The auto-finish readystatechange listener registered for each pageload span in browserTracingIntegration was never removed. Since the handler closes over the idleSpan (and the rest of the route-span closure), every pageload leaked a listener and kept the span it retained alive — the growing set of Sentry functions reported in #21630.

The previous handler was an anonymous arrow function, so it could not be removed via removeEventListener. The { once: true } option suggested in the issue does not fully address the leak either: in the common case where the document is already loaded when the span starts, the listener never fires and therefore is never auto-removed.

This change passes emitFinish directly as the handler and removes it as soon as the auto-finish signal is emitted. This covers both cases:

• Document already loaded when the span starts → signal emitted synchronously, listener removed immediately.
• Document still loading → listener fires on the next readystatechange, emits, and removes itself.

Since the framework integrations (Vue, Astro, Next.js, Remix, SvelteKit, Ember) all wrap the browser package's browserTracingIntegration, this single fix covers them too.

Root cause

optionalWindowDocument.addEventListener('readystatechange', () => { emitFinish(); }) added a fresh, unremovable listener for every pageload span without ever detaching it.

Fixes #21630