Move canvas depth renderbuffers into GL backend

docs/modernization/roadmap.md

@@ -999,7 +999,9 @@ to OpenGL token mapping, plus the default
 render-target texture parameters, texture/renderbuffer targets, depth format,
 framebuffer targets, binding queries, attachment points, and completion status
 used by `RTT::create` and framebuffer bind/restore paths, also live in
-`pp_renderer_gl`. RTT clear color/depth masks, renderer API render-pass
+`pp_renderer_gl`. Depth renderbuffer allocation/storage/delete and framebuffer
+depth attach/detach sequences used by canvas object-drawing helpers now execute
+through tested `pp_renderer_gl` dispatch contracts. RTT clear color/depth masks, renderer API render-pass
 color/depth/stencil clear-mask and clear-value mapping, and color-write-mask query tokens also
 live in `pp_renderer_gl`. `RTT` no longer spells GL enum names directly.
 Renderer API primitive-topology to OpenGL draw-mode mapping, mesh index-type
@@ -2021,9 +2023,9 @@ Results:
   mapping.
 - Canvas thumbnail generation and object-drawing helpers now route saved
   viewport/clear/blend state, active texture units, readback format/type,
-  framebuffer copy targets, and renderbuffer/depth attachment parameters through
-  the renderer GL backend mapping; `src/canvas.cpp` no longer contains raw
-  `GL_*` constants.
+  framebuffer copy targets, and depth renderbuffer allocation plus framebuffer
+  depth attach/detach through tested renderer GL backend dispatch contracts;
+  `src/canvas.cpp` no longer contains raw `GL_*` constants.
 - Windows desktop OpenGL context creation now consumes a tested
   `windows_wgl_core_context_3_3_config()` catalog from `pp_renderer_gl`, moving
   the active WGL context/pixel-format attribute literals out of the platform