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

docs/modernization/roadmap.md

@@ -98,15 +98,17 @@ Current architecture mismatches that must be treated as real blockers:
   directly, and Linux FPS title reporting now uses an injected callback, but
   retained Apple bridging in `platform_legacy` and other platform/app coupling
   remain, even though iOS keyboard visibility and prepared-file save handoff
-  now also route through explicit Apple bridge callbacks.
+  now also route through explicit Apple bridge callbacks and Apple render-
+  context hooks plus iOS main-render-target binding now route through the same
+  bridge style.
 - `src/platform_legacy/legacy_platform_services.*` is still part of the live
   app shell.
 - `pp_panopainter_ui` still depends on `pp_legacy_app`.
 - `Canvas`, `NodeCanvas`, and `NodeStrokePreview` still own too much live
   OpenGL execution around the renderer boundary, even though `NodeCanvas`
   display resolve, cache-to-screen composite, post-draw mask/grid/current-mode
-  sequencing, and per-layer/per-plane retained draw execution now route
-  through retained draw-merge helpers.
+  sequencing, per-layer/per-plane retained draw execution, and shared
+  checkerboard background setup now route through retained draw-merge helpers.
 - `app_layout.cpp` and `app_dialogs.cpp` are still mixed shell/controller files
   rather than thin composition/binding surfaces.
 - `App`, `Canvas`, `Node`, retained workers, and platform entrypoints still use
@@ -115,7 +117,8 @@ Current architecture mismatches that must be treated as real blockers:
   ownership, even though most previously detached or raw app-facing worker
   launches now use owned `std::jthread` or service-owned worker queues and
   `AppRuntime` now owns render/UI workers with explicit `std::jthread`
-  shutdown semantics.
+  shutdown semantics while the Windows splash-dialog and HMD renderer workers
+  also use owned `std::jthread` lifecycle.
 - Modern C++23 usage exists in extracted components, especially `std::span`,
   explicit result/status objects, and a few concepts, but the live app still
   does not consistently express ownership, thread affinity, or renderer

docs/modernization/tasks.md

@@ -131,6 +131,8 @@ Current slice:
 - `NodeStrokePreview` final composite plus preview-texture copy now route
   through `legacy_node_stroke_preview_execution_services.h`, but the preview
   node still owns most live-pass and retained GL resource execution.
+- `NodeCanvas` merged-path and non-blend checkerboard background setup now also
+  route through `execute_legacy_canvas_draw_merge_background_setup(...)`.
 - `NodeCanvas` display resolve plus cache-to-screen checkerboard/cache-texture
   composite now route through `legacy_canvas_draw_merge_services.h`.
 - `NodeCanvas` smoothing-mask overlay, smoothing-mask face pass, grid keepalive
@@ -370,6 +372,9 @@ modernization foundation.
 Current slice:
 - app-owned render/UI runtime queues and cloud worker ownership are already
   moving behind owned runtime/service objects
+- Windows splash-dialog and HMD renderer worker ownership in `main.cpp` now
+  also use `std::jthread` with explicit stop requests instead of raw
+  `std::thread`
 - brush package import/export now use service-owned `std::jthread` workers and
   UI-thread completion handoff
 - prepared-file save work and grid lightmap launch now also use service-owned
@@ -585,6 +590,9 @@ Current slice:
 - iOS virtual-keyboard visibility and prepared-file save handoff now also route
   through explicit Apple bridge callbacks instead of direct `App::I` calls in
   `LegacyPlatformServices`
+- Apple render-context acquire/release/present hooks and iOS
+  `bind_main_render_target()` now also route through explicit Apple bridge
+  callbacks instead of direct `App::I` calls in `LegacyPlatformServices`
 - retained Apple callback injection and broader `platform_legacy` singleton
   reach are still open