Summary

Prevents stale App Router popstate completions from restoring an old history scroll position after rapid back/forward races.

Problem

window.__VINEXT_RSC_NAVIGATE__ is invoked for every popstate, and we currently run restorePopstateScrollPosition(event.state) in .finally unconditionally. If multiple back/forward traversals run concurrently, an older navigation can resolve after a newer one and incorrectly restore scroll for the stale history entry.

This manifests as jumpy/incorrect scroll when users navigate quickly or under network jitter.

Why this change is meaningful

This is not speculative UI behavior tuning; it is a concrete race-condition fix affecting user-visible navigation state:

• it changes externally observable behavior (scroll restoration correctness)
• it closes a stale async completion window
• it aligns with existing vinext nav lifecycle semantics (activeNavigationId / isCurrentNavigation) and with Next.js intent to drop superseded traversals

Implementation

In packages/vinext/src/server/app-browser-entry.ts:

• capture the navigate session id (navId) for each popstate-triggered RSC navigation via browserNavigationController.getActiveNavigationId()
• skip scroll restoration in the .finally handler unless that navId is still current
• keep the existing __VINEXT_RSC_PENDING__ identity guard for clearing only the current pending marker

Net effect: only the winner traversal may restore scroll, and superseded traversals settle quietly.

Next.js parity / reference

• Next.js App Router uses an action queue where ACTION_NAVIGATE/ACTION_RESTORE supersede pending work by marking it discarded:
  https://github.com/vercel/next.js/blob/canary/packages/next/src/client/components/app-router-instance.ts#L173-L206
• App Router popstate dispatches restore actions through this queue:
  https://github.com/vercel/next.js/blob/canary/packages/next/src/client/components/app-router.tsx#L375-L399
• Next.js Pages Router cancellation path for superseded async navigation also uses explicit cancellation handlers:
  https://github.com/vercel/next.js/blob/canary/packages/next/src/shared/lib/router/router.ts#L670-L696

Validation

• Implemented as a focused diff in the App Router popstate finalizer in the browser entry.
• Commit hash: 0abbf083