refactor(editor): neutralize render surface handoff

docs/plan/editor-core-refactor-plan.md

@@ -41,7 +41,8 @@ incomplete:
 - Feature panels no longer use `Composition/EditorContext.h` directly, but the
   app include surface still needs to be narrowed before this boundary is
   build-enforced.
-- Win32 and D3D12 currently know about each other through concrete headers.
+- The direct Win32/D3D12 render-surface cross-include has been cut; broader
+  host include-surface cleanup remains.
 - App-side tests exist but are not consistently wired into CMake; some are
   stale and reference removed headers.
 
@@ -63,6 +64,9 @@ Completed boundary cuts:
   utility-window runtime contracts accept this service view instead of
   `EditorContext`, so concrete feature panels no longer depend on
   `Composition/EditorContext.h`.
+- Win32 now hands render startup a neutral
+  `Rendering::Host::EditorWindowRenderRuntimeSurface` value, and D3D12 no
+  longer includes `Platform/Win32/**` editor surface headers to obtain `HWND`.
 
 The root issue is not the existence of a single executable target by itself.
 The root issue is that shared app contracts are stored inside concrete layer
@@ -377,6 +381,17 @@ app/Host/D3D12/
 Then replace concrete Win32/D3D12 cross-includes with a neutral surface or
 factory contract.
 
+Completed first cut:
+
+- The old `Win32EditorWindowRenderRuntimeSurface` concrete adapter was removed.
+- `EditorWindowRenderRuntimeSurface` is now a value contract in
+  `Rendering/Host/EditorWindowRenderRuntime.h`.
+- Win32 fills that neutral contract during native surface capture; D3D12 reads
+  the native handle from the contract instead of including a Win32 editor
+  windowing header.
+- Remaining work in this phase is to move/rename host interface directories
+  and continue narrowing CMake include surfaces.
+
 ## Phase 6: Documentation Update
 
 Update `editor/AGENTS.md` after each completed boundary cut.