Make MainWindow partial and add a XAML skeleton with named hosts (MenuHost, ContentGrid, StatusHost, OverlayHost). Replace BuildRoot/AssignContent/ResolveControls with InitializeComponent plus imperative population of the named hosts; existing menu/sensor/plot/overlay builders are unchanged so later sub-steps can replace each region declaratively.
Bind OverlayHost.Visibility to HardwareLoadingVisibility so the empty host does not intercept hit-testing once loading completes. Builders that previously assigned via the brittle Children[] casting now use out params.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
JMR-devandCopilot
0db7de801a