# Solution: Event Log, Checkpoints, Memory and Deterministic Replay

## Выбранный подход

Use the existing shared vertical-slice public ports rather than creating a second
event model. Events remain authoritative; live state and checkpoints are derived.
The owned study supplies adversarial acceptance tests and records uncovered
contract gaps.

## Архитектура и поток данных

```text
validated command
-> authoritative engine transition
-> immutable event clone appended with sequence/state versions/visibility
-> live materialized GameState

recovery
-> replayEvents(genesis, allEvents)
-> verifyCheckpoint(genesis, allEvents, checkpoint)
-> replayFromCheckpoint(genesis, allEvents, checkpoint)
   -> reject verification mismatch
   -> replay suffix from verified checkpoint state
-> projectState(actor) using preserved visibility
```

`replayFromCheckpoint` owns verification, so a caller cannot accidentally use a
tampered checkpoint through the public replay path. Summaries and retrieved
memories remain outside the authority boundary.

## Структура прототипа

- `prototype/event-log.verification.test.ts` imports:
  - shared engine and seeded RNG;
  - `InMemoryEventLog`, checkpoint and replay functions;
  - canonical `stateHash`;
  - `projectState`;
  - `runLongSessionReplay`.
- `prototype/README.md` lists exact coverage and gaps.

No duplicate event/reducer/hash implementation is owned by this study.

## Требования

- Verified environment: macOS 26.4 (`25E246`), arm64.
- Runtime: Node.js `v24.14.0` with built-in TypeScript stripping.
- Root dependencies installed according to the shared repository lockfile.
- External services: `none`.

## Установка

From repository root:

```bash
npm install
node --version
```

This study adds no dependency.

## Запуск

From repository root:

```bash
node --test RnD/technical/2026-07-25-event-log-memory-replay/prototype/event-log.verification.test.ts
```

The AC-05 test emits the full JSON replay report as a test diagnostic.

## Тестирование

```bash
node --test RnD/technical/2026-07-25-event-log-memory-replay/prototype/event-log.verification.test.ts
npm run typecheck
```

Fresh scoped result: `5` pass, `0` fail, `0` TODO. Fresh root TypeScript result:
exit `0`.

## Конфигурация

No environment variables or services are used. The shared long fixture has seed
`20260725`; the owned short fixture uses the same seed and checkpoints at half.

## Ограничения и безопасность

- `InMemoryEventLog` is not a durability proof.
- A checkpoint contains a full state clone and hash; storage authentication and
  encryption are out of scope.
- The event union lacks correction metadata.
- The long fixture lacks primary-event-reference and branch-chronology models.
- Synthetic fixtures contain no real player data.

## Условия переноса в production

- Preserve verification inside the checkpoint-replay authority boundary.
- Add an immutable correction event with authorized author, reason and corrected
  event reference.
- Add persistent append atomicity, authorization, backup/restore and migration
  tests.
- Establish cross-runtime canonical-hash vectors.
- Extend the fixed long fixture with branch chronology and primary-event
  references before marking the campaign gate fully passed.