fix: NavigationView compact pane PaneItemExpander flyout size and position

[Copilot]

In RTL directionality, the compact navigation pane appears on the physical right side of the screen. The flyout was hardcoded to FlyoutPlacementMode.rightTop, which only had ~50px of available space (the pane width itself) rather than the full content area width. Additionally, the leftTop/rightTop flyout placement modes had a vertical positioning bug that caused flyouts to appear in the middle of the screen instead of aligned with the target item.

Changes

• pane_items.dart: Resolve the flyout placement mode against the current text direction so it uses leftTop in RTL (physically left = into the content area) and rightTop in LTR — leveraging the existing FlyoutPlacementMode.resolve() method.

// Before
placementMode: displayMode == PaneDisplayMode.compact
    ? FlyoutPlacementMode.rightTop
    : FlyoutPlacementMode.bottomCenter,

// After
final textDirection = Directionality.of(context);
placementMode: displayMode == PaneDisplayMode.compact
    ? FlyoutPlacementMode.rightTop.resolve(textDirection)
    : FlyoutPlacementMode.bottomCenter,

• flyout.dart: Fixed horizontalTopY calculation in _FlyoutPositionDelegate. The old formula used two chained clampVertical calls that produced incorrect results when the flyout is taller than the space above the target element, causing the flyout to appear in the middle of the screen:

// Before - wrong when flyout height exceeds space above target:
final topY = clampVertical(targetOffset.dy - targetSize.height - flyoutSize.height);
final horizontalTopY = clampVertical(topY + flyoutSize.height);

// After - directly computes the top edge of the target element:
final horizontalTopY = clampVertical(targetOffset.dy - targetSize.height);

• test/navigation_view_test.dart: Added regression test asserting the flyout width exceeds kCompactNavigationPaneWidth when opened in RTL compact mode.
• CHANGELOG.md: Added entries under 4.15.0.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>🐛 NavigationView compact pane Flyout is too small when in right-to-left directionality</issue_title>
<issue_description>To Reproduce
Steps to reproduce the behavior:

1. Set directionality to right-to-left
2. Set navigation view pane to compact mode
3. Add a PaneItemExpander and children
4. Press pane item expander on the sidebar.

Expected behavior
Same as left-to-right.

Screenshots

Additional context
n/a
</issue_description>

<agent_instructions>Update the tests and update the changelog at the end.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes 🐛 NavigationView compact pane Flyout is too small when in right-to-left directionality #1289

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[bdlukaa]

@copilot The first PaneItemExpander of the home screen is being displayed at the middle of the screen. It should be positioned correctly.

[Copilot]

@copilot The first PaneItemExpander of the home screen is being displayed at the middle of the screen. It should be positioned correctly.

Fixed in d2a9f35. The root cause was a bug in _FlyoutPositionDelegate.getPositionForChild in flyout.dart. The horizontalTopY variable (used for leftTop/rightTop placement) was computed via two chained clampVertical calls:

// Old - wrong when flyout is taller than space above the target:
final topY = clampVertical(targetOffset.dy - targetSize.height - flyoutSize.height);
final horizontalTopY = clampVertical(topY + flyoutSize.height);

When topY gets clamped to margin (item near the top, tall flyout), horizontalTopY becomes margin + flyoutSize.height — placing the flyout far too low.

// New - directly computes the top edge of the target:
final horizontalTopY = clampVertical(targetOffset.dy - targetSize.height);

This correctly aligns the flyout's top edge with the top of the target element in all cases.