[Android][Fabric] Screen.fragmentWrapper retains destroyed ScreenFragment via Fabric's mTagToViewState

Description

On Android with Fabric (New Architecture), destroyed ScreenStackFragment / ScreenFragment instances are retained in memory because Screen.fragmentWrapper is never nulled after the fragment receives onDestroy().

Fabric's SurfaceMountingManager.mTagToViewState keeps Screen and ScreenContainer views alive as long as their surface is mounted — this is normal Fabric behavior. But because Screen.fragmentWrapper still points to the destroyed fragment, that fragment (and everything it retains) can never be GC'd.

This is a separate leak path from ScreenDummyLayoutHelper (#3636), but both stem from the same root cause: references not being cleaned up after Activity/Fragment destruction.

Leak traces (LeakCanary 2.14)

Trace 1 — ScreenContainer.parentScreenWrapper → ScreenStackFragment

┬───
│ GC Root: Global variable in native code
│
├─ com.facebook.react.fabric.FabricUIManager instance
│    Leaking: NO (ScreenContainer↓ is not leaking)
│    ↓ FabricUIManager.mMountingManager
├─ com.facebook.react.fabric.mounting.MountingManager instance
│    ↓ MountingManager.mostRecentSurfaceMountingManager
├─ com.facebook.react.fabric.mounting.SurfaceMountingManager instance
│    ↓ SurfaceMountingManager.mTagToViewState
├─ java.util.concurrent.ConcurrentHashMap instance
├─ SurfaceMountingManager$ViewState instance
│    ↓ SurfaceMountingManager$ViewState.mView
├─ com.swmansion.rnscreens.ScreenContainer instance
│    Leaking: NO (View attached)
│    ↓ ScreenContainer.parentScreenWrapper
│                      ~~~~~~~~~~~~~~~~~~~
╰→ com.swmansion.rnscreens.ScreenStackFragment instance
     Leaking: YES (Fragment#onDestroy() callback received)
     Retaining 941 B in 27 objects

Trace 2 — Screen.fragmentWrapper → ScreenFragment

┬───
│ GC Root: Global variable in native code
│
├─ com.facebook.react.fabric.FabricUIManager instance
│    ↓ FabricUIManager.mMountingManager
├─ MountingManager instance
│    ↓ MountingManager.mostRecentSurfaceMountingManager
├─ SurfaceMountingManager instance
│    ↓ SurfaceMountingManager.mTagToViewState
├─ ConcurrentHashMap instance
├─ SurfaceMountingManager$ViewState instance
│    ↓ SurfaceMountingManager$ViewState.mView
├─ com.swmansion.rnscreens.Screen instance
│    Leaking: NO (View attached)
│    ↓ Screen.fragmentWrapper
│             ~~~~~~~~~~~~~~~
╰→ com.swmansion.rnscreens.ScreenFragment instance
     Leaking: YES (Fragment#onDestroy() callback received)
     Retaining 855 B in 26 objects

Root cause

Screen.fragmentWrapper (Screen.kt#L57) is set when a fragment is created but never nulled on fragment destruction.

Meanwhile, ScreenContainer.parentScreenWrapper is properly nulled in onDetachedFromWindow() (ScreenContainer.kt#L290), showing the intended cleanup pattern already exists in the codebase — it was just not applied to Screen.fragmentWrapper.

Suggested fix

Null out screen.fragmentWrapper in ScreenFragment.onDestroy():

// ScreenFragment.kt — onDestroy()
override fun onDestroy() {
    super.onDestroy()
    // ... existing code ...
    childScreenContainers.clear()
    screen.fragmentWrapper = null  // break the retention chain
}

Environment

• react-native-screens: 4.20.0 (also confirmed unpatched on main as of 4.24.0)
• React Native: 0.81 (Fabric / New Architecture enabled)
• Android: API 29 (Samsung Galaxy A7)
• LeakCanary: 2.14