Own runtime threads and thin platform/canvas seams

docs/modernization/tasks.md

@@ -137,6 +137,10 @@ Current slice:
   draw, heightmap draw, and current-mode draw now also route through
   `execute_legacy_canvas_draw_merge_post_draw(...)`, but broader canvas draw
   orchestration is still inline.
+- `NodeCanvas` non-`draw_merged` per-layer/per-plane retained draw execution
+  now also routes through `execute_legacy_canvas_draw_merge_layer_plane(...)`,
+  but the node still owns substantial live layer traversal and renderer state
+  orchestration.
 
 Write scope:
 - `src/node_stroke_preview.cpp`
@@ -313,13 +317,21 @@ Mini-model packet:
 
 #### ARC-APP-004 - Move Render/UI Queues Into An Owned App Runtime Service
 
-Status: Ready
+Status: In Progress
 
 Why now:
 `App` still owns static render/UI queues, mutexes, condition variables, and
 thread ids. That makes thread safety hard to reason about and keeps platform
 entrypoints coupled to the singleton.
 
+Current slice:
+- render/UI queues, mutexes, condition variables, and thread identity already
+  live in `AppRuntime`
+- `AppRuntime` render/UI worker ownership now also uses `std::jthread` plus
+  explicit stop requests instead of raw `std::thread`
+- retained `App` composition, task call sites, and platform/runtime entrypoint
+  coupling are still not fully reduced behind the runtime contract
+
 Write scope:
 - `src/app.h`
 - `src/app.cpp`
@@ -570,6 +582,9 @@ Current slice:
 - `LegacyPlatformServices::prepare_storage_paths()` now routes Apple path
   preparation through a narrow local helper instead of reading `App::I`
   directly in that method body
+- 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`
 - retained Apple callback injection and broader `platform_legacy` singleton
   reach are still open