Route canvas clear state through GL backend

docs/modernization/build-inventory.md

@@ -395,10 +395,13 @@ Known local toolchain state:
   panorama rendering use the same tested active-texture dispatch for
   texture-unit switches, and their live viewport, scissor, and generic
   depth/blend/scissor capability changes now route through the same backend
-  dispatch contracts. `NodeCanvas` saved viewport/clear-color query,
-  density/offscreen color clear, and clear-color restore paths also use tested
-  `pp_renderer_gl` dispatch helpers. Retained desktop HMD eye rendering also
-  routes viewport execution through tested backend dispatch.
+  dispatch contracts. Retained `Canvas` stroke draw/commit, thumbnail
+  generation, object rendering, and `LayerFrame::clear` saved viewport or
+  clear-color query plus clear-color restore paths also use tested
+  `pp_renderer_gl` dispatch helpers. `NodeCanvas` saved viewport/clear-color
+  query, density/offscreen color clear, and clear-color restore paths use the
+  same helpers. Retained desktop HMD eye rendering also routes viewport
+  execution through tested backend dispatch.
   Legacy `Texture2D`, `TextureManager`, `Sampler`, and `RTT` public headers no
   longer expose raw OpenGL enum defaults; default texture formats, sampler
   filters/wraps, and render-target formats resolve through backend-owned
@@ -658,7 +661,8 @@ Known local toolchain state:
   tested viewport/scissor/capability dispatch consumed by retained Canvas,
   NodeCanvas, NodeStrokePreview, and HMD render-state paths,
   tested viewport query, clear-color query, and clear-color restore dispatch
-  consumed by retained `NodeCanvas` and `NodeStrokePreview` draw-state paths,
+  consumed by retained `Canvas`, `CanvasLayer`, `NodeCanvas`, and
+  `NodeStrokePreview` draw-state paths,
   tested color-write-mask dispatch consumed by retained `NodePanelGrid`
   transparent heightmap rendering,
   tested pixel-buffer allocation/readback/map/unmap/delete dispatch