/**
 * Shared source-evaluator contract.
 *
 * Every source module exports `evaluate(source)` (the poll model — one snapshot,
 * or null when nothing is observable this tick / the source is push-only) and,
 * where push-based (ws, file-follow), a `subscribe(source, onObs)` returning an
 * unsubscribe fn.
 */
export {};
