Messaging and Events

Message Bus

• In-Memory Message Bus — Synchronous dispatcher routing commands, queries, and events to registered handlers
• Command Sender — Thin adapter implementing CommandSenderPort; fire-and-forget
• Event Publisher — Thin adapter implementing EventPublisherPort; publishes domain events
• Query Fetcher — Thin adapter implementing QueryFetcherPort; dispatches queries, returns typed results

Event Store

Append-only event log storing domain events chronologically. Supports append with optimistic concurrency (expected version check) and get_events for aggregate rebuilding.

Event Bus

Publish/subscribe mechanism delivering domain events to registered handlers. Synchronous delivery to all subscribers.

When to use

Use the in-memory message bus for tests and development. Register handlers at startup, dispatch messages at runtime. Use CommandSender, EventPublisher, and QueryFetcher as thin wrappers that satisfy the corresponding port protocols.