Thin canvas draw seams and own grid worker

docs/modernization/tasks.md

@@ -132,8 +132,11 @@ Current slice:
   through `legacy_node_stroke_preview_execution_services.h`, but the preview
   node still owns most live-pass and retained GL resource execution.
 - `NodeCanvas` display resolve plus cache-to-screen checkerboard/cache-texture
-  composite now route through `legacy_canvas_draw_merge_services.h`, but
-  broader canvas draw orchestration is still inline.
+  composite now route through `legacy_canvas_draw_merge_services.h`.
+- `NodeCanvas` smoothing-mask overlay, smoothing-mask face pass, grid keepalive
+  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.
 
 Write scope:
 - `src/node_stroke_preview.cpp`
@@ -348,9 +351,9 @@ Mini-model packet:
 Status: In Progress
 
 Why now:
-Canvas imports/exports/saves, cloud transfer, brush import/export, grid
-lightmap work, stroke preview, and event persistence still launch detached
-threads. That is not a safe modernization foundation.
+The biggest app-facing async families have been moved off detached launches,
+but retained worker ownership and ad hoc runtime control are still not a safe
+modernization foundation.
 
 Current slice:
 - app-owned render/UI runtime queues and cloud worker ownership are already
@@ -361,8 +364,9 @@ Current slice:
   workers with explicit UI-thread handoff
 - canvas async import/export/save/open and timelapse export now also use owned
   worker queues instead of detached threads
-- preview background rendering and recording thread ownership now also use
-  `std::jthread`, but their retained loop/control flow is still open
+- preview background rendering, recording, and the retained
+  `NodePanelGrid::bake_uvs()` worker now also use `std::jthread`, but their
+  retained loop/control flow is still open
 
 Write scope:
 - `src/canvas.cpp`
@@ -563,6 +567,9 @@ Current slice:
   `App::set_platform_services()`
 - `platform_apple` clipboard, display/share, cursor, and save-ui-state calls
   now route through injected Apple bridge callbacks instead of `App::I`
+- `LegacyPlatformServices::prepare_storage_paths()` now routes Apple path
+  preparation through a narrow local helper instead of reading `App::I`
+  directly in that method body
 - retained Apple callback injection and broader `platform_legacy` singleton
   reach are still open