State

State is the current value of all properties across all entities, versioned by revision.

Purpose

Hold in-memory state and emit deltas to frontends efficiently.

Backend → Runtime

pump.update(pressure=6.3, temperature=42.3)

Runtime → Frontend (WebSocket delta)

{
  "entity": "pump-01",
  "revision": 106,
  "changes": { "pressure": 6.3 }
}

Fetch full state

GET /state

{
  "pump-01": {
    "revision": 106,
    "values": { "pressure": 6.3, "temperature": 42.3, "power": true }
  }
}

Bandwidth controls

• Number(max_rate=2) — at most 2 updates/sec to frontend
• Number(deadband=0.1) — skip changes smaller than 0.1

Both reduce runtime→frontend emission only. Upstream ingestion is never throttled.

Constraints

• State is in-memory for MVP (no database)
• Revision increments only when a change is actually emitted

Common mistakes

• Assuming update() always emits — deadband/rate can suppress it (returns None)
• Writing values directly to _state instead of using update()