version 1/130803 by Dannii Willis
Some interpreters have limitations which mean that for very large story files the Undo function stops working. So far the only known example of this is Emily Short's Counterfeit Monkey, for which this extension was written. Ultra Undo will keep Undo working when the interpreter cannot, by using external files. You do not need to do anything other than include the extension - it will take care of everything for you, including cleaning up after itself (i.e., deleting those files when the player quits or restarts.)
There is a use option "maximum file based undo count" which controls how many how many turns can be undone using external files. By default that number is 20.
This extension is compatible with Conditional Undo by Jesse McGrew and Undo Output Control by Erik Temple.
The latest version of this extension can be found at <https://github.com/i7/extensions>. This extension is released under the Creative Commons Attribution licence. Bug reports, feature requests or questions should be made at <https://github.com/i7/extensions/issues>.