Precision gap: self-owned-template-part exemption doesn't cover a local-variable/pattern-match capture

[PhysShell]

Found by: the issue #201 oracle sweep, docs/notes/oracle-sweep-2026-07-10.md; catalogued as docs/notes/field-notes-patterns.md entry 16.

The pattern

A named template part (GetTemplateChild/Template.FindName) is owned by the control's own template — its lifetime is bound to the control instance, the exact shape the shipped self-owned-template-part exemption already covers (docs/notes/real-world-mining.md's GetTemplateChild/FindName fix). That fix keys off a field assignment (_field = GetTemplateChild(...) as T); both examples below store the template part in a local instead.

// MahApps.Metro, MetroWindow.cs:1447-1449
if (this.GetTemplateChild(PART_Content) is MetroContentControl metroContentControl)
{
 metroContentControl.TransitionCompleted += (_, _) => this.RaiseEvent(...); // <- flagged
}

// AvalonEdit, OverloadViewer.cs:58-64
public override void OnApplyTemplate() {
 base.OnApplyTemplate();
 Button upButton = (Button)this.Template.FindName("PART_UP", this);
 upButton.Click += (sender, e) => { ... }; // <- flagged
 Button downButton = (Button)this.Template.FindName("PART_DOWN", this);
 downButton.Click += (sender, e) => { ... }; // <- flagged
}

Evidence — confirmed in 2 separate repos

• MahApps.Metro src/MahApps.Metro/Controls/MetroWindow.cs:1447-1449 (an is T x pattern-match local)
• AvalonEdit ICSharpCode.AvalonEdit/CodeCompletion/OverloadViewer.cs:58,64 (a plain local variable, via FindName rather than GetTemplateChild)

Suggested direction (not prescriptive)

Extend the self-owned-template-part exemption's recognition from "assigned to a field" to "the result of GetTemplateChild/Template.FindName, however it's captured" — a plain local, an is T x pattern variable, or a field, all equally template-owned.

Scope

No analyzer code changed as part of the sweep — this issue tracks the fix as its own unit of work.