Route stroke mixer composite setup through helper

docs/modernization/debt.md

@@ -18,6 +18,12 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Recent Reductions
 
+- 2026-06-13: DEBT-0036 was narrowed again. `Canvas::stroke_draw_mix` now
+  reuses `legacy_canvas_stroke_composite_services.h` for mixer-pass retained
+  `kShader::CompDraw` binding and blend uniform writes, with the helper now
+  preserving caller-specific texture slot uniforms. Mixer framebuffer,
+  viewport/scissor/capability state, sampler binding, texture binding, and draw
+  execution remain retained Canvas code.
 - 2026-06-13: DEBT-0036 was narrowed again. `Canvas::draw_merge` checkerboard
   background shader setup and final merged-texture redraw setup now route
   through `legacy_canvas_draw_merge_services.h`. The retained Canvas path still

docs/modernization/roadmap.md

@@ -2992,6 +2992,10 @@ Results:
   checkerboard backgrounds and the final merged texture redraw over the grid;
   layer traversal, blend destination copies, sampler/texture binding, and draw
   ordering remain in the legacy Canvas path.
+- `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
+  binding, and draw execution remain retained.
 - Canvas thumbnail layer blending now uses the same canvas destination-feedback
   plan for framebuffer-fetch versus texture-copy decisions; the thumbnail draw
   itself still executes through retained OpenGL canvas code under DEBT-0036.