Route app async work through AppRuntime

docs/modernization/debt.md

@@ -18,6 +18,28 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Reductions
 
+- 2026-06-17: `DEBT-0039` was narrowed again. `App::dialog_browse()` in
+  `src/app_dialogs_workflow.cpp` now delegates retained browse-dialog button
+  wiring and selected-path open execution through
+  `src/legacy_document_open_services.*`, so the app dialog shell no longer
+  owns that document-open handoff inline while retained dialog creation,
+  unsaved-project prompting, project-open execution, and title/layer refresh
+  still remain.
+- 2026-06-17: `DEBT-0038` was narrowed again. The retained cloud upload and
+  download background execution in `src/legacy_cloud_services.cpp` now routes
+  through `AppRuntime::canvas_async_task` instead of a file-static worker
+  singleton, while retained prompt/progress lifetime, OpenGL context guards,
+  thumbnail loading, and transfer execution still remain in the cloud bridge.
+- 2026-06-17: `DEBT-0048` was narrowed again. The retained ABR/PPBR import path
+  in `src/legacy_brush_package_import_services.cpp` now uses
+  `AppRuntime::canvas_async_task` instead of a file-static worker singleton,
+  while the legacy preset panel remains the importer/storage owner and broader
+  brush asset/UI ownership transfer still remains open.
+- 2026-06-17: `DEBT-0044` was narrowed again. The retained asynchronous
+  timelapse export path in `src/legacy_document_export_services.cpp` now routes
+  through `AppRuntime::canvas_async_task` instead of a file-static worker
+  singleton, while retained `App::rec_export`, animation MP4 execution, and
+  mobile/Web completion paths still remain in the video-export bridge.
 - 2026-06-17: `DEBT-0036` was narrowed again. `src/canvas_layer.cpp` now
   routes retained `Layer` / `LayerFrame` render queueing through
   `src/renderer_gl/render_runtime_dispatch.h` instead of direct