feat(browser): Start a navigation span for bfcache restores - #23748
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… bfcache Prototype. A bfcache restore resurrects the frozen document, so there is no document load and no usable history event: `popstate` either doesn't fire or is swallowed, because the URL is unchanged from when the page was frozen. Two independent guards in the existing path suppress it, neither written with bfcache in mind, so there is no small nudge that gets a span out of it. Without one, everything after the restore joins the trace the page had before it was frozen, separated by however long it sat in the cache. That misattributes errors, breadcrumbs, clicks and fetches, not just the web vitals that prompted this. The span is started from a `pageshow` listener in `browserTracingIntegration` rather than `bfcacheIntegration`, so it does not depend on an opt-in integration that is about hit/miss diagnostics. It is gated on `instrumentNavigation` and on by default. It carries `browser.navigation.type: bfcache`. A restore is near-instant, so without a way to filter these out they would drag navigation duration percentiles down exactly the way bfcache vitals would have dragged LCP. The span deliberately starts at the `pageshow` event rather than from `PerformanceNavigationTiming`, which is not replaced on restore and still describes the original document load. Known gap, pinned by a test: `bfcacheIntegration` registers its own `pageshow` listener from `setupOnce`, which core always runs before every `afterAllSetup`, so its hit/miss metric is emitted before this span exists and still lands on the pre-freeze trace.
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Starts a navigation span when the page is restored from the back/forward cache.
A restore resurrects the frozen document, so there is no document load and no usable history event:
popstateeither doesn't fire or is swallowed because the URL is unchanged. Without a span of its own, everything after the restore joins the trace the page had before it was frozen, which misattributes errors and breadcrumbs as much as vitals.It lives in
browserTracingIntegrationrather thanbfcacheIntegrationso it doesn't depend on an opt-in integration being enabled, and carriesbrowser.navigation.type: bfcachesince a restore is near-instant and would otherwise drag navigation duration percentiles down with no way to tell it apart.Stacked on #23425.