Harden stroke sampler edge tests

docs/modernization/build-inventory.md

@@ -95,7 +95,8 @@ Known local toolchain state:
   decode, PPI header/layout, 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/stroke-script coverage, renderer shader descriptor and OpenGL capability coverage, UI
+  stroke-alpha-blend/stroke spacing/stroke stress/stroke-script coverage,
+  renderer shader descriptor and OpenGL capability coverage, UI
   color parsing, and layout XML parse coverage.
 - `pano_cli inspect-image` reports PNG IHDR metadata as JSON and is covered by
   `pano_cli_inspect_png_metadata_smoke` with a tiny IHDR fixture.

docs/modernization/roadmap.md

@@ -320,7 +320,8 @@ corrupt/truncated/unsupported, 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
-stroke spacing/interpolation plus a pure text stroke-script parser.
+stroke spacing/interpolation plus duplicate-segment, non-finite, sample-limit,
+and 1001-sample stress coverage, plus a pure text stroke-script parser.
 `pp_document` has
 started with a pure canvas/layer/frame model, alpha-lock metadata, snapshot
 construction, per-layer frame metadata, layer metadata operations, frame