Module persistence 

Persistence Layer - Storage Abstractions

This module defines the core storage traits for the Enact execution engine. The kernel interacts only with these traits; concrete implementations live in the enact-persistence crate.

Store Roles

Store	Role	Mutable?	Authoritative?
EventStore	Source of truth	Append-only	Yes
StateStore	Cache/snapshot	Yes	No
VectorStore	Semantic recall	Yes	No

Key Invariants

1. Kernel NEVER imports concrete implementations
2. All stores implement StorageBackend for mode validation
3. EventStore is append-only and authoritative
4. StateStore/VectorStore are non-authoritative caches

@see docs/TECHNICAL/14-PERSISTENCE-LAYER.md

Modules

guarantees

Store guarantees - documented contracts for each store type

Structs

CollectionInfo

Information about a collection

CostInfo

Cost information for billing

ExecutionSnapshot

Execution state snapshot

ExecutionStats

Execution statistics for a message

InMemoryMessageStore

In-memory implementation of MessageStore

Message

A message in a thread (AI SDK compatible)

MessageMetadata

Message metadata (AI SDK compatible)

StoredEvent

A stored event with metadata

Thread

A conversation thread containing messages

TokenUsage

Token usage for billing and analytics

VectorDocument

A document with embedding for vector storage

VectorFilter

Filter for vector search

VectorSearchResult

Search result with similarity score

Enums

DistanceMetric

Distance metric for similarity calculation

ExecutionEventData

Event data that can be stored

FinishReason

Why the response finished

MessagePart

Message part for rich content (AI SDK compatible)

MessageRole

Message role (AI SDK compatible)

Traits

EventStore

EventStore trait - append-only event log

MessageStore

MessageStore trait - thread/message persistence

StateStore

StateStore trait - mutable snapshot cache

StateStoreJsonExt

Extension trait for JSON operations on StateStore

StorageBackend

Base trait for all storage backends

VectorStore

VectorStore trait - semantic memory