fix: Prevent region orphaning during Hot Reload in ReassignParent

[Copilot]

GitHub Issue (If applicable): closes #2912

PR Type

What kind of change does this PR introduce?

• Bugfix

What is the current behavior?

Re-adding a Button Command binding via Hot Reload breaks TabBar navigation. After Hot Reload, tapping a tab does nothing because the region becomes orphaned:

1. ReassignParent() unconditionally sets Parent = null
2. AssignParent() may return early if View.GetAttached() is false during Hot Reload timing
3. Region left with Parent = null, _services = null
4. Region.Navigator() returns null, navigation fails

What is the new behavior?

ReassignParent() now preserves parent relationship when reassignment would fail:

• Precondition check: Returns early if View is null, is root, or not attached
• Find-before-clear: Locates new parent before modifying current state
• Preserve existing: Keeps current parent if no new parent found (prevents orphaning)
• Atomic update: Sets parent and name together when new parent exists

// Before: unconditionally orphans, then tries to recover
Parent = null;
AssignParent();

// After: only changes parent when safe
var newParent = View.FindParentRegion(out var routeName);
if (newParent is null && Parent is not null)
    return; // Keep existing parent
if (newParent is not null)
{
    Parent = newParent;
    Name = routeName;
}

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Docs have been added/updated which fit documentation template. (for bug fixes / features)
• Unit Tests and/or UI Tests for the changes have been added (for bug fixes / features) (if applicable)
• Wasm UI Tests are not showing unexpected any differences. Validate PR Screenshots Compare Test Run results.
• Contains NO breaking changes
• Updated the Release Notes
• Associated with an issue (GitHub or internal)

Other information

Hot Design works because it preserves element identity during updates. Hot Reload may trigger AttachedChanged → ReassignParent() with timing where GetAttached() temporarily returns false.

Internal Issue (If applicable):

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>[HR][Gaps][Navigation/MVUX] Re-adding Button Command binding breaks Tabbar navigation</issue_title>
<issue_description><!-- Please use this template while reporting a bug and provide as much info as possible. Not doing so may result in your bug not being addressed in a timely manner. Thanks!

If the matter is security related, please disclose it privately via https://github.com/nventive/Uno/security/
-->

Current behavior

• Re-adding a command binding via Hot Reload breaks Shell/TabBar tab switching (can’t return to previous tab). Affects any app using TabBar/NavigationView to drive regions;

• Doing the same using HD works.

Untitled.video.-.Made.with.Clipchamp.mp4

Expected behavior

How to reproduce it (as minimally and precisely as possible)

Repro using the Chefs app: (https://github.com/unoplatform/uno.chefs/blob/f8c5943efa4eb702a066d09c6e3ef389ade3b973/Chefs/Views/HomePage.xaml#L99)

1. On HomePage, remove Command="{Binding ShowAll}" from the “View all” button; run.

2. Re-add the command and apply Hot Reload.

3. Tap View all → navigates to /Main/-/Search.

4. Tap Home tab.

5. Home tab does nothing (stays on Search). Doing the same flow with Hot Design works.

Environment

Nuget Package (s):

Package Version(s):

Affected platform(s):

• iOS
• macOS (AppKit)
• Mac Catalyst
• Android
• WebAssembly
• Windows
• Skia (WPF)
• Skia (GTK on Linux/macOS/Windows)
• Skia (Linux Framebuffer)
• Build tasks

Visual Studio:

• 2019 (version: )
• 2022 (version: )
• Visual Studio Code (version: )
• Rider Windows (version: )
• Rider macOS (version: )

Relevant plugins:

• Resharper (version: )

Anything else we need to know?

</issue_description>

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

• Fixes [HR][Gaps][Navigation/MVUX] Re-adding Button Command binding breaks Tabbar navigation #2912

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