import type { ModelMessage, UserContent } from "ai";
import type { DeliverPayload, SessionAuthContext } from "#channel/types.js";
import type { StepInput } from "#harness/types.js";
/**
 * Merges two {@link StepInput} values into one.
 *
 * Used by the harness to coalesce deferred step input with the current
 * turn's input, and by the execution layer after calling `onDeliver`
 * for each queued delivery payload.
 */
export declare function coalesceTurnInputs(a: StepInput, b: StepInput): StepInput;
/**
 * Removes text parts with no model-visible content from a user message.
 *
 * Returns `undefined` when no parts remain, allowing callers to omit the user
 * turn entirely rather than create an empty model prompt block.
 */
export declare function normalizeUserContent(content: string | UserContent | undefined): string | UserContent | undefined;
/**
 * Extracts the final visible assistant text from model response messages.
 *
 * Prefers text extracted from the last assistant message that contains visible
 * text. Falls back to the raw `text` property from the AI SDK result when no
 * assistant message contains text. Returns `null` when neither source contains
 * text.
 */
export declare function resolveAssistantStepText(messages: readonly ModelMessage[], fallback: string | undefined): string | null;
/**
 * Appends user content while preserving structured attachment parts.
 */
export declare function appendUserContent(input: {
    readonly appended: string | UserContent;
    readonly existing: string | UserContent;
}): string | UserContent;
/**
 * Structural shape of the workflow `DeliverHookPayload`. Using a
 * structural type keeps this helper decoupled from the concrete
 * runtime type.
 */
interface DeliverLike {
    readonly auth?: SessionAuthContext | null;
    readonly kind: "deliver";
    readonly payloads: readonly DeliverPayload[];
}
/**
 * Coalesces an array of deliver-like items into a single item by
 * collecting all payloads and keeping the most recent auth value.
 *
 * Used by the workflow runtime to batch follow-up deliveries that
 * arrived while a turn or subagent delegation was in progress. Each
 * payload is later passed to `onDeliver` individually so channel-
 * specific fields are never lost.
 */
export declare function coalesceDeliveries<T extends DeliverLike>(items: readonly T[]): T;
export {};