Narrow draw merge branch orchestration

docs/modernization/debt.md

@@ -401,6 +401,10 @@ agent or engineer to remove them without reconstructing context from chat.
   now drops the unused `draw_checkerboard` flag from the branch helper chain,
   shrinking the helper API mismatch while `Canvas::draw_merge_branch_orchestration()`
   still owns the remaining branch orchestration.
+- 2026-06-15: `DEBT-0036` was narrowed again. `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`.
 - 2026-06-14: `DEBT-0036` was narrowed again. `Canvas::draw_merge_branch_orchestration()`
   now routes the temporary erase, temporary paint, texture, and blend dispatch
   bodies through retained helpers inside `execute_canvas_draw_merge_branch_body(...)`;

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