Add renderer blit command contract

docs/modernization/roadmap.md

@@ -417,9 +417,10 @@ 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, trace
-interface validation, and the canonical PanoPainter shader catalog now consumed
-by the legacy OpenGL app initialization path.
+frame-capture byte-size helpers, frame-capture command validation,
+render-target blit validation, trace interface 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
@@ -720,8 +721,9 @@ Results:
 - `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, recording upload/readback/frame-capture command
-  capture, and invalid catalog rejection.
+  command-order validation, render-target blit validation, recording
+  upload/readback/frame-capture/blit command capture, and invalid catalog
+  rejection.
 - `pp_paint_renderer_compositor_tests` passed.
 - `pp_ui_core_color_tests` passed.
 - `pp_ui_core_layout_value_tests` passed.
@@ -815,13 +817,13 @@ Results:
   reintroduces raw `GL_*`/`WGL_*` constants outside the allowed legacy OpenGL
   implementation files.
 - `pp_renderer_api` now includes a headless `RecordingRenderDevice` with strict
-  command-order/texture-upload/readback/frame-capture validation; it records
-  commands, trace markers, texture uploads/readbacks, and frame captures, giving
-  automation a backend-neutral render path that does not require a window or GL
-  context.
+  command-order/texture-upload/readback/frame-capture/blit validation; it
+  records commands, trace markers, texture uploads/readbacks, frame captures,
+  and render-target blits, giving automation a backend-neutral render path that
+  does not require a window or GL context.
 - `pano_cli record-render` exercises that headless recording renderer and emits
   JSON command counts, target dimensions, backend name, trace/draw summary, and
-  texture-upload/readback/frame-capture command/byte totals for agent
+  texture-upload/readback/frame-capture/blit command/byte totals for agent
   automation, with an expected-failure smoke for oversized render/readback
   targets.
 - `pano_cli simulate-document-history` exercises pure document history