- Add ElementKind (Static/Dynamic) to SceneElement base; Source/WebcamSceneConfig classify
- Services/SceneGraph.cs: owns the Scenes collection (ViewModel's Scenes delegates to it),
the element mutation surface (Add/Insert/Remove/Move, each invalidating the bake), and the
queries that were scattered LINQ (GetBackground/GetWebcam/GetChatBoxes/GetSplitPoint/IsStatic)
- SceneCompositor: split-aware BakeStaticBase + CompositeLayers + Render(.., staticBase, split);
builds/caches the static base below the split point in source-rect space
- FramePump: optional SceneGraph -> optimized bake+composite path; falls back to full render
- MainViewModel: routes element mutations through the graph; invalidates the bake on static
layout/opacity/visibility/useDefaultBackground changes and after background heal/Ensure
- Integration test SceneGraphTests.BakedStaticBase_WithDynamicLayer_CompositesCorrectly
Derivative survey (mandated): tried before writing — OBS does per-source opacity/visibility
caching and static-scene baking; this mirrors OBS's 'cached static source' optimization.
3 documented defensive deviations from the spec (ChatOverlayLayer stays decoupled;
background helpers stay VM-static for direct testability; full facade peel deferred post-1.0)
in TASKS.md + ai.md. Scope check passed; clean build 0 warnings.
Core MainViewModel.cs 758 -> 495 lines. Moved the source add/remove/image
block (AddSource, NextSourceName, AddImage, BuildImageCandidates,
PickImageBytes, AddAsset, AddImageSource, AddReusedImage, RemoveElement) into a
new MainViewModel.Sources.cs partial, and WebView2 source hosting
(RegisterLoadedWebSources, InitWebView2, OnWebView2PreviewBitmapChanged) into a
new MainViewModel.Web.cs partial. Pruned now-dead usings from core.
Zero behavior change; build 0 warnings; 246 pass, only the 2 known failures.
Docs: ViewModels/index.md Phase 3 tracker updated in same commit.
gramps