/**
 * One process-wide supervisor for every live eval child, forked or spawned,
 * instead of listeners per child: under `-n 10`, or an optimizer scoring a
 * whole candidate at once, per-child listeners passed ten and Node's
 * MaxListenersExceededWarning printed into the status board.
 *
 * Signals are forwarded to every live child; the listeners exist only while
 * a child is live, so an idle process keeps default handling. The first
 * terminating signal is forwarded and the children get to settle (`eval run`
 * folds the interrupted test into the run directory). A second one is the
 * user asking to force quit: every child is killed with SIGKILL and the
 * process exits with the signal's conventional code, immediately. Exiting
 * that way instead of restoring default handling matters for spawned
 * command trees: they are detached, so nothing but this supervisor reaches
 * them, and a default signal death runs no `exit` hook to reap them.
 *
 * Any exit (normal, crash, uncaught throw) reaps live children with SIGKILL.
 * The one hole no supervisor can close is SIGKILL of this process; a
 * spawned tree's remaining protection is EPIPE on its next write to our
 * closed pipes, and forked children carry a disconnect watchdog.
 */
export type ChildKill = (signal: NodeJS.Signals) => void;
/** The slice of `process` the supervisor uses; tests pass a stand-in. */
export type SupervisedProcess = {
    on(event: string, listener: (...args: any[]) => void): unknown;
    removeListener(event: string, listener: (...args: any[]) => void): unknown;
    exit(code: number): never;
};
export declare function makeChildSupervisor(proc: SupervisedProcess): (kill: ChildKill) => () => void;
/** Supervise a child until the returned function is called (on settle). */
export declare const supervise: (kill: ChildKill) => () => void;