/**
 * Bound version of `inner[prop]` if it is a function, cached so repeated
 * reads return the same reference. Identity matters for `{#each}` keying
 * and consumer memoization.
 *
 * @param {object | Function} inner
 * @param {string | symbol} prop
 * @param {unknown} source the freshly-read value of `inner[prop]`
 */
export function bindForwarded(inner: object | Function, prop: string | symbol, source: unknown): any;
/**
 * Build a Proxy wrapping `self` so reads forward to its inner value and
 * writes follow the chosen policy. Shared between `Box` (mutable) and
 * `ConstBox` (read-only). The caller's constructor should
 * `return buildBoxProxy(this, opts);` after `super(initial)`.
 *
 * @param {{ value: unknown } & Record<PropertyKey, unknown>} self the
 *   underlying box instance. Reads of own keys route to it; the proxy
 *   itself is returned from the constructor.
 * @param {object} [opts]
 * @param {boolean} [opts.readOnly=false] when true, every write trap
 *   throws `TypeError(opts.writeMessage)`. When false, writes route to
 *   `self` (own keys) or `self.value` (inner keys).
 * @param {Set<string|symbol>} [opts.forwardFirst] property names where
 *   the inner method should win over the box's own (e.g. `get`/`set`
 *   for `boxedMap` ergonomics).
 * @param {string} [opts.writeMessage] thrown by every write trap when
 *   `readOnly` is true.
 * @param {string} [opts.deleteOwnMessage] thrown when deleting an own
 *   helper key on a mutable box. Ignored under `readOnly`.
 * @param {string} [opts.preventExtensionsMessage] thrown by
 *   `preventExtensions` on both variants.
 * @param {string} [opts.setPrototypeOfMessage] thrown by
 *   `setPrototypeOf` on both variants.
 * @param {string} [opts.applyNonFunctionMessage] thrown by `apply` when
 *   the inner value is not a function.
 * @param {string} [opts.constructNonFunctionMessage] thrown by
 *   `construct` when the inner value is not a function.
 */
export function buildBoxProxy(self: {
    value: unknown;
} & Record<PropertyKey, unknown>, opts?: {
    readOnly?: boolean | undefined;
    forwardFirst?: Set<string | symbol> | undefined;
    writeMessage?: string | undefined;
    deleteOwnMessage?: string | undefined;
    preventExtensionsMessage?: string | undefined;
    setPrototypeOfMessage?: string | undefined;
    applyNonFunctionMessage?: string | undefined;
    constructNonFunctionMessage?: string | undefined;
}): () => void;