add a comment about async code and TK

main.go

@@ -194,6 +194,16 @@ func moveSelectInFileList(target int) {
 	}
 }
 
+// TODO: by default, the event callback loop in TK is fully synchronous;
+// each event only arrives after the previous event has finished processing.
+// I'd like to make it so that multiple arrow presses cancel the in-flight
+// image update, but because the TK renderer is running with [LockOSThread],
+// just injecting goroutines willy-nilly results in horrible crashes.
+// Supporting async handling would require plumbing channels throughout
+// the render handler and making sure the main goroutine is the one that
+// exclusively touches the TK API.
+//
+// [LockOSThread]: https://go.dev/wiki/LockOSThread
 func keyPress(e *tk.Event) {
 	curr := directoryState.i
 	switch e.Keysym {