Trim recording loop and retain async worker state

docs/modernization/roadmap.md

@@ -133,7 +133,11 @@ Current architecture mismatches that must be treated as real blockers:
   ownership instead of raw global lifetime, and the Windows main-loop/VR
   coordination flags now use `std::atomic` instead of unsynchronized globals,
   while the main Win32 entrypoint now groups window/GL/task/VR state behind a
-  retained local state object instead of separate process-wide globals.
+  retained local state object instead of separate process-wide globals, the
+  prepared-file and canvas async workers now sit behind named retained local
+  worker-state helpers instead of bare static accessors, and `App::rec_loop()`
+  has a smaller local encode/update shell even though the retained recording
+  loop 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