Focalworks is an addon for hexcasting adding a few (more to come!) iota-holder-related features:
Focus rigging, which allows you to trigger a hex upon reads or writes, and allows you to modify the iota passed in. Optionally, writes can also leave a boolean on the top of the stack to indicate whether it should go through.
Spellbook manipulation, allowing you to read and set the currently selected page.
Report issues to the Focalworks github. If you're not sure whether it's a bug or not, report it anyway.