diff --git a/docs/modernization/debt.md b/docs/modernization/debt.md
index d679855..acf97f2 100644
--- a/docs/modernization/debt.md
+++ b/docs/modernization/debt.md
@@ -215,6 +215,10 @@ agent or engineer to remove them without reconstructing context from chat.
   branch orchestration now routes through `draw_merge_branch_orchestration(...)`;
   the retained path still owns the concrete per-branch framebuffer, sampler,
   and texture wiring.
+- 2026-06-13: DEBT-0036 was narrowed again. `Canvas::draw_merge()` final-plane
+  composite now routes through `draw_merge_final_plane_composite(...)`; the
+  retained path still owns the concrete merged-texture copy, checkerboard
+  redraw, and final blend/draw wiring.
 - 2026-06-13: DEBT-0036 was narrowed again. `NodeStrokePreview::draw_stroke_immediate()`
   now routes retained preview feedback/material/composite planning plus stroke
   shader uniform assembly through
diff --git a/docs/modernization/tasks.md b/docs/modernization/tasks.md
index fe784e7..70131c5 100644
--- a/docs/modernization/tasks.md
+++ b/docs/modernization/tasks.md
@@ -1887,6 +1887,42 @@ ctest --preset desktop-fast --build-config Debug -R "pp_paint_renderer_composito
 & 'C:\Program Files\Microsoft Visual Studio\18\Community\MSBuild\Current\Bin\MSBuild.exe' out\build\windows-msvc-default\tests\pp_paint_renderer_compositor_tests.vcxproj /p:Configuration=Debug /p:Platform=x64
 ```
 
+### STR-033 - Extract Draw Merge Final Plane Composite
+
+Status: Done
+Score: +1 renderer boundary and OpenGL parity
+Debt: `DEBT-0036`
+Scope: `src/canvas.cpp`, `src/legacy_canvas_draw_merge_services.*`, `tests/paint_renderer/compositor_tests.cpp`
+
+Goal:
+
+Move the final-plane composite call in `Canvas::draw_merge()` behind a
+retained helper so the merge path keeps only final-branch selection and
+concrete GL object wiring.
+
+Done Checks:
+
+- `Canvas::draw_merge()` no longer owns the final-plane composite call inline.
+- Regression coverage proves the final-plane helper preserves ordering and
+  checkerboard/blend behavior.
+- `docs/modernization/debt.md` records the reduced final-plane composite
+  surface.
+
+Closeout: `666c4dd3`
+
+Validation:
+
+```powershell
+ctest --preset desktop-fast --build-config Debug -R "pp_paint_renderer_compositor" --output-onfailure
+& 'C:\Program Files\Microsoft Visual Studio\18\Community\MSBuild\Current\Bin\MSBuild.exe' out\build\windows-msvc-default\tests\pp_paint_renderer_compositor_tests.vcxproj /p:Configuration=Debug /p:Platform=x64
+```
+
+### Completed Task Log
+
+| Date | Task | Score | Validation | Commit |
+| --- | --- | ---: | --- | --- |
+| 2026-06-13 | STR-033 | +1 renderer boundary and OpenGL parity | `ctest --preset desktop-fast --build-config Debug -R "pp_paint_renderer_compositor" --output-onfailure`; `& 'C:\Program Files\Microsoft Visual Studio\18\Community\MSBuild\Current\Bin\MSBuild.exe' out\build\windows-msvc-default\tests\pp_paint_renderer_compositor_tests.vcxproj /p:Configuration=Debug /p:Platform=x64` | `666c4dd3` |
+
 ### STR-012 - Extract Preview Final Composite Orchestration
 
 Status: Done