Catalog-agnostic server-side core for the business event stream (daemon ↔ renderer over WebSocket). The Go counterpart to @tutti-os/event-stream-core.

It owns the in-memory pub/sub registry, scope routing and session fan-out:

Service[S comparable] — sessions, subscriptions, scoped publish/fan-out
Session[S] — per-connection outbound event channel
the catalog contract (Catalog, Direction, ValidationError, …)

Each Session has a bounded queue sized to absorb normal local producer bursts. The registry never blocks a business producer on a slow consumer and never grows the queue without bound. If the queue fills, the Session is closed; the product WebSocket adapter must surface that closure to its client so reconnect and authoritative reconciliation can recover any missed optimistic events.

It is generic over the scope type S and depends only on an injected Catalog (minimal: TopicVersion / ValidatePublish / ValidateSubscription) plus a ScopeNormalizer[S]. It contains no concrete topics. Each product binds its own scope and catalog:

tutti workspace → Service[EventScope] where EventScope = { WorkspaceID }
group chat → Service[RoomScope] where RoomScope = { RoomID }

The WS frame encode/decode (which is woven through the generated protocol types) stays in each product's API layer and calls this registry.