/**
 * Where the compositor's words go.
 *
 * The trailer modules narrate as they work — windows scored, overlays rasterized, the render
 * summary — and under `--json` every one of those lines must land on stderr, because stdout is
 * reserved for the single result document (`output.ts`). The modules cannot know which mode the
 * command runs in, so the command binds the Output seam here first and everything below it
 * writes through `out`/`warn` without caring.
 *
 * Unbound (a test, or a module used as a library) both go to stderr: never stdout, so nothing here
 * can corrupt a result by accident.
 */
export interface TrailerLog {
    info(line: string): void;
    warn(line: string): void;
}
/** The command layer calls this once with `createOutput(json)` before running any pipeline step. */
export declare function bindTrailerLog(log: TrailerLog): void;
/** Back to stderr — for tests that bound a capturing log. */
export declare function resetTrailerLog(): void;
export declare function out(line: string): void;
export declare function warn(line: string): void;