Tighten STR-016 archival wording

docs/modernization/roadmap.md

@@ -3238,11 +3238,11 @@ Results:
 - `STR-016` completed on 2026-06-13 in `b9ed78e1`; the per-layer composite
   block moved out of `Canvas::draw_merge()`, and the follow-on
   `draw_checkerboard`/helper-shape cleanup is archived as `DEBT-0036`
-  reduction.
+  reduction only.
 - `Canvas::draw_merge_branch_orchestration()` and
   `Canvas::draw_merge_temporary_paint_branch()` later kept narrowing
-  `DEBT-0036`, but the draw-merge extraction itself is no longer blocked by
-  the helper API shape mismatch.
+  `DEBT-0036`, and this note remains archival context for the completed
+  draw-merge extraction.
 - Canvas main-brush, dual-brush, and stroke-pad draw paths now use the tested
   `pp_paint_renderer` stroke-feedback plan to decide whether framebuffer fetch
   supplies destination color or the legacy OpenGL path must copy the target