[0.82.0] Different behavior of views with position: "absolute" between old and new architecture

Description

In the old React Native architecture, a view with position: "absolute" will overlap a child of its sibling even if that child had a higher zIndex. This meant that box1 (blue) appears below box2 (red):

In the new architecture, the stacking behavior is different — box2, being absolutely positioned outside the sibling hierarchy, will overlap box1:

Steps to reproduce

1. Build and run rn-tester.
2. Open RNTesterPlayground.js with reproducer.

React Native Version

0.82.0

Affected Platforms

Runtime - Android, Runtime - iOS

Areas

Fabric - The New Renderer

Output of npx @react-native-community/cli info

info Fetching system and libraries information...
System:
  OS: macOS 15.4.1
  CPU: (12) arm64 Apple M3 Pro
  Memory: 164.56 MB / 18.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.17.1
    path: /Users/wojciechloboda/.nvm/versions/node/v22.17.1/bin/node
  Yarn:
    version: 1.22.22
    path: /opt/homebrew/bin/yarn
  npm:
    version: 10.9.2
    path: /Users/wojciechloboda/.nvm/versions/node/v22.17.1/bin/npm
  Watchman:
    version: 2025.04.28.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /opt/homebrew/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.5
      - iOS 18.5
      - macOS 15.5
      - tvOS 18.5
      - visionOS 2.5
      - watchOS 11.5
  Android SDK:
    API Levels:
      - "28"
      - "31"
      - "33"
      - "35"
      - "36"
    Build Tools:
      - 28.0.3
      - 30.0.2
      - 30.0.3
      - 34.0.0
      - 35.0.0
      - 35.0.1
      - 36.0.0
      - 36.0.0
    System Images:
      - android-33 | Google Play ARM 64 v8a
      - android-35 | Google Play ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2024.2 AI-242.23726.103.2422.12816248
  Xcode:
    version: 16.4/16F6
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.15
    path: /opt/homebrew/opt/openjdk@17/bin/javac
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.0.0
    wanted: 20.0.0
  react:
    installed: 19.1.1
    wanted: 19.1.1
  react-native:
    installed: 0.82.0
    wanted: 0.82.0
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: Not found
  newArchEnabled: false

Stacktrace or Logs

.

MANDATORY Reproducer

https://github.com/facebook/react-native/pull/54169

Screenshots and Videos

Old arch:

New arch:

Build and run rn-tester, then open RNTesterPlayground.js with the reproducer linked in PR 54169. Compare absolute-position and zIndex stacking under the old and new architectures on Android and iOS; done means the behavior is consistent with the expected sibling hierarchy in both architectures.