Narrow draw merge branch orchestration

docs/modernization/roadmap.md

@@ -3227,6 +3227,10 @@ Results:
   API mismatch while `Canvas::draw_merge_branch_orchestration()` still owns the
   remaining branch orchestration. `STR-016` remains blocked until the helper
   shape is simplified enough to move the per-layer composite block out cleanly.
+- `Canvas::draw_merge_branch_orchestration()` now drops the unused
+  `draw_checkerboard` parameter from the internal branch wrapper, shrinking the
+  remaining call-shape mismatch while the blocked draw-merge extraction still
+  stays in `STR-016`.
 - 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