Extract OpenGL shader attribute bindings

docs/modernization/roadmap.md

@@ -393,8 +393,10 @@ format mapping for `Texture2D` image uploads and framebuffer status naming for
 `RTT` diagnostics. Mesh index-type and primitive-mode decisions used by legacy
 `Shape` drawing also live in `pp_renderer_gl`. The legacy app delegates
 extension, upload-format, framebuffer diagnostic, and mesh draw-mode
-interpretation to that backend library, but the existing renderer classes are
-not yet fully behind the renderer interfaces.
+interpretation to that backend library. The PanoPainter shader attribute
+binding catalog also lives in `pp_renderer_gl` and is consumed by legacy
+`Shader` creation. The existing renderer classes are not yet fully behind the
+renderer interfaces.
 
 Implementation tasks:
 
@@ -636,7 +638,10 @@ Results:
   WebGL exclusion behavior, upload types for RGBA8/RGBA16F/RGBA32F internal
   formats, image channel-count format mapping including invalid counts, and
   framebuffer status names, plus Shape index-type and fill/stroke primitive
-  mode mapping.
+  mode mapping. Shader attribute binding catalog validation covers the current
+  `pos`, `uvs`, `uvs2`, `col`, and `nor` bindings and rejects empty, unnamed,
+  null-name, and duplicate-name catalogs while preserving legacy shared
+  locations.
 - PowerShell analyze automation returns JSON summaries and includes the shader
   validation target.
 - `windows-msvc-vcpkg-headless` configured through the Visual Studio bundled