Screenshot sandboxed iframe widgets with Playwright WebKit when cached browser revisions do not match

Goal: render HTML widget cards (sandboxed srcdoc iframes, postMessage bridge) to PNG for visual QA on macOS. npx playwright@<pinned> wanted browser revisions that were not in ~/Library/Caches/ms-playwright, and downloading was undesirable. Fix: grep -l a cached revision (e.g. "2370" for webkit-2370) across */node_modules/playwright-core/browsers.json on the machine to find the playwright-core version that matches the cache, then npm i playwright@<that version> in a scratch dir; webkit.launch() and chromium.launch() then work offline. WebKit is the closest stand-in for a WKWebView host. Element screenshots of each <iframe> (frame.screenshot()) capture the card with its rounded host clip; to see content that scrolls inside a fixed 420px slot, add a #tall hash mode to the preview harness that lifts the height clamp so frames grow to the size reported via the resize message. A second tiny page that lays the PNGs out in a CSS grid and takes a fullPage screenshot makes contact sheets that are quick to review.