this.setState() merges a patch into the actor’s current state. Use it for small
structured values you want to read quickly — the current conversation state, user
preferences, last-seen timestamp.
setState is a recursive merge (RFC 7396) — top-level keys you pass are merged in,
nested objects are deep-merged, and null deletes a key. replaceState replaces the
whole state object.
State is one value, read whole. The moment data turns relational or queryable —
orders, events, anything you’d filter or aggregate — put it in the actor’s embedded
SQL database instead.