Add renderer scissor state contract

docs/modernization/roadmap.md

@@ -419,8 +419,9 @@ 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, trace interface validation, and the canonical PanoPainter shader
-catalog now consumed by the legacy OpenGL app initialization path.
+validation, scissor-state 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
@@ -722,8 +723,9 @@ Results:
   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, recording blend/texture-bind/upload/
-  readback/frame-capture/blit command capture, and invalid catalog rejection.
+  validation, blend-state validation, scissor-state validation, recording
+  scissor/blend/texture-bind/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.
@@ -817,16 +819,16 @@ 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/blend-state/texture-bind/texture-upload/readback/frame-capture/
-  blit validation; it records commands, trace markers, blend state, texture
-  binds, uploads/readbacks, frame captures, and render-target blits, giving
-  automation a backend-neutral render path that does not require a window or GL
-  context.
+  command-order/scissor-state/blend-state/texture-bind/texture-upload/readback/
+  frame-capture/blit validation; it records commands, trace markers, scissor
+  state, blend state, texture binds, 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
-  blend-state plus texture-bind/upload/readback/frame-capture/blit command/byte
-  totals for agent automation, with an expected-failure smoke for oversized
-  render/readback targets.
+  scissor/blend-state plus texture-bind/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
   apply/undo/redo behavior and emits JSON layer/frame/history state for agent
   automation.