Own main workers and narrow Apple render hooks

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` merged-path and
+  non-blend checkerboard background setup now route through
+  `execute_legacy_canvas_draw_merge_background_setup(...)` in
+  `src/legacy_canvas_draw_merge_services.h` instead of keeping that shared
+  background loop inline in both branches of `NodeCanvas::draw()`; broader
+  canvas draw orchestration remains.
+- 2026-06-16: `DEBT-0003` was narrowed again. The Windows splash-dialog worker
+  and HMD renderer worker in `src/main.cpp` now use `std::jthread` with
+  explicit stop requests instead of raw `std::thread` ownership; retained
+  global VR state, Win32 message-loop ownership, and broader app runtime
+  coupling remain.
+- 2026-06-16: `DEBT-0017` was narrowed again. Apple render-context
+  acquire/release/present hooks and iOS main-render-target binding now route
+  through explicit 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` non-`draw_merged`
   per-layer/per-plane retained draw execution now routes through
   `execute_legacy_canvas_draw_merge_layer_plane(...)` in