Own runtime threads and thin platform/canvas seams

docs/modernization/debt.md

@@ -18,6 +18,24 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Reductions
 
+- 2026-06-16: `DEBT-0036` was narrowed again. `NodeCanvas` non-`draw_merged`
+  per-layer/per-plane retained draw execution now routes through
+  `execute_legacy_canvas_draw_merge_layer_plane(...)` in
+  `src/legacy_canvas_draw_merge_services.h` instead of keeping the erase,
+  temporary paint/composite, regular texture, and optional blend path fully
+  inline in `NodeCanvas::draw()`; retained layer traversal and broader canvas
+  renderer orchestration remain.
+- 2026-06-16: `DEBT-0003` was narrowed again. `AppRuntime` now owns its
+  render/UI worker threads as `std::jthread` with explicit stop requests in
+  `src/app_runtime.cpp` and `src/app_runtime.h` instead of raw `std::thread`
+  ownership; retained app task call sites, singleton composition, and broader
+  runtime/platform coupling remain.
+- 2026-06-16: `DEBT-0017`/`DEBT-0053` were narrowed again. iOS virtual-keyboard
+  visibility and prepared-file save handoff now route through explicit Apple
+  bridge callbacks in `src/platform_apple/apple_platform_services.*` consumed
+  by `src/platform_legacy/legacy_platform_services.cpp` instead of direct
+  `App::I` calls in those legacy platform methods; the retained Apple fallback
+  adapter and broader platform singleton reach remain.
 - 2026-06-16: `DEBT-0036` was narrowed again. `NodeCanvas` smoothing-mask
   overlay draw, smoothing-mask face pass, grid keepalive draw, heightmap draw,
   and current-mode draw now route through