/**
 * Turn state machine. Models the lifecycle of a single agent turn within a session.
 *
 * Sibling of `session-machine.ts`. Keeping them separate (rather than nesting
 * turn state inside session state) matches t3code's split.
 */
import type { TurnState } from "../contracts/provider-runtime.js";
export type TurnEvent = {
    type: "begin";
} | {
    type: "complete";
} | {
    type: "fail";
    reason: string;
} | {
    type: "cancel";
};
export interface TurnTransition {
    readonly from: TurnState;
    readonly to: TurnState;
    readonly event: TurnEvent;
    readonly at: string;
}
export declare function nextTurnState(current: TurnState, event: TurnEvent): TurnState;
export declare function canTransition(current: TurnState, event: TurnEvent): boolean;
export declare function isTerminal(state: TurnState): boolean;
export declare class TurnMachine {
    private state;
    private readonly history;
    constructor(initial?: TurnState);
    current(): TurnState;
    send(event: TurnEvent): TurnTransition;
    log(): readonly TurnTransition[];
}