import type { FontFaceDescriptor } from "../transport/protocol";
/**
 * Walk every accessible `@font-face` rule in the document and collect a
 * descriptor list ready for forwarding to a Web Worker, where each
 * entry is reconstituted via `new FontFace(family, src, descriptors)`
 * and registered in the worker's own `self.fonts` set.
 *
 * Background: a `Worker` has its own `FontFaceSet` distinct from the
 * document's. Fonts loaded into `document.fonts` (by `<link>`,
 * `@font-face`, or programmatic `FontFace`) are *not* visible to the
 * worker — Canvas2D `ctx.font` lookups inside the worker fall back to
 * the platform default if the family isn't in `self.fonts`. This
 * helper bridges that gap for the in-CSS case.
 *
 * # CORS / security caveats
 *
 * 1. **Cross-origin stylesheets without permissive CORS** throw
 *    `SecurityError` on `cssRules` access, and we silently skip them.
 *    Their `@font-face` rules are unreachable to JS regardless of
 *    where the worker would re-load them, so this is the same
 *    fundamental limitation the document itself has.
 *
 * 2. **Font URLs are absolutized against the parent stylesheet's
 *    `href`** before forwarding. The worker's own script URL is a
 *    Blob URL produced by `WorkerPlugin`, so relative URLs in the raw
 *    `src:` declaration would resolve against the Blob origin (i.e.
 *    fail). Callers should treat the absolute URLs as the canonical
 *    source.
 *
 * 3. **The actual font fetch issued by `face.load()` in the worker
 *    is a fresh cross-origin request from the worker scope.** The
 *    font server must respond with `Access-Control-Allow-Origin`
 *    (e.g. `*` or the page origin) and an appropriate
 *    `Access-Control-Allow-Headers` policy if any non-simple headers
 *    are involved. A "no-cors" / opaque response is *not* usable
 *    here: `FontFace.load()` rejects on opaque responses, and even
 *    if it didn't, painted glyphs would taint the canvas and break
 *    `getImageData`. Same-origin fonts (including `data:` URIs)
 *    sidestep this entirely.
 *
 * 4. **Programmatic fonts** (e.g. `document.fonts.add(new
 *    FontFace(name, source))`) are *not* captured by this walker —
 *    they don't appear in any stylesheet's `cssRules`. Iterating
 *    `document.fonts` directly would catch them, but `FontFace`
 *    instances don't expose their source URL or buffer post-
 *    construction, so there's no public path to forward them. If a
 *    test or app needs that, it must register the same fonts in the
 *    worker explicitly.
 */
export declare function snapshotFontFaces(): FontFaceDescriptor[];