When toggling "annotate" can go from showing valid output to an error

when editing the input it auto-updates if there's no error, so you can edit it to something invalid, it'll continue showing the last valid rendering, then when you toggle the checkbox it _needs_ to rerender and has to display the error

should probably store the last valid input as well, and use that when toggling the checkbox instead of the current input

repor:

* visit
* delete the last `f` from the input
* see still valid output
* toggle "annotate"
* see an error

Start with the linked CBOR web app and reproduce the behavior by editing the input, then toggling the "annotate" checkbox. Trace the input auto-update and checkbox rerender paths; done means toggling preserves the last valid rendering instead of showing an error caused by the current invalid input.

Written by the indexing model from the issue text.