[PresentationFramework] Tooltip safe-area handling can throw during hover transitions

[etvorun]

[PresentationFramework] Tooltip safe-area handling can throw during hover transitions

Summary

Tooltip processing can throw when pointer movement intersects with a tooltip whose underlying window/source is disposed during hover transitions.

Observed behavior

• In tooltip-heavy UI paths, moving the mouse near or over tooltip boundaries can trigger an exception in tooltip coordinate processing.
• The failure is intermittent and timing-sensitive, so it can be difficult to reproduce deterministically.

Repro notes

1. Run a WPF app with controls that frequently show/hide tooltips.
2. Move the mouse quickly across controls while tooltips are opening/closing.
3. Observe occasional exceptions originating from tooltip safe-area coordinate conversion paths.

Impact

• This can crash or destabilize applications during normal tooltip interaction.
• Apps with dense UI surfaces and frequent tooltip activity are more likely to be affected.

Expected behavior

Tooltip transitions should remain safe even if the tooltip's underlying source/window is disposed mid-flow.

Actual behavior

The tooltip path may still use a previously captured safe-area source that has already been disposed, causing coordinate conversion to fail and throw.

Suspected root cause

Safe-area checks only validated presence (SafeArea != null) and did not validate whether the underlying PresentationSource was still alive when used.

Proposed fix direction

• Introduce a validity gate for safe-area usage, not just null checks.
• Treat disposed safe-area sources as invalid and fall back to behavior equivalent to "no safe area".
• Route tooltip mouse-trigger logic and safe-area exit checks through the new validity gate.
• Expose convex hull/source validity in a minimal internal property used by tooltip logic.