PresentationFramework: Safer tooltip handling

[etvorun]

Summary

Port tooltip safety fix to prevent exceptions when tooltip safe-area source is disposed during hover transitions.

What changed

• Added HasValidSafeArea gate so tooltip mouse-trigger logic only uses safe area when source is still valid.
• Updated MouseHasLeftSafeArea to treat invalid/disposed safe area as absent.
• Added ConvexHull.IsValid to expose underlying source validity (!_source.IsDisposed).

Why

Tooltip handling could race with tooltip window/source teardown, leaving a stale safe-area source and causing coordinate conversion paths to throw. Validating source liveness before safe-area use prevents this failure mode.

Fixes #11462

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

This pull request adds safety checks to tooltip handling to prevent exceptions when the tooltip's safe-area source (PresentationSource) is disposed during hover transitions. The fix addresses intermittent crashes that can occur when moving the mouse near tooltip boundaries while tooltips are opening/closing.

Changes:

• Added HasValidSafeArea property that checks both SafeArea existence and source validity (!_source.IsDisposed)
• Updated tooltip mouse-trigger logic in BeginShowToolTip to use HasValidSafeArea instead of just null check
• Updated MouseHasLeftSafeArea to treat invalid/disposed safe area as if it doesn't exist
• Added ConvexHull.IsValid property to expose underlying source validity

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The IsValid property should handle the case where _source might be null to prevent potential NullReferenceException. While _source is expected to be non-null based on the constructor being called only when presentationSource is not null (line 844-905), defensive programming suggests checking for null. Consider changing to: internal bool IsValid => _source != null && !_source.IsDisposed;

Suggested change

	internal bool IsValid => !_source.IsDisposed;
	internal bool IsValid => _source != null && !_source.IsDisposed;