Plan thumbnail blend feedback copies

docs/modernization/roadmap.md

@@ -891,9 +891,10 @@ individual `ShaderManager` extension booleans.
 `pp_paint_renderer::plan_canvas_stroke_feedback` now models the current stroke
 shader's required destination feedback without changing the legacy shader math.
 Live `Canvas::stroke_draw` consumes that plan for main-brush, dual-brush, and
-stroke-pad destination-copy versus framebuffer-fetch decisions; thumbnail layer
-blending is the remaining direct canvas feedback branch before a fuller live
-paint-renderer execution boundary can take over.
+stroke-pad destination-copy versus framebuffer-fetch decisions. Thumbnail layer
+blending now consumes the same canvas destination-feedback decision for its
+legacy `TextureBlend` path; the full thumbnail compositing execution remains
+legacy OpenGL until a fuller live paint-renderer boundary can take over.
 The existing renderer classes are not yet fully
 behind the renderer interfaces.
 
@@ -1633,6 +1634,9 @@ Results:
   `pp_paint_renderer` stroke-feedback plan to decide whether framebuffer fetch
   supplies destination color or the legacy OpenGL path must copy the target
   texture before drawing.
+- Canvas thumbnail layer blending now uses the same canvas destination-feedback
+  plan for framebuffer-fetch versus texture-copy decisions; the thumbnail draw
+  itself still executes through retained OpenGL canvas code under DEBT-0036.
 - Canvas equirectangular import drawing and depth export rendering now route
   depth/blend state and active texture units through the renderer GL backend
   mapping.