Add renderer texture usage contract

docs/modernization/roadmap.md

@@ -414,14 +414,15 @@ Goal: make OpenGL an implementation detail and establish parity tests before
 adding new backends.
 
 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 byte-size helpers, texture-upload/readback command validation,
-frame-capture byte-size helpers, frame-capture command validation,
-render-target blit validation, texture-slot binding validation, blend-state
-validation, scissor-state validation, depth-state validation, trace interface
-validation, sampler-state validation, and the canonical PanoPainter shader
-catalog now consumed by the legacy OpenGL app initialization path.
+with explicit texture usage flags, texture descriptor, byte-size, viewport,
+mesh, readback bounds, command context, render device, shader program
+descriptor, mesh, render target, readback byte-size helpers,
+texture-upload/readback command validation, frame-capture byte-size helpers,
+frame-capture command validation, render-target blit validation, texture-slot
+binding validation, blend-state validation, scissor-state validation,
+depth-state validation, trace interface validation, sampler-state validation,
+and the canonical PanoPainter shader 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. It also owns the OpenGL texture upload-type mapping used
@@ -720,13 +721,14 @@ Results:
   per-layer frame duration, and PNG-encoded face-payload export to PPI bytes,
   plus malformed payload rejection at the export boundary.
 - `pp_renderer_api_tests` passed, including shader descriptor validation,
-  PanoPainter shader catalog validation, readback byte-size and command-order
-  validation, texture-upload byte-count validation, frame-capture byte-size and
-  command-order validation, render-target blit validation, texture-slot binding
-  validation, blend-state validation, scissor-state validation,
-  render-pass color/depth/stencil clear validation, shader-uniform write
-  validation, draw descriptor/range validation, backend-neutral resource
-  factory validation, texture-copy validation, recording
+  PanoPainter shader catalog validation, explicit texture usage validation,
+  readback byte-size and command-order validation, texture-upload byte-count
+  validation, frame-capture byte-size and command-order validation,
+  render-target blit validation, texture-slot binding validation, blend-state
+  validation, scissor-state validation, render-pass color/depth/stencil clear
+  validation, shader-uniform write validation, draw descriptor/range
+  validation, backend-neutral resource factory validation, texture-copy
+  validation, recording
   render-pass clear/scissor/depth/blend/shader-uniform/texture/sampler-bind/
   upload/texture-copy/readback/frame-capture/blit command capture, draw
   mesh-input capture, explicit draw-range capture, and invalid catalog
@@ -826,10 +828,11 @@ Results:
 - `pp_renderer_api` now includes a headless `RecordingRenderDevice` with strict
   renderer-owned resource factory and
   command-order/render-pass-clear/scissor-state/depth-state/blend-state/
-  texture-bind/sampler-bind/shader-uniform/texture-upload/readback/
-  frame-capture/blit validation plus explicit draw descriptor and texture-copy
-  validation; it creates validated textures, render targets, shaders, meshes,
-  and readback buffers, then records commands, trace markers, render-pass
+  texture-usage/texture-bind/sampler-bind/shader-uniform/texture-upload/
+  readback/frame-capture/blit validation plus explicit draw descriptor and
+  texture-copy validation; it creates validated textures, render targets,
+  shaders, meshes, and readback buffers, then records commands, trace markers,
+  render-pass
   color/depth/stencil clear intent, scissor state, depth state, blend state,
   shader uniform writes, texture/sampler binds, draw mesh inputs, explicit draw
   ranges, texture uploads/copies/readbacks, frame captures, and render-target