Add OpenGL renderer capability target

docs/modernization/build-inventory.md

@@ -88,13 +88,14 @@ Known local toolchain state:
   treating `windows-clangcl-asan` as a passing sanitizer gate.
 - Android arm64 headless configure/build passes through root CMake and the
   `platform-build` automation wrapper for `pp_foundation`, `pp_assets`,
-  `pp_paint`, `pp_document`, `pp_renderer_api`, `pp_paint_renderer`,
+  `pp_paint`, `pp_document`, `pp_renderer_api`, `pp_renderer_gl`,
+  `pp_paint_renderer`,
   `pp_ui_core`, `pano_cli`, and their current headless test binaries,
   including foundation event/logging/task queue coverage, PNG metadata and
   decode, PPI header/layout, settings document, document
   snapshot/per-layer-frame/move/duration/face-pixel coverage, paint
-  brush/stroke/stroke-script coverage, renderer shader descriptor coverage,
-  UI color parsing, and layout XML parse coverage.
+  brush/stroke/stroke-script coverage, renderer shader descriptor and OpenGL
+  capability coverage, UI color parsing, and layout XML parse coverage.
 - `pano_cli inspect-image` reports PNG IHDR metadata as JSON and is covered by
   `pano_cli_inspect_png_metadata_smoke` with a tiny IHDR fixture.
 - `pano_cli inspect-project` reports validated PPI thumbnail/body byte layout,
@@ -122,6 +123,10 @@ Known local toolchain state:
 - `pp_renderer_api` owns the canonical PanoPainter shader catalog consumed by
   the legacy OpenGL app initialization path; `pp_renderer_api_tests` validates
   catalog size, key entries, duplicate rejection, and bad path rejection.
+- `pp_renderer_gl` owns headless OpenGL runtime capability detection consumed
+  by the legacy app initialization path; `pp_renderer_gl_capabilities_tests`
+  validates framebuffer fetch, map-buffer alignment, desktop GL float support,
+  GLES float/half-float extensions, and WebGL exclusion behavior.
 - `windows-msvc-vcpkg-headless` validates manifest install/configure/build/test
   for the current headless component matrix; see DEBT-0007 for remaining app
   and platform triplet migration.

docs/modernization/roadmap.md

@@ -384,8 +384,12 @@ Status: started. `pp_renderer_api` exists as a headless renderer-neutral target
 with texture descriptor, byte-size, viewport, mesh, readback bounds, command
 context, render device, shader program descriptor, mesh, render target,
 readback, trace interface validation, and the canonical PanoPainter shader
-catalog now consumed by the legacy OpenGL app initialization path. OpenGL
-classes are not yet behind these interfaces.
+catalog now consumed by the legacy OpenGL app initialization path.
+`pp_renderer_gl` now exists as the first OpenGL backend library and owns pure
+OpenGL capability detection for framebuffer fetch, map-buffer alignment, and
+float texture support. The legacy app delegates extension interpretation to
+that backend library, but the existing renderer classes are not yet fully
+behind the renderer interfaces.
 
 Implementation tasks:
 
@@ -404,6 +408,8 @@ Implementation tasks:
   - `Sampler`
   - `ShaderManager`
   - `Shape`
+- Keep OpenGL runtime capability decisions in `pp_renderer_gl` with headless
+  tests before moving GL object lifetimes behind backend types.
 - Preserve current shader behavior and asset paths.
 - Add deterministic GPU tests:
   - clear
@@ -619,6 +625,10 @@ Results:
   aggregate stroke-script counts/distances.
 - `panopainter_validate_shaders` passed, validating 25 shader programs and 7
   shader includes for stage markers and include graph integrity.
+- `pp_renderer_gl_capabilities_tests` passed on default MSVC, vcpkg-headless,
+  and Android arm64 configure/build, covering framebuffer fetch, map-buffer
+  alignment, desktop GL core float support, GLES float/half-float extensions,
+  and WebGL exclusion behavior.
 - PowerShell analyze automation returns JSON summaries and includes the shader
   validation target.
 - `windows-msvc-vcpkg-headless` configured through the Visual Studio bundled