/**
 * `StateClient` — observer for QAR's `state.update` envelopes.
 *
 * State updates are per-skill mutations: a `skill` keys the schema and `op`
 * (`patch` / `replace` / `init`) describes the mutation kind. The payload
 * shape is typed by QAR (codegen overlay in `src/qar/payloads.ts`); the
 * filter helper here narrows by skill so consumers can wire one handler
 * per skill without de-multiplexing themselves.
 *
 * `state.update` is bidirectional in QAR's wire model; this surface is
 * server→client only (the inbound stream). SDK-side emission for
 * skill-managed state pushes is reserved for a future ticket.
 */
import type { StateUpdateEnvelope } from '../qar/envelopes.js';
import { KindObserverClient } from './observers.js';
import type { EventSubscription } from './observers.js';
/** Filter for `state.update` envelopes. */
export interface StateFilter {
    /** Match against `payload.skill` — the skill key whose state is mutating. */
    readonly skill?: string;
}
export type StateHandler = (env: StateUpdateEnvelope) => void;
export declare class StateClient extends KindObserverClient<'state.update', StateUpdateEnvelope> {
    /**
     * Register a handler invoked for every inbound `state.update` envelope.
     *
     * Same multi-handler / fan-out / throw-swallowing semantics as the other
     * observer surfaces. The two-arg overload accepts a `StateFilter` (only
     * `skill` for now — `op` would be cheap to add but we'd rather grow the
     * filter when consumers ask).
     */
    onUpdate(handler: StateHandler): EventSubscription;
    onUpdate(filter: StateFilter, handler: StateHandler): EventSubscription;
}
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