The gate a user sees when a Chrome Built-in AI capability exists but its on-device model has not been fetched yet. Chrome refuses to start the model download outside a user activation, so the button is the only way to trigger it. Renders the download prompt, in-flight progress, the failed-attempt message, and the terminal unsupported / cannot-run-here states; returns null once the model is available. Includes ChromeAIReadyBadge. Presentational — bind availability/progress to a provider-fallback hook and pass its download action as onDownload.