Reject unsupported parsed PPI blend modes

docs/modernization/build-inventory.md

@@ -92,7 +92,7 @@ Known local toolchain state:
   `pp_paint_renderer`,
   `pp_ui_core`, `pano_cli`, and their current headless test binaries,
   including foundation binary-stream/event/logging/task queue coverage, PNG metadata and
-  decode, PPI header/layout/non-finite opacity rejection, settings document, document
+  decode, PPI header/layout/non-finite opacity and blend-mode rejection, settings document, document
   snapshot/per-layer-frame/move/duration/face-pixel/PPI export coverage,
   snapshot-embedded face-payload rejection, paint brush/final-blend/
   stroke-alpha-blend/stroke spacing/stroke stress/stroke-script coverage,

docs/modernization/roadmap.md

@@ -316,7 +316,8 @@ PNG IHDR metadata parsing, PPI header/project byte-layout/body-summary
 recognition, layer/frame indexing, dirty-face PNG payload metadata validation,
 asset-level RGBA PNG payload decoding, and a pure typed settings document
 model, with
-corrupt/truncated/unsupported, non-finite opacity, extreme-dimension, and key/value limit tests.
+corrupt/truncated/unsupported, non-finite opacity, unsupported blend-mode,
+extreme-dimension, and key/value limit tests.
 `pp_paint` has started with pure brush parameter validation/stamp evaluation,
 CPU reference math for the five current final RGBA shader blend modes plus the
 shader-style stroke-alpha blend modes used by pattern/dual-brush mixing, and deterministic