Extract app runtime tail, canvas camera shell, and preview sample services

docs/modernization/tasks.md

@@ -152,6 +152,9 @@ Current slice:
   `src/legacy_canvas_plane_data.cpp` instead of staying inline in
   `src/canvas.cpp`, which trims another retained data-ownership pocket from
   the live canvas shell.
+- The final camera/timelapse member definitions now also live in
+  `src/legacy_canvas_camera_services.cpp` instead of staying inline in
+  `src/canvas.cpp`, which trims another retained canvas shell pocket.
 - The `CanvasModePen` and `CanvasModeLine` interaction families now also live
   in `src/legacy_canvas_mode_pen_line.cpp` instead of staying inline in
   `src/canvas_modes.cpp`, which materially thins another retained pen/line
@@ -346,6 +349,12 @@ Current slice:
   `src/legacy_node_stroke_preview_runtime_services.*` instead of staying
   inline in `src/node_stroke_preview.cpp`, which trims another coherent
   preview runtime pocket while preserving the current live draw path.
+- The preview sample execution pocket for sample-point conversion, brush
+  vertex upload, request assembly, and the
+  `execute_legacy_canvas_stroke_sample(...)` call now also lives in
+  `src/legacy_node_stroke_preview_sample_services.*` instead of staying inline
+  in `src/node_stroke_preview.cpp`, which trims another coherent preview
+  execution pocket while preserving the live draw path.
 - `NodeCanvas::init()` plus the remaining `NodeCanvas::draw()` outer shell now
   also live in `src/legacy_node_canvas_draw_services.*` instead of staying
   inline in `src/node_canvas.cpp`, which materially reduces the live node to a
@@ -569,6 +578,11 @@ Current slice:
   instead of staying inline in `src/app.cpp`, which reduces the remaining app
   file to a thinner retained composition surface around startup and runtime
   delegation.
+- `App::clear()`, `App::check_license()`, `App::async_start()`,
+  `App::async_redraw()`, `App::async_end()`, and `App::async_swap()` now also
+  live in `src/legacy_app_runtime_shell_services.cpp` instead of staying
+  inline in `src/app.cpp`, which reduces the remaining app file to a thinner
+  retained shell around document routing and runtime thread entrypoints.
 
 Write scope:
 - `src/app.cpp`