fix(lib): stop re-subscribing global error listeners on every render

[abhay-codes07]

Problem

ErrorTrackingProvider is mounted at the root of the app (app/layout.tsx) and installs global window "error" and "unhandledrejection" listeners in an effect keyed on trackError:

const { trackError } = useErrorTracking()

useEffect(() => {
  const handleError = (event: ErrorEvent) => trackError(event.error, { ... })
  const handleUnhandledRejection = (event: PromiseRejectionEvent) => trackError(event.reason, { ... })
  window.addEventListener("error", handleError)
  window.addEventListener("unhandledrejection", handleUnhandledRejection)
  return () => { /* remove both */ }
}, [trackError])

useErrorTracking returns a fresh trackError on every render (it is a plain closure over posthog, session and pathname, not memoized), so the dependency changes every render. That tears down and re-adds both global listeners on every render of a provider that wraps the entire app, including on each navigation and session refresh. It is wasted work on a hot path, and it leaves a small window on each cycle where a synchronously thrown error can land between the removeEventListener and the following addEventListener.

Fix

Keep the latest trackError in a ref and register the listeners once for the provider's lifetime, dispatching through the ref:

const trackErrorRef = useRef(trackError)
useEffect(() => { trackErrorRef.current = trackError }, [trackError])

useEffect(() => {
  const handleError = (event: ErrorEvent) => trackErrorRef.current(event.error, { ... })
  const handleUnhandledRejection = (event: PromiseRejectionEvent) => trackErrorRef.current(event.reason, { ... })
  window.addEventListener("error", handleError)
  window.addEventListener("unhandledrejection", handleUnhandledRejection)
  return () => { /* remove both */ }
}, [])

The listeners are now added once and removed on unmount, and each report still reads the current posthog / session / pathname context through the ref. No functional change to what gets tracked, just no more churn.

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