Description

Fixes a possible iOS 26 bottom accessory crash during invalidation.

The helper registers KVO for center on self.nativeWrapperView, but invalidation removed the observer from _bottomAccessoryView.superview.superview at teardown time. UIKit can detach or swap the bottom accessory wrapper before invalidation runs, so the teardown path may attempt to remove the observer from a different wrapper view and raise an NSRangeException because that object was never observed.

I do not see an existing issue for this exact stack, but we observed it in production on react-native-screens 4.23.0, and the same registration/removal pattern is present on current main.

Changes

• Stores the exact native wrapper view that was registered for KVO.
• Makes registerForAccessoryFrameChanges idempotent for the same wrapper and unregisters the previous wrapper if the wrapper changes.
• Removes the observer from the stored observed wrapper during invalidation instead of resolving the current superview chain again.
• Uses a dedicated KVO context and forwards unrelated observations to super.

Test plan

• yarn install --immutable
• yarn prepare
• yarn check-types
• xcrun clang-format -i ios/tabs/bottom-accessory/RNSTabsBottomAccessoryHelper.mm
• git diff --check

Existing examples that exercise bottom accessory behavior:

• apps/src/tests/issue-tests/Test3288.tsx
• apps/src/tests/single-feature-tests/tabs/bottom-accessory-layout.tsx

I did not add a JS unit test for this because the failure is caused by UIKit/KVO object identity during native view invalidation. A meaningful automated regression test would need a native iOS XCTest harness or an iOS integration/e2e test that drives bottom accessory mount, detach, and invalidation lifecycle. This repository does not appear to have an iOS native unit-test target for library internals today.

I attempted yarn test:unit after initializing the react-navigation submodule, but the root Jest command also collects the submodule's own test suites and fails on unrelated submodule Jest setup / React version issues before exercising this native change.

Checklist

• Included code example that can be used to test this change. Existing bottom accessory examples are listed above; no new JS example was added for this native KVO lifecycle fix.
• For visual changes, included screenshots / GIFs / recordings documenting the change. N/A, no visual changes.
• For API changes, updated relevant public types. N/A, no API changes.
• Ensured that CI passes