Route Canvas erase setup through helper

docs/modernization/debt.md

@@ -18,6 +18,11 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Recent Reductions
 
+- 2026-06-13: DEBT-0036 was narrowed again. `Canvas::stroke_commit` and
+  `Canvas::draw_merge` retained `CompErase` shader setup now route through
+  `legacy_canvas_stroke_erase_services.h`; Canvas still owns texture binding,
+  mask RTT binding, dirty/layer mutation, framebuffer feedback, and draw
+  execution.
 - 2026-06-13: DEBT-0036 was narrowed again. `NodeCanvas` live temporary-erase
   `CompErase` shader setup now routes through
   `legacy_canvas_stroke_erase_services.h`; the retained node path still owns

docs/modernization/roadmap.md

@@ -3009,6 +3009,10 @@ Results:
   shader setup helper for `CompErase` uniforms, while keeping per-onion-frame
   alpha updates, texture binding, temporary erase texture selection, and draw
   execution in the retained node path.
+- `Canvas::stroke_commit` and `Canvas::draw_merge` retained erase compositing
+  now share the stroke erase shader setup helper, while texture binding, mask
+  RTT binding, dirty/layer mutation, framebuffer feedback, and draw execution
+  remain in retained Canvas code.
 - `Canvas::stroke_draw_mix` now shares the retained stroke composite shader
   helper for mixer-pass `CompDraw` setup, while preserving its caller-specific
   texture slot uniforms. Mixer framebuffer/scissor state, sampler and texture