iOS: safeAreaInsets not propagated to child UIKit views — contentInsetAdjustmentBehavior broken

[IsaacIsrael]

Bug

contentInsetAdjustmentBehavior has no effect on UIScrollView instances (including FlashList / FlatList) embedded inside PagerView pages. Scroll views report safeAreaInsets = .zero, so they cannot automatically adjust content insets for overlapping system chrome (e.g. translucent tab bars on iOS 26 liquid glass).

Environment

• react-native-pager-view: 8.0.0
• React Native: 0.78
• iOS: 26 (liquid glass translucent tab bar with drawBehind: true)
• Architecture: New Architecture (Fabric)

Steps to reproduce

1. Use a bottom tab navigator with drawBehind: true and a translucent tab bar (iOS 26 liquid glass)
2. Place a PagerView inside a tab screen
3. Add a scrollable list (e.g. FlashList or FlatList) inside a PagerView page
4. Set contentInsetAdjustmentBehavior='scrollableAxes' on the scroll view
5. Scroll to the bottom of the list

Expected: Last item stops above the tab bar (scroll view adds ~83pt bottom content inset automatically)

Actual: Last items are hidden behind the tab bar. The scroll view's adjustedContentInset.bottom remains 0.

Root cause

The UIHostingController is initialized with ignoreSafeArea: true (PagerViewProvider.swift L109-111), which calls disableSafeArea() and dynamically subclasses the hosting view to override safeAreaInsets → .zero.

Even without ignoreSafeArea, RepresentableView uses UIViewRepresentable which embeds a plain wrapper UIView. SwiftUI does not propagate safe area insets through UIViewRepresentable — the wrapper and all its descendant UIKit views see safeAreaInsets = .zero.

Debug log evidence (added print statements to trace the view hierarchy):

HostingController.view.safeAreaInsets: bottom: 83     ← correct at hosting level
PagingCollectionView.safeAreaInsets:   bottom: 83     ← correct at TabView collection
Wrapper UIView.safeAreaInsets:         bottom: 0      ← LOST HERE (UIViewRepresentable boundary)
RCTEnhancedScrollView.safeAreaInsets:  bottom: 0      ← zero → contentInsetAdjustmentBehavior noop
  contentInsetAdjustmentBehavior: 2 (scrollableAxes)
  adjustedContentInset: bottom: 0                     ← no adjustment despite scrollableAxes

Proposed fix

PR #1085 addresses this with three changes:

1. Replace UIViewRepresentable → UIViewControllerRepresentable with a PageChildViewController that reads the hosting view's real safeAreaInsets and re-injects them via additionalSafeAreaInsets
2. Add .ignoresSafeArea() to the SwiftUI TabView body so pages extend behind system chrome
3. Remove ignoreSafeArea: true from UIHostingController init so the hosting view preserves real insets