page is derived from the [canonical developer-reference](/learn/developer-reference); its content has one source of truth.

## Replay and tamper/version compatibility

Source: `src/game/replay.ts`; tests: `src/game/replay.test.ts`.

Replay v3 is a strict object containing `version: 3`, current `engineVersion`, canonical answers, validated config, integer seed 0–4,294,967,295, `setup_…` request hash, ledger of at most eight entries, and a `replay_…` contract hash. `createReplay` canonicalizes and validates; `encodeReplay` serializes validated replay data; `decodeReplay` validates the decoded object; `playReplay` runs the recorded ledger through the deterministic engine and returns replay/state/snapshot without inference. The optional interpreter parameter is intentionally unused.

Any malformed, tampered, unsupported, or semantically unreachable input is rejected (`Invalid, tampered, or unsupported LifePot replay v3` or `Invalid or unsupported LifePot replay`). The contract hash is a compact FNV-1a integrity checksum, not a cryptographic signature or proof against a determined attacker. A future engine behavior change requires an engine version change and compatibility review; do not claim cross-version support unless explicitly implemented and tested.