Record draw merge paint branch reduction

docs/modernization/tasks.md

@@ -817,6 +817,10 @@ Progress Notes:
   should target the erase temporary composite branch or another similarly
   narrow final composite seam without reopening landed sample, mix, dirty, or
   framebuffer helpers.
+- 2026-06-13: `Canvas::draw_merge()` temporary paint branch execution now
+  routes through `make_legacy_canvas_draw_merge_temporary_paint_composite(...)`;
+  the live path still owns the concrete layer RTT, mixer RTT, sampler, and
+  plane callbacks.
 - 2026-06-13: `Canvas::stroke_draw_samples()` now routes face-indexed
   destination bind/copy/unbind and brush upload/draw through
   `execute_legacy_canvas_stroke_face_sample_polygon(...)`; the retained sample