Break the reference chain so old containers can be garbage collected.

[gpaskaleva-msft]

Fixes #11337

Description

ElementProxy.cs:

• _peer made non-readonly + ClearPeer() method — allows DisconnectPeerFromUia to sever the strong proxy → peer reference immediately (for non-UIElement peers like DataGridItemAutomationPeer)

AutomationPeer.cs:

1. EnsureChildren() disconnect logic — detects removed peers when _children is refreshed during UIA traversal and calls DisconnectPeerFromUia on them.
2. DisconnectPeerFromUia changes:

• proxy.ClearPeer() — severs proxy→peer strong reference
• Dispatcher.BeginInvoke for UiaDisconnectProvider — defers COM disconnect to outside UIA callback context
• peer._children = null; peer._childrenValid = false; — the critical fix that breaks the chain from disconnected peer → cached cell peers → old DataGridCell/Row containers

Regression

No

Testing

Test Environment

• Repro app (WPFUI): DataGrid with 200k rows, ItemsSource rebound every 3 seconds
• UIA client (WPFAutomationClient): Calls FindAll(TreeScope.Descendants, TrueCondition) every 1 second
• Runtime: Custom-built PresentationCore.dll deployed to local .NET 11 Preview 5 SDK

Tests Performed

#	Fix Applied	Result	Duration
1	PR #11657 only (EnsureChildren disconnect)	❌ Memory grew to ~2500 MB	20 min
2	+ ClearPeer() on ElementProxy	❌ No improvement	~5 min
3	+ Deferred UiaDisconnectProvider via Dispatcher.BeginInvoke	❌ Still ~6-9 MB/cycle growth	~5 min
4	+ Diagnostic counters (verified disconnects fire: 45/cycle, refreshes accelerating)	❌ 911→1019 MB in 14 cycles	~1 min
5	+ peer._children = null; peer._childrenValid = false; in DisconnectPeerFromUia	✅ Stable 449-534 MB	3+ min

Risk

Microsoft Reviewers: Open in CodeFlow

[amarinov-msft]

The changes are looking good. We just need to merge #11723 here before merging this PR.

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[Copilot]

Pull request overview

Fixes a UI Automation-related memory leak in WPF by ensuring stale AutomationPeer instances (and their cached child-peer graphs) are actively disconnected from UIA and have their strong reference chains broken, allowing old/recycled containers to be garbage collected.

Changes:

• Adds stale-child detection to EnsureChildren() and disconnects removed peers during UIA traversal refreshes.
• Introduces DisconnectPeerFromUia() to clear proxy→peer references, defer UiaDisconnectProvider outside UIA callback context, and sever peer→children chains.
• Updates ElementProxy to allow clearing its peer reference via a new ClearPeer() method.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Automation/Peers/AutomationPeer.cs	Adds disconnect logic during child refresh, introduces deferred UIA disconnect helper, and breaks peer reference chains to enable GC.
src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/Automation/ElementProxy.cs	Makes _peer mutable and adds ClearPeer() to sever proxy→peer strong references during disconnect.

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[h3xds1nz]

Not gonna lie, this adds quite some overhead to already massively heavy invocation this recursive method call is.