Centralize legacy document image exports

docs/modernization/build-inventory.md

@@ -561,7 +561,9 @@ Known local toolchain state:
 - `pp_app_core_document_export_tests` covers export file targets, collection
   directory/stem targets, picked-directory stems, MP4 suggested names, and
   invalid export naming inputs, plus export-start license/canvas availability
-  decisions.
+  decisions, export menu executor dispatch, file/stem/collection export
+  execution dispatch, failed directory creation preservation, named depth/cube
+  export dispatch, and malformed export target rejection.
 - `pp_app_core_document_recording_tests` covers recording start/stop, clear,
   platform recorded-file cleanup, frame-count reset, export progress totals,
   and oversized progress-total clamping.
@@ -605,6 +607,12 @@ Known local toolchain state:
   overwrite prompts, document field updates, title updates, and keyboard/dialog
   cleanup. Retained legacy UI/canvas execution remains tracked by `DEBT-0040`,
   `DEBT-0041`, and `DEBT-0042`.
+- `src/legacy_document_export_services.*` is the current app-shell bridge
+  between `pp_app_core` document export execution plans and live equirectangular,
+  layers, animation-frame, depth, and cube-face export calls. It preserves
+  platform-specific export messages, directory creation, picker-selected stem
+  exports, Web prepared-file handoff, and legacy `Canvas` export execution while
+  retained renderer/document/platform ownership is tracked by `DEBT-0043`.
 - `src/legacy_history_services.*` is the current app-shell bridge between
   `pp_app_core` history plans and legacy `ActionManager`; toolbar and
   `NodeCanvas` hotkeys share it while document-history extraction remains