/**
 * The frame resize protocol — ONE implementation, both frames.
 *
 * Every Vendo iframe (the served app's http frame, the box app template) lets a
 * document the host cannot see report its own natural height. The identity gate
 * is the security half of that, and a second copy of a security gate is a
 * second gate to get wrong — so the gate, the message validation, and the clamp
 * live here and nowhere else.
 *
 * The wire: the framed document posts `{ vendo: true, kind: "resize", height }`
 * to its parent (`postToHost` in embedded-runtime.ts stamps every message), and
 * the host fits the frame to it.
 */
/**
 * The ceiling a host that configures nothing gets, kept to the pixel so no
 * shipped host's behaviour changes.
 */
export declare const DEFAULT_FRAME_MAX_HEIGHT = 8192;
/**
 * The identity gate. `event.source` is the window that actually sent the
 * message, and it is the one thing a sender cannot forge — only the frame we
 * rendered may speak for that frame. Every other window (the host page, another
 * embed, an ad frame, an opener) is ignored in silence.
 */
export declare function isFromFrame(frame: HTMLIFrameElement | null, event: MessageEvent): boolean;
/**
 * The one resize handler both frames install: identity gate, then validation,
 * then the host's bounds, then apply. Returns whether the frame was resized, so
 * a caller with other message kinds can use it as an arm of its own chain.
 */
export declare function applyFrameResize(frame: HTMLIFrameElement | null, event: MessageEvent): boolean;
/**
 * The ceiling declaration both frames carry. It is load-bearing CSS (the browser
 * enforces it whatever height we write) and it is what `clampToHostBounds` reads
 * back, so the host has exactly one place to change: the custom property.
 */
export declare const FRAME_MAX_HEIGHT_CSS = "var(--vendo-app-frame-max-height, 8192px)";