Security improvements to locking down play button and make sure one process only runs at once.

ptlinux/locking.py

@@ -24,7 +24,7 @@ def launcher_operation_lock(lock_path: Path, operation: str) -> Iterator[None]:
 			handle.seek(0)
 			owner = handle.read().strip() or "unknown operation"
 			raise OperationBusyError(
-				f"launcher files are busy ({owner}); close the updater and try again"
+				f"launcher files are busy ({owner}); wait for it to finish and try again"
 			) from exc
 		handle.seek(0)
 		handle.truncate()