export interface IPlaygroundExecutionAttempt {
    /** Signal passed through every cancellable step owned by this attempt. */
    readonly signal: AbortSignal;
    /** Whether this attempt may still commit messages or state. */
    isCurrent(): boolean;
    /** Release the active slot if this is still the current attempt. */
    finish(): boolean;
}
/**
 * Owns the cancellation and stale-write boundary for Execute attempts.
 *
 * React state stays in `PlaygroundShell`; this small state machine keeps the
 * supersession rules independently testable and makes every invalidation path
 * use the same abort behavior.
 */
export declare class PlaygroundExecutionLifecycle {
    private active;
    private epoch;
    begin(): IPlaygroundExecutionAttempt;
    /**
     * Abort the active attempt and make its callbacks stale.
     *
     * Returns whether an active attempt was canceled.
     */
    invalidate(reason: string): boolean;
}