Publish renderer feature snapshot for canvas gates

docs/modernization/roadmap.md

@@ -883,6 +883,10 @@ mapping from persisted layer and brush blend indices to that planner, including
 fallback behavior for unknown nonzero indices. Both `Canvas::draw_merge` and
 `NodeCanvas` panorama rendering consume that shared gate, so the live app no
 longer has duplicate local blend-trigger logic.
+The OpenGL shader initialization path now stores a renderer-neutral
+`RenderDeviceFeatures` snapshot converted by `pp_renderer_gl`, and those live
+canvas gates consume that snapshot instead of rebuilding feature flags from
+individual `ShaderManager` extension booleans.
 The existing renderer classes are not yet fully
 behind the renderer interfaces.
 
@@ -1610,6 +1614,10 @@ Results:
 - `NodeCanvas` panorama rendering now consumes the same tested
   `pp_paint_renderer` canvas blend-gate planner as `Canvas::draw_merge`, so
   layer and primary-brush blend-trigger compatibility is centralized.
+- Shader initialization now publishes the OpenGL backend's renderer-neutral
+  feature snapshot through the legacy shader manager, and live canvas blend
+  gates consume that `RenderDeviceFeatures` value instead of hand-built
+  framebuffer-fetch/texture-copy flags.
 - Canvas equirectangular import drawing and depth export rendering now route
   depth/blend state and active texture units through the renderer GL backend
   mapping.