Bug Description

I just discovered that the onLCP callback from web-vitals.js never runs on Safari. This causes detect.js to await indefinitely here:

And the URL Metric data is never submitted to be stored. The issue isn't specific to web-vitals.js either. I never get any console logging for the following either:

const observer = new PerformanceObserver((list) => {
	const entries = list.getEntries();
	const lastEntry = entries[entries.length - 1]; // Use the latest LCP candidate
	console.log("LCP:", lastEntry.startTime, lastEntry);
});
observer.observe({ type: "largest-contentful-paint", buffered: true });

I'm testing in Safari 18.3 on MacOS 15.3.1.