Add document face compositor bridge

docs/modernization/build-inventory.md

@@ -247,6 +247,10 @@ powershell -ExecutionPolicy Bypass -File scripts\automation\apple-remote-build.p
 - `pp_document_ppi_export_tests` exports pure `pp_document` metadata,
   per-layer frame durations, and RGBA8 face payloads to PPI bytes through
   `pp_assets`, then decodes and reimports them for round-trip coverage.
+- `pp_paint_renderer_compositor_tests` now covers pure `pp_document` frame/face
+  compositing by expanding per-layer dirty face payload rectangles into a full
+  renderer-sized RGBA buffer with layer visibility, opacity, and blend mode
+  applied in document order.
 - `pano_cli simulate-document-export` exposes the same pure document-to-PPI
   export, asset-level decode, and document reimport path through JSON
   automation and is covered by `pano_cli_simulate_document_export_smoke`.