enum FrameTasks

Work deferred until the current frame is on screen.

Exists for the one thing a synchronous UI thread cannot otherwise express: a visible "before". A click handler about to spend seconds reading and parsing a large file can set its status text, hand the actual work to after, and return — the loop paints "Loading…", presents it, then runs the work. Doing both inline instead puts the state change and the stall in the same frame, so the status is never drawn and the window simply freezes with stale content, which is indistinguishable from nothing happening.

Not a thread pool and not a substitute for one: the work still runs on the main thread and still blocks it. What it buys is that the user is told what is blocking, and which file, before it starts.