System overview

datadata is a library with a clean client/server split and two deliberate seams — the event bus and the storage adapter — that decide where and how it runs.

┌────────────────┐
│ session client │  staging layer (optional)
└───────┬────────┘
        │
┌───────▼────────┐         ┌─────────────────┐
│     client     │◄───────►│    event bus    │  WebSocket / in-process
│   (optimistic  │  events │                 │
│    overlay)    │         └────────┬────────┘
└────────────────┘                  │
                           ┌────────▼────────┐
                           │     server      │
                           │ (authoritative) │
                           └────────┬────────┘
                                    │
                           ┌────────▼────────┐
                           │ storage adapter │
                           │  (SQLite / mem) │
                           └─────────────────┘

The parts

Client — holds subscriptions and the optimistic overlay; exposes the document API to the application (and to framework bindings like the React integration).
Session client — the staging layer, layered on a client.
Server — the authority for one folder: validates against schemas, assigns sequence numbers, persists, broadcasts. Enforces limits (document size, rates) and exposes a change callback for automation.
Event bus — routes protocol events between clients and server. Implementations: WebSocket (production), in-process (server-side agents, tests, demos), and a composite that combines both on one server.
Storage adapter — persistence behind the server: documents, the event log, and Yjs state. The production implementation is SQLite in a Durable Object; tests use memory.

Where it runs today

The current production shape is Cloudflare Workers + Durable Objects: one Durable Object per folder, embedding the server, its storage, and its WebSocket connections. The seams exist precisely so that this is a deployment choice, not an identity — but Cloudflare is the only backend that exists today.