List_PreviewMouseMove reorders StagedScene.Elements via RemoveAt/Insert,
bypassing SceneGraph's mutation surface, but never scheduled a save — the
new z-order was lost on restart. The drop now sets _dragReordered and
EndListDrag funnels it through MainViewModel.OnSceneElementsReordered()
(InvalidateBake + ScheduleSave, same background-save path as every other
mutation). Integration test (RealApp + temp DB) reproduces the exact
code-behind mutation and asserts the debounced save lands the new Source
SortOrder. Derivation reference: standard WPF ItemsControl drag-reorder
pattern (OBS layering semantics: bottom-most layer = index 0).
LeftPanel.xaml(.cs) takes the Row 1 Col 0 panel (layers + properties editor and
the live chat list). All property-editor/chat handlers moved into the control
(SourceNameBox edit, AddSourceButton menu, chat autoscroll self-subscribed on
Loaded, mirror/clip-shape, remove-source, background capture change/refresh,
opacity slider label, list drag-to-reorder, snapshot revert/accept family).
Window keeps only shell + routing: ctor wiring (_leftPanel), geometry, hotkeys,
taskbar overlay, BackToAbout, Window_PreviewMouseLeftButtonDown (uses
_leftPanel.IsClickInside), UpdateSelectionOverlay (calls _leftPanel.OnSelectionChanged).
Zero behavior change; build 0 warnings; 246 pass, only the 2 known failures.
Docs: ViewModels/index.md Phase 2 tracker updated in same commit.
gramps