/**
 * @license
 * Copyright 2026 Steven Roussey <sroussey@gmail.com>
 * SPDX-License-Identifier: Apache-2.0
 */
import type { StreamEvent, TaskOutput } from "@workglow/task-graph";
/**
 * Stateful accumulator that materialises a single output `T` from a sequence
 * of {@link StreamEvent}s.
 *
 * - `text-delta` per port → concatenated per port (`Map<port, string>`).
 * - `object-delta` non-array → replace semantics (each delta is a more
 *   complete partial snapshot — last wins per port).
 * - `object-delta` array → upsert by `id` per port.
 * - `snapshot` → replace running state (last snapshot wins).
 * - `phase` → ignored (metadata only).
 * - `error` → throws immediately at observe time.
 * - `finish` → captured separately via {@link observeFinish}; mandatory before
 *   {@link materialize}.
 *
 * Mixed-mode (both text-delta and object-delta on the same stream) is
 * rejected at materialise time.
 *
 * This accumulator is **only** instantiated at explicit terminal-consumer
 * sites (AiTask.execute, StreamProcessor `ctx.shouldAccumulate` branch). Do
 * not use it inside run-fns, workers, AiJob, strategies, or dataflow nodes —
 * streams in this codebase can be conceptually unbounded.
 */
/**
 * Discriminating tag attached to the error thrown by
 * {@link StreamEventAccumulator.materialize} when the underlying stream
 * ended (cleanly or otherwise) without ever emitting a `finish` event.
 * Callers (notably `AiTask.execute`) re-throw with this code preserved so
 * upstream code can distinguish "provider produced no terminal event" from
 * other provider failures.
 */
export declare const ACCUMULATOR_NO_FINISH: "ACCUMULATOR_NO_FINISH";
export declare class StreamEventAccumulator<T extends TaskOutput = TaskOutput> {
    private readonly textAccumulator;
    private readonly objectAccumulator;
    private hasTextDeltas;
    private hasObjectDeltas;
    private hasSnapshots;
    private snapshotAccumulator;
    private finished;
    private finishData;
    /**
     * The `type` of the most recent observed event. Surfaced in the
     * no-finish materialise error so operators can see what the stream
     * trailed off with (e.g. `text-delta`, `phase`, `undefined`).
     */
    private lastEventType;
    observe(event: StreamEvent<T>): void;
    observeFinish(event: Extract<StreamEvent<T>, {
        type: "finish";
    }>): void;
    materialize(): T;
}
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