Add null safety to RootComponentView() to prevent crash during island…

[gmacmaster]

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[greptile-apps]

Greptile Summary

This PR adds null safety to RootComponentView() by changing its return type from a reference to a pointer and guarding every call site with a null check, preventing a crash when m_wkRootView has already been released (e.g. during island teardown). All 17 call sites in CompositionEventHandler.cpp and the header declaration are updated consistently.

Confidence Score: 5/5

Safe to merge — the fix is minimal, targeted, and all call sites are consistently guarded.

Every use of RootComponentView() is now null-checked before dereference. The change is mechanical and consistent across all 17 sites, with no new logic or regressions introduced. No custom rules are violated.

No files require special attention.

Important Files Changed

Filename	Overview
vnext/Microsoft.ReactNative/Fabric/Composition/CompositionEventHandler.cpp	Return type changed to pointer; all 17 call sites updated with null guards (early return / break) before any dereference — consistent and complete.
vnext/Microsoft.ReactNative/Fabric/Composition/CompositionEventHandler.h	Header declaration updated from reference to pointer return type, matching the implementation change.

Sequence Diagram

sequenceDiagram
    participant EH as CompositionEventHandler
    participant RCV as RootComponentView()
    participant Island as ReactNativeIsland (weak ref)
    participant RCVObj as RootComponentView object

    EH->>RCV: call RootComponentView()
    RCV->>Island: m_wkRootView.get() (promote weak ref)
    alt island is null (already released)
        RCV-->>EH: return nullptr
        EH-->>EH: early return / break (no crash)
    else island alive
        Island->>RCVObj: GetComponentView()
        RCVObj-->>RCV: raw pointer
        RCV-->>EH: return pointer
        EH->>RCVObj: dereference (GetFocusedComponent / hitTest / etc.)
    end

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