# Architecture

## Core Concepts
- **Reducer**: Pure function `newState = Reduce(oldState, Transition)`.
- **WAL**: Append-only log of proposed & accepted transitions.
- **Checkpoint**: Periodic snapshot; on restart: `rehydrate = checkpoint + WAL.replay()`.
- **HLC**: Hybrid Logical Clock stamped on every transition for total ordering.
- **Guards**: Pure predicates sourced from policy, BACKBEAT window, health probes, quorum certs.
- **Compensation**: Inverses for PROVISION, ELECT, INDEX, etc.

## Statechart (overview)
Top-level regions: BOOT, PROJECT_LIFECYCLE (parallel: Ingestion, Council, Environment), EXECUTION (PLAN → WORK → REVIEW → REVERB), CONTROL (PAUSED/DEGRADED/RECOVERY), QUARANTINED, TERMINATED.

See `docs/statechart.yaml` for machine-parseable spec.