Thin recording bridge and canvas draw seams

docs/modernization/debt.md

@@ -18,6 +18,18 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Reductions
 
+- 2026-06-16: `DEBT-0037` was narrowed again. `App::rec_loop()` in
+  `src/app.cpp` now delegates recording worker iteration orchestration into
+  `process_legacy_recording_worker_iteration(...)` in
+  `src/legacy_recording_services.cpp` instead of owning the wait/plan/encode
+  shell itself; retained recording loop control, readback call sites, and MP4
+  execution remain.
+- 2026-06-16: `DEBT-0036` was narrowed again. `NodeCanvas` checkerboard
+  background-plane callback setup now routes through
+  `make_legacy_canvas_draw_merge_background_checkerboard_plane(...)` in
+  `src/legacy_canvas_draw_merge_services.h` instead of keeping that callback
+  inline in `NodeCanvas::draw()`; broader canvas draw orchestration and
+  retained GL resource ownership remain.
 - 2026-06-16: `DEBT-0003` was narrowed again. Canvas async
   import/export/save/open background work now runs through an
   `AppRuntime`-owned queue/worker in `src/app_runtime.h/.cpp`, and

docs/modernization/roadmap.md

@@ -116,9 +116,10 @@ Current architecture mismatches that must be treated as real blockers:
   sequencing, per-layer/per-plane retained draw execution, and shared
   checkerboard background setup now route through retained draw-merge helpers,
   with the cache-to-screen checkerboard-plane callback setup also reduced and
-  the merged-path per-plane merged-texture draw plus the smoothing-mask face
-  shader/draw pass plus heightmap, current-mode, and grid-mode callback setup
-  now routed through the same retained helper family.
+  the merged-path checkerboard background-plane callback plus per-plane
+  merged-texture draw plus the smoothing-mask face shader/draw pass plus
+  heightmap, current-mode, and grid-mode callback setup now routed through the
+  same retained helper family.
 - `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
@@ -138,8 +139,9 @@ Current architecture mismatches that must be treated as real blockers:
   helper instead of a bare static accessor, the prepared-file worker and the
   canvas async import/export/save/open worker now live under `AppRuntime`
   instead of retained static app-events/canvas workers, and `App::rec_loop()`
-  now has a smaller local wait/iteration/encode shell even though the retained
-  recording loop still owns the worker-side readback flow.
+  now delegates worker-iteration orchestration into the retained recording
+  bridge even though that retained recording path still owns the worker-side
+  readback flow.
 - 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

@@ -151,6 +151,10 @@ Current slice:
   callback setup now also routes through
   `make_legacy_canvas_draw_merge_grid_modes_draw(...)`, but broader post-draw
   orchestration is still inline.
+- `NodeCanvas` checkerboard background plane callback setup now also routes
+  through `make_legacy_canvas_draw_merge_background_checkerboard_plane(...)`,
+  but the node still owns broader live layer traversal and renderer-state
+  sequencing.
 - `NodeCanvas` smoothing-mask face shader setup plus per-face draw execution
   now also route through
   `execute_legacy_canvas_draw_merge_smask_faces(...)`, but the node still owns
@@ -420,12 +424,10 @@ Current slice:
 - 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
-- `App::rec_loop()` now routes its frame encode/update chunk through a local
-  helper, its iteration-context setup now also routes through a local helper,
-  and its wait/plan/encode iteration shell now also routes through a local
-  helper, while `App::update()` no longer carries the dead update mutex
-  residue; retained recording loop control and readback ownership are still
-  open
+- `App::rec_loop()` now delegates its worker-iteration orchestration into the
+  retained recording bridge in `src/legacy_recording_services.cpp`, while
+  `App::update()` no longer carries the dead update mutex residue; retained
+  recording loop control, readback ownership, and MP4 execution are still open
 
 Write scope:
 - `src/canvas.cpp`