/**
 * Deferred one-shot open for hosts that may not have a real size yet.
 *
 * xterm's `Terminal.open()` must not run in a zero-size container: the
 * renderer creation fails there (the DomRenderer is built from the host's
 * dimensions), leaving the render service's renderer `undefined`, and the
 * next Viewport refresh crashes reading `.dimensions` off it. WebKit-based
 * hosts (WKWebView) reliably report zero while the bottom panel's expand
 * slide is in flight; any `display:none`-hidden ancestor does the same.
 *
 * The caller's `open` callback (open + fit + resize) is invoked exactly
 * once, on the first frame where the host reports a real size. While the
 * host stays zero-sized the polling continues every frame; it stops when
 * the host leaves the document (`isConnected`), so a pending open never
 * fires after unmount. The returned cancel function drops a pending frame
 * immediately (idempotent).
 *
 * `raf`/`caf` are injectable so tests can drive the polling deterministically.
 */
export declare function openWhenSized(host: HTMLElement, open: () => void, raf?: (cb: FrameRequestCallback) => number, caf?: (id: number) => void): () => void;