Extract app runtime shell, canvas render shell, and node tree services

docs/modernization/tasks.md

@@ -91,7 +91,7 @@ Status: In Progress
 
 Why now:
 `src/canvas.cpp` is still the biggest single architectural blocker at about
-1010 lines, with `src/canvas_modes.cpp` now materially thinner and the next
+429 lines, with `src/canvas_modes.cpp` now materially thinner and the next
 remaining render-shell pressure shifting toward preview/canvas nodes.
 
 Current slice:
@@ -142,6 +142,12 @@ Current slice:
   in `src/legacy_canvas_stroke_runtime_services.*` instead of staying inline in
   `src/canvas.cpp`, which trims another large retained live stroke/runtime
   pocket from the canvas shell.
+- `Canvas::draw_merge(...)`, the temporary-paint and merge-branch
+  orchestration helpers, final-plane composite, timelapse commit, create,
+  destroy, clear-context, and camera accessors now also live in
+  `src/legacy_canvas_render_shell_services.*` instead of staying inline in
+  `src/canvas.cpp`, which trims another large retained render/context shell
+  from the live canvas owner.
 - 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
@@ -521,7 +527,7 @@ Status: In Progress
 
 Why now:
 `src/app.cpp` still carries startup, frame flow, queue draining, recording,
-and composition logic in one 575-line file.
+and composition logic in one 292-line file.
 
 Current slice:
 - UI observer math now routes through `src/legacy_app_frame_services.cpp`
@@ -530,6 +536,14 @@ Current slice:
   retained helper.
 - Canvas toolbar refresh in `App::update()` now also routes through that helper
   file, materially shrinking `src/app.cpp`.
+- `App::draw(...)`, `App::update(...)`, `App::terminate(...)`,
+  `App::update_memory_usage(...)`, `App::update_rec_frames(...)`,
+  `App::res_from_index(...)`, `App::res_to_index(...)`,
+  `App::res_to_string(...)`, `App::rec_clear(...)`, `App::rec_start(...)`,
+  `App::rec_stop(...)`, `App::rec_export(...)`, `App::rec_loop(...)`, and
+  `App::render_thread_tick(...)` now also live in
+  `src/legacy_app_runtime_shell_services.cpp` instead of staying inline in
+  `src/app.cpp`, which materially thins the remaining frame/runtime shell.
 
 Write scope:
 - `src/app.cpp`
@@ -758,6 +772,12 @@ Current slice:
   `src/legacy_ui_node_attributes.*` instead of staying inline in `src/node.cpp`,
   which trims another coherent XML/Yoga attribute decoding pocket from the base
   scene-graph shell without changing its public surface.
+- `Node::destroy()`, `root()`, `set_manager(...)`, `added_to_root()`,
+  `handle_on_screen(...)`, template loading helpers, child add/remove/move
+  helpers, and child query helpers now also live in
+  `src/legacy_ui_node_tree_services.cpp` instead of staying inline in
+  `src/node.cpp`, which materially thins the remaining generic scene-graph
+  lifecycle/tree shell without changing the public surface.
 
 Write scope:
 - `src/node.cpp`