Bug: NavigationView element properties not settable via record with-expression

[sundaramramaswamy]

Problem

NavigationViewElement doesn't expose SelectedTag and IsPaneOpen as record properties, so they can't be used with with {} syntax. Agents must use .Set(nv => nv.IsPaneOpen = true) which is less discoverable.

Evidence

• settings-hub benchmark: agent tried with { SelectedTag = ..., IsPaneOpen = true } which doesn't compile

Proposed Fix

Add SelectedTag and IsPaneOpen as properties on the NavigationViewElement record, handled in the reconciler update path.

Category

Framework bug — code change + reconciler update.

[sundaramramaswamy]

Not a bug — SelectedTag, IsPaneOpen, and PaneDisplayMode are already init-only record properties on NavigationViewElement (see Element.cs:2237-2240). The with { } syntax works correctly. The benchmark agent was confused by OTHER properties that aren't init-only (like IsPaneToggleButtonVisible) which do require .Set(). The NavigationView recipe added in PR #290 clarifies this.