Snapshot restoration

Set snapshotting: Snapshot.define({ schema, policy }) and use .implement({ init, methods, snapshot }). init(id) exclusively infers runtime state. For a common Ref<State> whose saved value matches the schema, use snapshot: Snapshot.ref<Saved>(). For a custom representation use { save: state => Effect<Saved>, restore: (saved, context) => Effect<State> }. When SQLite databases are declared, add databases: state => ({ declaredName: state.handle }) to that strategy. The runtime restores database images before constructing methods.

Use Snapshot.custom({ policy }) with implementation save/restore only for user-managed bytes. Ordinary agents omit snapshot. External PostgreSQL, MySQL, and Ignite state is not included.

Use host-backed Durability combinators around external effects. Do not add compatibility migration envelopes or legacy initialize/restore factories.